obituary

nature structural biology • volume 8 number 6 • june 2001 489

G.N. Ramachandran, an outstanding fig-ure in the field of protein structure, passedaway at the age of 78, on April 7, 2001, inChennai (the erstwhile city of Madras),India. Ramachandran (G.N.R. or Ram tohis friends and associates) was the founderof the ‘Madras school’ of conformationalanalysis of biopolymers. His discovery ofthe triple helical structure of collagen in1955 and his analysis of the allowed con-formations of proteins through the use ofthe ‘Ramachandran plot’ rank among themost outstanding contributions in struc-tural biology, along with Pauling’sdescription of the α-helix and Watson andCrick’s discovery of the double helicalstructure of DNA.

G.N. Ramachandran (‘G’ stands forGopalasamudram, his native town, and‘N’ stands for Narayana Iyer, the name ofhis father) was born on October 8, 1922,in a small town not far from Cochin onthe southwestern coast of India. His fatherwas a Professor of Mathematics at a localcollege and thus had considerable influ-ence in shaping Ram’s interest in mathe-matics. After completing his school years,Ramachandran graduated in 1942 as thetop-ranking student in the B.Sc. (Honors)Physics course of the University ofMadras.

In 1942, Ramachandran joined theMaster’s program in ElectricalEngineering at the Indian Institute ofScience at Bangalore but was soonbrought into the Physics stream by thehead of the Physics Department, Sir C.V.Raman, who was awarded the 1930 NobelPrize in Physics for his discovery of theRaman effect. (Until Raman discoveredthis effect, it was generally believed thatscattered light can have its frequency shift-ed only towards the red end of the spec-trum, towards lesser energy. Ramandiscovered shifts in the frequency of scat-tered light towards the blue end of thespectrum, towards greater energy, violat-ing common sense and conventional wis-dom. Raman’s discovery was one of theimportant tools that dethroned the deter-ministic world of classical physics andlaunched the probabilistic world of quan-tum physics.) Under the guidance ofRaman, Ramachandran continued inPhysics, did his post-graduate research inthe areas of optics and X-ray topography

Ramachandran became a professor ofphysics at the University of Madras at theage of 29. The generous assistance andhospitable administrative support provid-ed by Sir A.L. Mudaliar enabledRamachandran to set up a fully equippedmodern X-ray crystallographic laboratoryat Madras.

In the beginning, Ramachandran hadtrouble deciding which projects were wor-thy of attention. Pauling’s lectures atCambridge on the structure of polypep-tide chains were still fresh in his mind, aswere Pauling’s publications on models ofthe α-helix and β-sheet structures. Heknew that he wanted to work on biologicalproblems, but the directions that he final-ly took were influenced by Professor J.D.Bernal who paid a visit to Madras duringlate 1952 and early 1953. Ramachandranasked Bernal for advice regarding suitableprojects, and Bernal suggested thatRamachandran could work on the struc-ture of collagen for which no satisfactorymodels had been proposed.

Ramachandran therefore directed hisattention to solving the structure of colla-gen. Using collagen samples from kanga-roo tail tendon, and assisted by GopinathKartha who was his first post-doc,Ramachandran produced X-ray diffrac-tion patterns from the collagen fibers.Using these data, and armed with relevantphysicochemical data, they started build-ing ball-and-stick models of the collagenstructure. Those efforts culminated in apaper1 published in Nature in 1954 on thestructure of collagen. Their proposedmodel for the collagen structure consistedof three parallel left-handed helicalpolypeptide chains standing side-by-sideand packed together in a hexagonal array.Each helix had 32 symmetry, hence 3residues per turn of the helix. Every thirdresidue in each chain was a glycine, and allthe glycines were located inside, facing thecommon central axis.

Subsequently, Ramachandran andKartha revised the model in light of moredetailed studies of the fiber diffractionpatterns. In the revised model, the num-ber of residues per turn became 3.3, sothat each of the 3 parallel left-handed heli-cal chains was made to coil around thecommon central axis in a right-handedway, giving rise to the now famous coiled

G.N. RamachandranEaswara Subramanian

of diamonds, and obtained a D.Sc. degreein 1947. This degree is equivalent to aPh.D., the difference being that the awardof a Ph.D. requires submitting a thesis on aresearch project under a supervisor whoalso suggested the project for the thesis,whereas a thesis for the D.Sc. degree

involves mainly the submission of a col-lection of papers describing the indepen-dent and original research work of acandidate.

In 1947, Ramachandran went to theCavendish Laboratory in Cambridge,England, then headed by Sir LawrenceBragg. At Cambridge, he worked withW.A. Wooster and A. Lang on a crystallo-graphic project and developed a mathe-matical theory for determining the elasticconstants of crystals from measurementsof diffuse X-ray reflections. He received aPh.D. from Cambridge University in 1949.While at Cambridge, Ramachandran metLinus Pauling and was deeply influencedby his lectures on modeling studies ofpolypeptide chains (see Fig. 1 for a pictureof them with colleagues during the 1960s).

Ramachandran returned to Bangalorein 1949 and worked as an AssistantProfessor in Physics until 1952. At thattime, Sir A.L. Mudaliar, the vice chancel-lor of the University of Madras and aneducator with a vision, was looking for asuitable person to start an experimentalphysics division at Madras and invited SirC.V. Raman to take this position. Ramandeclined the invitation and recommendedRamachandran instead. Thus, in 1952,

1922–2001

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obituary

coil structure. A paper2 presenting thisrevised model was published in Nature in1955. A picture of Ramachandran pre-senting a model for collagen during a lec-ture is shown in Fig. 2.

The proposed structure for collagencontained two interchain hydrogen bonds.Citing steric constraints, one of thesehydrogen bonds was considered unaccept-able by Alexander Rich and Francis Crick,who proposed an alternate model possess-ing a single interchain hydrogen bond3.Ramachandran felt that the frequentoccurrence of hydroxyproline in the colla-gen sequence (-Gly-Pro-Hypro-) impliedthe need for an extra hydrogen bond, pre-sumably through a water bridge betweenadjacent chains. This controversy, as towhether collagen structure had onehydrogen bond or two hydrogen bonds,raged for quite some time, but has nowbeen resolved. Studies by Helen Bermanand colleagues4 on single crystal struc-tures of oligopeptides incorporating colla-gen sequences appear to indicate thatthere are on average 1.5 hydrogen bonds.The controversy left an unfair legacy (oneoften found in biochemistry text books),which is the tendency to discuss the triple-helical structure of collagen without giv-ing due credit to Ramachandran. In arecent email to this author, paying tributeto Ramachandran, PaulineHarrison (Sheffield, UK)wrote: “... I think that hedid not get as much creditas he deserved for the col-lagen structure”. Onehopes that the future gen-erations will set the recordstraight.

Nevertheless, the contro-versy had a fortunate silverlining to it, and protein sci-ence was the beneficiary.The controversy hinged onthe minimum nonbondeddistance between atoms.Ramachandran thereforeset his associates to work ona survey of all crystal struc-tures, especially of aminoacids and peptides, for closecontacts involving C, N, Oand H atoms. The surveyrevealed that nonbonded atoms, in fact,approached each other much more closelythan the sum of their respective van derWaals radii would indicate was possible.Ramachandran and his associates thusarrived at a set of contact distances, calledthe ‘normal limits’, for each pair of atoms.Ramachandran also found that in order to

accommodate Pauling’s α-helix, the normallimits had to be further reduced by 0.1 Å, toyield the so-called ‘extreme limits’.

Ramchandran applied these limitingdistances to another problem — whethera polypeptide chain’s conformations maybe restricted because the chain’s backboneis essentially made of rigid planar peptideunits. Since two successive peptide unitsare hinged at the Cα atom, a pair of pep-tide units has only two degrees of freedom(rotations φ and ψ) around the bondslinking each Cα atom to the neighboringpeptide units. It was a brilliant flash ofinsight for Ramachandran to treat this asa mathematical problem of rotation oftwo rigid planes containing interactinghard spheres that must avoid bumpingagainst each other. Using the contact lim-its, if the rotations result in stericallyunacceptable contacts, such conforma-tions are considered disallowed. This rea-soning was the genesis of theRamachandran plot.

As the finer details of the map werebeing worked out, the first crystal struc-ture of a protein (that of myoglobin)became available, and a check of theobserved φ and ψ values for the proteinchain resoundingly confirmed the cor-rectness of the Ramachandran map. Thefirst international publication5 giving

details of the map appeared in 1963. Anexhaustive 155-page review articleappeared subsequently6.

R.E. Dickerson was among the first toepitomize the beauty and importance ofRamachandran plot in his 1969 mono-graph7 entitled The structure and action ofproteins, which was written with Irving

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Geis. Recently, in an email message to thisauthor, Janet Thornton wrote: “... I havenever met Professor Ramachandran, but hiscontribution ... rank(s) with Pauling’s dis-covery of the α-helix. It never fails to exciteme, when I see the Ramachandran plot andrealize how much of the beauty and order ofprotein structures is encapsulated by thisplot. I also think that this major discoveryhighlights the importance of clear thoughtand vision that do not always need expen-sive equipment and huge teams of people”.No one could have said it better.

In the late 1950s and 1960s,Ramachandran also worked on severalaspects of crystallography, such as phasedetermination in the presence of anom-alous dispersion, probability distributionof X-ray intensities, crystallographic sta-tistics, and so forth, and he devised thecorrect formula for calculating the X-rayphase angles using Bijvoet differences(which occur when anomalous scatteringof X-rays is present). He also wrote andedited several books and monographsdealing with crystallography and bio-polymer conformations. In addition, heorganized several international confer-ences on the conformation of biopoly-mers, which were often referred to as the‘Madras conferences’ and were attendedby many of the luminaries in structural

biology of the day, includingseveral Nobel laureates.

Ramachandran resignedfrom Madras in 1970 andspent a year as visiting pro-fessor at the BiophysicsDepartment of theUniversity of Chicago.During this visit, he deviseda new method involvingconvolution to reconstructthree-dimensional imagesfrom two-dimensional data,thus laying the foundationsfor computerized tomogra-phy.

On his return fromChicago, Ramachandranjoined the Indian Institute ofScience at Bangalore wherehe founded the MolecularBiophysics Unit (MBU) in1971. In 1977, he visited the

NIH in Bethesda, Maryland, USA as aFogarty scholar. In the same year, he waselected a Fellow of the Royal Society,London. He retired from MBU in 1978 butcontinued as a Professor of MathematicalPhilosophy at the Institute until 1989.

In the early 1980s, Ramachandranstarted showing symptoms of Parkinson’s

Fig. 1 Ramachandran (far right) with, from left to right, Dorothy Hodgkin, LinusPauling, and Sir A.L. Mudaliar. The photo was taken in 1967, during theInternational Symposium on Conformation of Biopolymers, organized byRamachandran at Madras.

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disease, and his health was deteriorating.He retired in 1989. The ailingRamachandran was cared for by his wifeRajam whom he married in 1945.However, in July 1998, Rajam died from aheart attack, and Ramachandran neverfully recovered from this blow. The onlyhigh point of this period occurred inAugust, 1999, when the InternationalUnion of Crystallography awarded the 5th

Ewald Prize to Ramachandran for his out-standing contributions to the field ofcrystallography. Specifically, the awardwas “in the area of anomalous scattering,… in the analysis of the structure offibers, collagen in particular, and, fore-most, for his fundamental works on themacromolecular conformation and thevalidation of macromolecular structuresby means of the Ramachandran plot”.

Since August 1999, he was under nurs-ing care in a hospital in Madras until hisdeath due to cardiac arrest in early April,2001. He is survived by two sons, Ramesh(Professor of Astrophysics at HarvardUniversity) and Hari (Institute of PlasmaPhysics, Ahmedabad, India), and a daugh-ter, Vijaya (Professor of ComputerScience, University of Texas at Austin).

Ramachandran was a man of many tal-ents. He was interested in classical Indianand Western Music, as well as in the philo-sophical systems of India and the West.During his brilliant and illustrious acade-mic career, the number of awards, medalsand citations conferred on him are toonumerous to be listed. As a man whobreathed science, and in terms of his last-ing contributions to structural biology,Ramachandran belonged to the sameintellectual class as Srinivasa Ramanujanin mathematics and Subrahmanya

nature structural biology • volume 8 number 6 • june 2001 491

Chandrasekhar in astrophysics. To knowmore about the life and times ofRamachandran, the reader is referred toRamachandran – a biography, by R. Sarma8.

Ramachandran’s death is a grievous lossnot only to his family members but also tothe Indian and international scientificcommunity and marks the passing away ofa brilliant mind with great passion forstructural biology. His scientific contribu-tions will remain as monuments to hissuperb intellect.

E. Subramanian is in the Department ofCrystallography and Biophysics, University

of Madras, H 21/8 Vaigai Street, Chennai -600 090, India. email:e_subramanian@hotmail.com or manian1@vsnl.com

1. Ramachandran, G.N. & Kartha, G. Nature 174,269–270 (1954).

2. Ramachandran, G.N. & Kartha, G. Nature 176,593–595 (1955).

3. Rich, A. & Crick, F. H. C. Nature 176, 915–916(1955)

4. Bella, J., Eaton, M., Brodsky, B. & Berman, H.M.Science 266, 75–81 (1994).

5. Ramachandran, G.N., Sasisekharan, V. &Ramakrishnan, C. J. Mol. Biol. 7, 95–99 (1963).

6. Ramachandran, G.N. & Sasisekharan, V. Adv. Prot.Chem. 23, 283–438 (1968).

7. Dickerson, R. E. & Geis, I. The structure andaction of proteins. (Benjamin/CummingsPublishing Company, Menlo Park, California;1969).

8. Sarma, R. Ramachandran – a biography. (AdeninePress, Schenectady, New York; 1998).

Fig. 2 Ramachandran delivering a seminar. The photo was taken in the 1960s, when this authorwas a student in Ramachandran’s lab. Ramachandran deliberately drew the α-helix as left-handedto drive home the message that each of the three individual helices in the adjacent figure repre-senting the triple-helix of collagen was left-handed. He encouraged the students to imagine a sin-gle left-handed α-helix, and then to imagine stretching it along the helical axis so that the numberof residues per turn became three, resulting in the conformation of an individual left-handed col-lagen helix.

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