NMR ANALYSIS OF MAIN-CHAIN CONFORMATIONAL PREFERENCES IN AN UNFOLDED FIBRONECTIN-BINDING PROTEIN

A 130-residue fragment of the Staphylococcus aureus fibronectin-bindin g protein has been found to exist in a highly unfolded conformation at neutral pH. Measurement of experimental NMR (3)J(HN2) coupling consta nts provides evidence for individual residues having distinct main-cha in conformational preferences that are dependent both on the amino aci d concerned and on neighbouring residues in the sequence. Analysis sho ws that these variations in the populations of individual residues can be explained in detail in terms of statistical distributions of confo rmational states derived from the protein data base. In particular, wh en the preceding residue has a beta-branched or aromatic side-chain, a significant increase occurs in the population of the less sterically restricted b region of phi, psi space. The results indicate that the l ocal structure of the fibronectin binding protein in solution, under c onditions where it displays full activity, approximates very closely t o a statistical random coil structure. This may be an important featur e in the biological role of this and other polypeptides involved in pr otein-protein interactions. (C) 1997 Academic Press Limited.