Distance constraints on macromolecular conformation.

Many physico-chemical studies are made on proteins to determine something of their solution conformation. For example the coat protein of Tobacco Mosaic Virus has been subjected to more non-crystallographic experimental studies to determine its native conformation than perhaps any other protein. Yet the sum of the experimentally determined constraints on its tertiary structure are surprisingly inadequate to fix its conformation. We are able to detect and remove minor inconsistencies in the data and then calculate a sampling of conformations consistent with all the data, which differ among themselves by r.m.s. deviations of the respective interresidue distances ranging from 5.7 angstrom to 15.8 angstrom. Some individual interresidue distances differ by as much as 50 angstrom from structure to structure. In order to restrict the range of possible conformations to something corresponding to the errors in a 10 angstrom resolution X-ray crystal structure, chemical and spectroscopic studies will have to be much more detailed than anything done to date. Our calculations appear to be useful in deciding which further experiments would be most productive.