Loop structure in human serum albumin from Raman optical activity

Abstract

Vibrational Raman optical activity (ROA) measurements on human serum albumin are reported and discussed. At neutral pH, the ROA spectrum in the normal state N is dominated by bands assigned to α-helix together with a strong positive ROA band at ca. 1340 cm-1 assigned to a loop structure with local order possibly that of a 310-helix. On reducing the pH to 3.4, which generates the molten globule-like F state, only small decreases in the α-helix ROA bands occur, but the ca. 1340 cm-1 band decreases by ca. 40%, reflecting a loss of rigidity of part of the loop structure, possibly involving residues 292–315 since these connect the two halves of the molecule thought to be dissociated in the F state. These results suggest that the long loops comprising residues 106–119, 292–315 and 492–511 which connect subdomains A and B within each of the three domains I, II and III and previously described from x-ray studies simply as extended polypeptide might in fact have local order of a 310-helix. © 1998 John Wiley & Sons, Ltd.