G. Kartha worked with G. N. Ramachandran on the structure of collagen. Their 1955 paper developed a model in which three polypeptide chains wind around one another, contributing to the explanation of the collagen triple helix. The proposed arrangement had to accommodate the amino acid composition, hydrogen bonding and the pattern of experimental X-ray diffraction.[ref]
Structure of collagen by G. N. Ramachandran and G. Kartha. Nature 176, 593–595, 1955; original paper reprinted in National Medical Journal of India, Classics in Indian Medicine
The history illustrates how a structural model is tested. A geometrically plausible arrangement can still require revision if its predicted repeat disagrees with measured X-ray diffraction. The value of the model lies in connecting molecular packing with several independent observations, while leaving its detailed geometry open to correction. A proposed protein structure and a later experimentally refined atomic structure represent different stages of that process.[ref]
Structure of collagen by G. N. Ramachandran and G. Kartha. Opening discussion of the revised 1955 model and disagreement of the earlier proposal with diffraction data
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