7/28/2019 Ramchandran 1956

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7/28/2019 Ramchandran 1956

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1956 Nature Publishing Group

No. 4511 April 14, 1956 NATURE 711essential features of the earlier on e as regards th elocation of amino-acid residues and tho orientationof the NH- and CO-bonds. However, it is interestingto note that th e simpler non-coiled-coil structure hasbeen found to be th e basis of th e arrangement ofpolypeptide chains in polyproline5 and in polyglycine II Thus, it appears that th e triple chainstructure, with minor modifications, is a configurationwhich might bo fow1d also in other proteins andpolypeptides. There is, in fact, good evidence toshow that elastin belongs to this type 7Recently, tw o in teresting articles have appeared8'which discuss th e polypeptide chain configuration incollagen. Rich an d Cricks have criticized th e revisedstructure proposed from this laboratory, on considerations of stereochemistry and amino-acidsequence. Both these difficulties were known to usan d were in fact considered in a paper10 discussingthis structure in detail. It was found impossible toavoid short contacts if tw o good interchain hydrogenbondos were to be formed for every three residues.Consequently, models were built up which werestereochemically more satisfactory. It was thenfound, as Rich and Crick have found, that only onehydrogen bond can be formed for every three residuesin each chain of the triple chain. However, tw oconfigurations are possible, both of which ar e quitosatisfactory so fa r as the backbone of the structureis concerned. Th e tw o structures may be called th eplus and the minus structures, since they could beobtained from the one described oarlier4 by rotatingtho minor helices about their ow n axes through apositive or negative angle (