Tag Archives: Structure

G. N. Ramachandran: A genius who laid the foundation of protein structures and 3D medical imaging

April 4, 2024ScienceIndian Scientist, Protein, Structure, X-ray crystallographyNeel

If you think you know it, then you do not know it, and if you know that you cannot know it, then you know it.

In one of his Mathematical Philosophy (MATPHIL) reports, G. N. Ramachandran elaborated on this interesting paradox from Kena Upanishad, describing the Divine force of the Universe, which conveys perpetual doubt and indefiniteness.

Prof. Gopalasamudram Narayana Ramachandran, affectionately known as GNR, was the finest molecular biologist whose seminal work in structural biology had put India on the world map of modern biology. The structural Biology era started with Linus Pauling and his colleague’s discovery of the -helical structures of polypeptides, which set the stage for our present-day understanding of protein function. The term molecular biology was coined in 1938 by Warren Weaver, a mathematician, and Director of the Natural Sciences Division at the Rockefeller Foundation, defining an amalgam of Physics, Chemistry, and Biology. Still, the molecular biology revolution started with the discovery of the double-helical structure of DNA by Rosalind Franklin, Francis Crick, James Watson, and Maurice Wilkins in the early 1950s. During that period, most of the work in molecular biology was done in UK and USA. Following this, a new structural fold comprising a coiled-coil triple helix was described by GNR in a series of papers published between 1954 and 1956 in Nature with his student Gopinath Kartha. Later in the 1950s and 1960s, he applied stereochemistry principles to generate a two-dimensional plot that accurately described allowed conformations of proteins. The map, now famously known as the Ramachandran plot, has become an inalienable part of molecular biology and biochemistry textbooks.

Passionate X-ray crystallographer

After graduating from St. Joseph’s College, Trichy, in 1939, Ramachandran joined the Electrical Engineering department at the Indian Institute of Science (IISc), Bangalore, and later moved to the Physics department. GNR studied crystallography all by himself while working for D.Sc. degree under the supervision of Sir. C. V. Raman. While transferring GNR to the Physics department from the Electrical Engineering department at the IISc, Raman, who was the Director of IISc at that time, said, â€œI am admitting Ramachandran into my department as he is a bit too bright to be in yoursâ€¦â€. After completing his doctorate, GNR moved to Cavendish Laboratory, Cambridge, where he worked on mathematical theory to determine elastic constants of cubic crystals from diffuse X-ray diffraction and obtained his second doctorate. After returning from Cambridge in 1949, he joined as an assistant professor at IISc, where he nurtured the X-ray diffraction laboratory. At the initiative of Dr. A. Lakshmanaswamy Mudaliar, the Vice Chancellor of Madras University at that time, GNR joined Madras University in 1952 as a founding member of the Physics department. Ramachandran started cutting-edge research in crystallography that included phase determination when anomalous dispersion is present, the probability distribution of X-ray intensities, crystallographic statistics, and so forth. He derived the correct formula to calculate the X-ray phase angles using Bijvoet differences, which occur during anomalous X-ray scattering. In 1971 he returned to IISc and established the Molecular Biophysics Unit (MBU), now a leading center of research in structural biology.

The Triple helix

It has been known for a long time that form and shape of all mammals are dependent on collagen protein which makes up a third of all proteins in their bodies. Collagen is vital for structural integrity; imperfection or instability in its structure causes many disease conditions. Ramachandran and Kartha used X-ray diffraction data on the collagen derived from the Kangaroo tail tendon to delineate its structure. The structural model had three parallel left-handed helical polypeptide chains, side-by-side coiled coils packed together in a hexagonal array. The triple helical structure of collagen has been described as â€œbraided in the manner of the pigtail of a long-haired maiden from Madras.â€ The collagen structure was alluding to the structural biologist of that time, and the work of GNR put India on the world map of structural biology. Ramachandran mentioned that he got the idea of a triple-helix coiled coil model from the rotation and revolution motion of the moon.

Despite his ground-breaking research, recognition did not come easily to GNR. Other leading structural biologists of that time, like Alexander Rich and Francis Crick, who were also working on collagen structure, did not accept the model citing steric issues and discrepancies in number of inter-chain hydrogen bonds. As collagen contains hydroxyproline residues GNR in his model had more than one hydrogen bond, which were mediated by water molecule. Now the controversy is well settled in favor of the â€˜Madras modelâ€™ of Ramachandran after the high-resolution crystal structure of collagen (PDB id 4OY5 [0.89 Ã…]) showed that there are, on average, 1.5 hydrogen bonds in the structure. Credit for collagen structure eluded him during his lifetime, but now the record has been set straight in favor of GNR. The basic three-dimensional structure of collagen unraveled by GNR helped us understand the molecular basis of its function and diseases caused by changes in its native structure.

The controversy on the collagen structure based on steric issues made GNR more determined, and he started working on formulating a general stereochemistry rule for protein structure that resulted in Ramachandran Plot, which has immensely benefitted protein science and drug discovery research.

Ramachandran plot

Proteins are made of twenty naturally occurring amino acids joined together like pearls in a necklace. It is called its primary structure, where amino acid residues are joined by rigid planer peptide bonds. This linear protein chain further folds into secondary (a-helix and b-strand), tertiary and quaternary structures acquiring a unique three-dimensional shape that dictates its function. Understanding a proteinâ€™s function or any dysfunction leading to disease conditions necessarily requires knowledge of its three-dimensional structure.

Ramachandran working with Ramakrishnan and Sasisekharan analyzed all the crystal structures of amino acids and observed that nonbonded atoms were closer to each other than the sum of their respective van der Waals radii. Using this and Paulingâ€™s a-helix information, GNR used mathematical calculation (without computersâ€¦!!!) to arrive at allowed rotations of rigid planer peptide planes that will lead to sterically acceptable contacts between them. The 2D plot of these pair of allowed angles, Phi-Psi (f –y), gave birth to the Ramachandran plot. The Ramachandran plot was proved correct later when the first crystal structure of a protein was determined. The plot remains valid today when around two lakh protein structures have been experimentally determined and their coordinates deposited in the Protein Data Bank (PDB). For accuracy and acceptability, all experimentally determined structures of proteins as well as predicted structures, must confer to this map. Like the Raman effect, Bose-Einstein statistics, and Chandrasekhar limit, the Ramachandran plot has immortalized the scientist behind it.

Describing Ramachandran plot Prof. Dame Janet Maureen Thornton, a senior scientist and director emeritus at the European Bioinformatics Institute(EBI), EMBL, had written, â€œIt never fails to excite me, when I see the Ramachandran plot and realize how much of the beauty and order of protein structures is encapsulated by this plot. I also think that this major discovery highlights the importance of clear thought and vision that do not always need expensive equipment and huge teams of peopleâ€.

Medical Imaging

G N Ramachandran (GNR) also made seminal contributions that made a deep impact to the field of three-dimensional medical imaging. In 1971 he published two exciting research papers on Projection Reconstruction; one titled â€˜Reconstruction of substance from shadow: 1. Mathematical theory with application to three-dimensional radiography and electron micrographyâ€™. In another publication co-authored with A. V. Lakshminarayanan published in the same year in Proceedings of National Academy of Sciences, USA, he suggested using convolutions in the spatial dimension. Both opened the window for creating three-dimensional (3D) images of human anatomy using two-dimensional (2D) images, which could provide depth information. This led to the development of the Computed Tomography scan (CT-scan), where several 2D X-ray images obtained at different angles and depths, called projections, are used to construct 3D images on a computer.

Magnetic Resonance Imaging (MRI) is another imaging technique that uses a projection reconstruction algorithm developed by Ramachandran. In the first publication describing MRI in Nature in 1973, Paul Lauterbur cited Ramachandranâ€™s algorithm as a method for projection reconstruction. Lauterbur, who received Nobel Prize in Physiology in 2003, had initially called the new imaging technique zeugmatography derived from the Greek word zeugma meaning â€œthat which is used for joining.â€ MRI uses linear gradient in a homogeneous magnetic field of a Nuclear Magnetic Resonance (NMR) spectrometer so that different points in the object experience a slightly different magnetic field. This leads to the NMR spectrum as a projection of the 2D object into a 1D spectrum. In MRI, several projections are acquired, and images are reconstructed using the projection reconstruction algorithm of Ramachandran.

Both CT-scan and MRI have benefited enormously from G N Ramachandranâ€™s 1971 papers, and he is rightly credited for having a deep impact on the â€˜Medical Imagingâ€™ field. In a nutshell, Ramachandranâ€™s contribution has revolutionized human radiology helping with a high-throughput, efficient, and accurate diagnosis, which has become a boon for the modern medical sciences.

Personal life and Vedanta

G N Ramachandran was born on October 8,1922 in Ernakulam in Kerala. He was the eldest son of G.R. Narayana lyer and Lakshmi Ammal. His father was a Professor of mathematics who taught him mathematics. After retiring from MBU, he continued as a Professor of Mathematical Philosophy at IISc until 1989. In 1999 GNR was awarded the 5th Ewald Prize by the International Union of Crystallography for his outstanding contributions in crystallography. He spent his final years in Chennai, where he passed away on April 7, 2001.

Syadvada and Saptabhangi of Jain philosophy had a profound impact on Ramachandran. In one of his papers published in the journal Current Science in 1982, he described their usage in Boolean Algebra. In addition to applying mathematics to biological problems, Ramachandran used mathematics to look into divinity. In â€˜Vedanta and Epistemologyâ€™ he wrote, â€œThere is a close analogy of these ideas of modern logical analysis with the concepts in Indian philosophy of the â€˜Infiniteâ€™ (Ananta), which is one of the attributes of Brahman (Absolute Reality). The Upanishads contain many statements to the effect that this Reality has contradictory properties … The logical similarity to the example of infinity in mathematics is very close. In the case of mathematical infinity, we have to say that although it is a number, it does not belong to the class of finite numbers, and therefore it can have contradictory properties such as being both greater than and smaller than itself.â€

Though his contributions like the Collagen triple-helix structure; Ramachandran plot; and Tomography should have got not one or two but three Nobel prizes, he remains a shining jewel missing in the Nobel crown.

Molecular mechanism of specificity in promoter DNA recognition

July 2, 2021Sciencec-myc, NMR spectroscopy, Promoter, Protein-DNA interaction, Structure, X-ray crystallographyNeel

Recognition of *c-myc* gene promoter by human RBMS1 protein. The figure shows RBMS1 protein scanning the DNA in search of its target sequence and binding to the sequenceâ€™s nucleotides in a specific manner. The surface view of the crystal structure of RBMS1 protein is shown bound with the bases of nucleotides of *c-myc* promoter. .

Decoding the codes of life stored in DNA is a challenge which is performed in a tightly regulated manner by the cell. Decoding involves reading the correct code at a right time by DNA binding proteins. The decoded information is then channeled through mRNA. This requires an efficient and highly specific interaction between protein and DNA that control some of the most important processes pertaining to cell survival and growth. Any dysregulation in the process can lead to malfunctioning of the cell and disease. Proteins search and bind specific sequence in the background of billions of bases in the genome. This happens through a combination of 1D sliding, 2D hopping, and 3D diffusion.

Understanding specificity of protein-DNA interactions is a long-standing question that has been attempted to understand many times by scientists all over the world. Thermodynamics and kinetics have always been discussed to be behind the matters concerning DNA binding specificity and affinity. The evidence, however, remains scarce when answering the crucial biological questions.

In this background we have worked on human RBMS1 protein that has been shown to directly regulate the c-myc gene expression levels in cancerous cells. In our study we have elucidate the molecular basis of RBMS1-promoter DNA interaction and understand the mechanism for specificity. The work provides the first structural and dynamics characterization of human RBMS1 protein, that controls the expression of c-myc proto-oncogene inside the human cell by its interaction with 7 base pair consensus sequence within the 21 bp promoter/ autonomous origin of replication region 2 kb upstream of c-myc proto-oncogene.

During the work we overcame different challenges. Bioinformatic studies have failed to correctly identify the domain boundary and this was leading to protein instability. It required a careful human analysis using some of fundamentals of molecular biophysics to redesign the construct. We extended the boundary by 5 residues which lead to expression of highly stable RBMS1 protein. This is a lesson for students who blindly trust bioinformatics results and artificial intelligence.

We performed extensive binding assay with different DNA sequences varying the bases and length of the sequences to answer the question of specificity. We determined the 2.57 Ã… crystal structure of RBMS1 in its promoter DNA bound state that provided atomic-resolution insight into specific binding of individual nucleotides of DNA with the protein. The NMR structure of free RBMS1 was solved, as the protein did not crystallize, most likely due to its inherent flexibility, which we confirmed through NMR relaxation dynamics. The protein undergoes a hinge-like motion in order to bind with the specific DNA which facilitated by flexibility in the linker region. The X-ray structure of RBMS1-c-myc promoter DNA complex and solution NMR structure of RBMS1 protein helped us to delineate the non-canonical binding mode of RBMS1 with the promoter DNA.

In a nutshell the mechanism of specificity of RBMS1 binding with promoter is driven by the thermodynamics and the dynamic domain re-organization, which is responsible for conferring specificity and affinity. The work has implications for understanding general mechanism of protein-DNA interactions that involves sliding, hopping and diffusion during stochastic target search process in a dense nucleus. In addition, the work is likely to aid in designing future anti-gene therapies.

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References

Aggarwal P* and Bhavesh NS* (2021) Hinge like domain motion facilitates human RBMS1 protein binding to proto-oncogene c-myc promoter. Nucleic Acids Res. 49, 5943-5955
Structure co-ordinates: Protein Data Bank (PDB) accession numbers 6M75 and 7C36.

Structural identification of a cryptic target for drug discovery against urinary tract infections

July 24, 2020Sciencedrug discovery, E. Coli, Molecular Dynamics simulations, Structure, UTI infection, X-ray crystallographyNeel

Atomic-resolution structure of YadV, a usher chaperone from Uropathogenic E. coli (PDB id 5GHU). Crystal structure was determined by Nishant Kumar Pandey *(Left)*. Ms. Garima Verma and Dr. Gajraj Singh Kushwaha performed MD simulations (Right)

1.63 Ã… crystal structure of a usher chaperone from Uropathogenic E. coli (PDB id 5GHU)

Urinary tract infections (UTIs) are the most common and recurrent bacterial infections worldwide and are a major cause of morbidity. More than 150 million people worldwide are affected by UTIs. Gram-negative bacteria called Uropathogenic Escherichia coli (UPEC) is the primary pathogen that cause UTI. Adhesion of bacterial cell to human cell is primary requisite for bacterial pathogenesis, which is mediated by number of fibrilar and non-fibrilar adhesin molecule produced by bacteria. Fibrilar adhesin are named as fimbriae or pili and plays important role in inter-bacterial adhesion which leads to bacterial aggregation subsequently further colonisation and biofilm formation. Biofilm formation helps bacteria to evade host immune response, better survival in stress conditions and provides resistance to anti-microbial molecules and antibiotics. This is considered main reason for recurrent infection and is attributed to fimbriae assisted adhesion. Therefore, it is necessary to block adhesion by identifying new targets and developing new drugs against those targets.

There are helper protein molecules called chaperone proteins, which are necessary for synthesis of these fimbriae or pili. However, the exact mechanism fimbriae or pili biogenesis is still not fully understood. In this study we have determined 1.63 Ã… crystal structure of one such helper protein called YadV chaperone protein, which helps in synthesis Yad pili. The monomeric structure looks like a boomerang shape with N-terminal arm having immunoglobulin (Ig) like fold and C-terminal arm has Î²-barrel fold. Interestingly for the first time proline lock in the closed conformation has been observed in the structure of Yadv determined by us. Although the closed lock state, which is a resting state of the molecule has been proposed for all types of UPEC pili chaperone still it was not observed previously. Using molecular dynamics simulations we explained the opening and closing of the flexible proline lock. The proline-proline lock plays an important role in the chaperone-mediated subunit assembly, which is found in an open conformation in chaperone-subunit complex while we observed the closed conformation in subunit free structure. The observation of the closed conformation, a cryptic state, likely to be important target for design and discovery of pilicide that could bind to proline lock and maintain the lock in a closed conformation. This will lead to abolishment of pilus biogenesis that will block adhesion of UPEC to human cell. We have already shortlisted few inhibitors targeting this site on YadV.

The work was supported by a grant from the Basic Research in Modern Biology task force of Department of Biotechnology, Government of India.

Trivia: The name of protein changed from EcpD to YadV during the course of studies. Further, the structure prediction tools have predicted it to be a eight-stranded Î²-barrel protein and most even predicting to be an Outer Membrane Protein (OMP) (see below figure for one of the wrong prediction).

Therefore, we cloned it without signal sequence and expressed tag-free expecting to over-express as inclusion bodies. But the protein over-expressed as soluble, in large amount and as monomer in solution. All these and final structure proved the structure prediction completely wrong.

References

Pandey NK, Verma G,Â Kushwaha GS, Suar M andÂ Bhavesh NSÂ (2020) Crystal structure of the usher chaperone YadV reveals a monomer with the proline lock in closed conformation suggestive of an intermediate state.Â FEBS Lett.. 594, 3057-3066.
Structure co-ordinates: Protein Data Bank (PDB) accession numbers 5GHU.

Structure of an intermediate state during protein unfolding

January 24, 2020ScienceNMR spectroscopy, Protein, Protein Folding, StructureNeel

Cover art (Designed by Anupam Patra) featured on 21st Jan 2020 issue of Biophysical Journal (Left). Dr. Harshesh Bhatt and Dr. Akshay Kumar Ganguly (Right)

Proteins are the unique molecules; they read the code of life in genes and their own codes are also hidden in genes. Therefore, they are called architect, pillars and workhorses of life. A vast majority of proteins requires a well-defined three-dimensional shape and flexibility for their specific and regulated function inside the cell. Hierarchy of protein structure starts with primary structure consisting of individual amino acid residues, which then organizes itself into helices or sheets to form secondary structures. The great Prof. G. N. Ramachandran was the first to codify geometry of the secondary structural elements in the form of backbone torsion angles. The iconic plot is called Ramachandran Plot. Proteins further fold these secondary structural elements into tertiary and quaternary structures.

Process of formation of these structures, called Protein Folding, starts immediately at their birth place called Ribosomes and most proteins emerge as perfectly folded native structure at the end of their complete synthesis. However, there are few which require helper protein molecules called chaperone to correctly shape them. Different kinds of protein have different lifespan and at the end of it they are degraded to individual units with the help of another set of protein molecules, the process called Protein Unfolding. Both folding and unfolding processes are very specific, rapid and follows a well-defined path. Levinthal Paradox described by Prof. Cyrus Levinthal concluded that had it been a random search process among all possible conformation it would take astronomical age to fold a protein. Any aberration in folding-unfolding processes leads to dysregulation and sometimes formation of aggregated state, resulting in disease conditions such as Alzheimer and Parkinson disease.

Prof. Christian B. Anfinsen had used ribonuclease A as a model showed that primary sequence of the protein under a particular environmental conditions (temperature, solvent concentration and composition, etc.) at which folding occurs, dictates formation of native structure, which is a unique, stable and kinetically accessible minimum of the free energy. Several studies have demonstrated that proteins unfold under different physical and chemical conditions in a test tube and refold back to their native confirmation upon removal of such conditions. This helped the experimentalists to follow folding-unfolding pathways at a high spatial and time resolution and understand mechanisms. Landscape funnel model of protein folding is currently widely accepted model that describes a protein’s journey through the crests and troughs of internal free energy and degrees of freedom to reach the folded state from rapidly exchanging ensemble. Proteins also take a trek through the funnel during their unfolding.

The key to understanding protein (un)folding mechanism, which is still a challenge, is high-resolution structural characterisation of all states along the funnel. In this regards solution-state NMR spectroscopy is unparalleled in providing atomic-resolution structural and dynamics information of all the states, folded, unfolded and intermediates including invisibles, along the funnel. In this work we have used a canonical RNA recognition motif (RRM) from ETR3 protein (involved in muscular dystrophy disease) to understand the unfolding mechanism of RRM containing protein. This is important as a similar motif in TDP-43 protein aggregated and eventually leads to neuromuscular disease conditions due to formation of non-native structural elements. We determined the atomic-resolution structure and dynamics of folded native state (at bottom of the funnel) and an unfolding intermediate at the middle of the funnel and performed structural and dynamics characterisation of the unfolded ensemble rapidly dancing the top of the funnel. Our data indicates that intermediate state has folded like structure but swollen and dynamics. It allows solvent to access its core more easily than the folded structure. The edges of secondary structural elements are the initiation sites of unfolding. Although the unfolded state is very dynamic and lacks any structural elements still it show bias for certain structural propensities which appears like keeping a memory of their folded state.

We believe that the atomic-resolution characterisation of unfolding pathway of a canonical RNA recognition motif is likely to help in understanding the unfolding events in other RRMs involved in disease causing conditions upon misfolding.

The study might also help in understanding those systems where protein is refolded from the purified inclusion bodies. In those cases there could be presence of minor population of folded-like but not fully folded native structure.

The work was primarily done by Dr. Harshesh Bhatt and Dr. Akshay Kumar Ganguly and FCS work was performed in collaboration with Dr. Sobhan Sen, School of Physical Sciences, Jawaharlal Nehru University (JNU), New Delhi. The cover art was designed by Mr. Anupam Patra, Ph.D. student.

References

Dill K.A. and Chan H.S. (1997) From Levinthal to pathways to funnels. Nat. Struct. Biol. 4: 10-19
Bhatt H, Ganguly AK, Sharma S, Kushwaha GS, Khan MF, Sen S and Bhavesh NS (2020) Structure of an unfolding intermediate of an RRM domain of ETR-3 reveals its native-like fold. Biophys. J. 118, 352-365.
Structure co-ordinates: Protein Data Bank (PDB) accession numbers 2MY7 and 2MY8. Sequence-specific resonance assignments: BioMagResBank (BMRB) IDs: 19316 and 19685.

First report of molecular mechanism of RNA recognition in Malaria parasite

December 12, 2018Scienceà¤ªà¥à¤°à¥‹à¤Ÿà¥€à¤¨, à¤ªà¥à¤²à¤¾à¤œà¥à¤®à¥‹à¤¡à¤¿à¤¯à¤®, à¤®à¤²à¥‡à¤°à¤¿à¤¯à¤¾, Malaria, NMR spectroscopy, Plasmodium, Protein, RNA, StructureNeel

Structure of the PfSR1-RNA complex. Dr. Akshay Kumar Ganguly and Ms. Garima Verma who did the work.

Among the vector borne diseases malaria affects the maximum population. In 2017 alone there were about 22 crore cases more than 4 lakh death worldwide with India accounting for 6% of them¹. Malaria is caused in humans when a female Anopheles mosquito transfer protozoan parasites of the genus Plasmodium and Plasmodium falciparum is the most lethal of the malarial parasites. The economic consequence of this widespread disease is also apparent from the fact that malaria endemic countries have much lower GDP growth than countries free from malaria². In recent years drug resistance in malaria has emerged as a major threat to the public health. It is thus, imperative to elucidate the ways in which this parasite thrives in its hosts as well as the various mechanisms it employs to sustain an infection, in order to be able to effectively combat this menace. Malaria parasite uses an intelligent mechanism called alternate splicing to generate protein diversity. Alternate Splicing is one of the evolved mechanisms in higher organisms to produce different protein from a single gene by differentially processing the transcribed mRNA. This gives the parasite an added advantage to evade the drugs. To understand this important cellular event in malaria parasite we delineated the molecular mechanism of RNA binding of one such protein called serine/arginine rich (SR) protein of P. falciparum (PfSR1)⁵, which is the first such study in apicomplexans. Using Nuclear Magnetic Resonance (NMR) spectroscopy we determined atomic-resolution solution structures of PfSR1 protein⁶ in free and RNA bound states.

Supported by thermodynamic quantification we found that RNA binding domains of PfSR1 protein have contrasting preference for RNA while first domain has preference for pyrimidine especially 5â€™cytosine, other prefers purines (A or G), possibly due to different charges of the surface of both domains.

Our work opens a new window to understand how malaria parasite is able to produce 20% more proteins from its 5700 genes^3-4 which makes it more complex than many of the organisms having more genes than it and easy to evolve into drug resistant one.

The work was primarily done by Dr. Akshay Kumar Ganguly and was actively supported by Ms. Garima Verma.

References

World Malaria Report 2018 (https://www.who.int/malaria/publications/world-malaria-report-2018/en/)
Gallup JL and Sachs JD. (2001).The economic burden of malaria. Am J Trop Med Hyg 64, 85-96
Gardner MJ, Hall N, Fung E, White O, Berriman M, Hyman RW, et al. (2002). Genome sequence of the human malaria parasite Plasmodium falciparum, Nature. 419 498-511.
Sorber K, Dimon MT and DeRisi JL. (2011) RNA-Seq analysis of splicing in Plasmodium falciparum uncovers new splice junctions, alternative splicing and splicing of antisense transcripts. Nucleic Acids Res 39, 3820-3835.
Eshar S, Allemand E, Sebag A, Glaser F, Muchardt C, Mandel-Gutfreund Y, et al. (2012). A novel Plasmodium falciparum SR protein is an alternative splicing factor required for the parasitesâ€™ proliferation in human erythrocytes, Nucleic Acids Res 40, 9903-9916.
Ganguly AK, Verma G and Bhavesh NS(2019) The N-terminal RNA recognition motif of PfSR1 confers semi-specificity for pyrimidines during RNA recognition.Â J. Mol. Biol. 431, 498-510
Structure co-ordinates: Protein Data Bank (PDB) accession numbers 2N3L and 2N7C. Sequence-specific resonance assignments BioMagResBank (BMRB) IDs: 25650, 25800, 25779.