LOOP STRUCTURE IN HUMAN SERUM-ALBUMIN FROM RAMAN OPTICAL-ACTIVITY

Vibrational Raman optical activity (ROA) measurements on human serum a lbumin are reported and discussed. At neutral pH, the ROA spectrum in the normal state N is dominated by bands assigned to alpha-helix toget her with a strong positive ROA band at ca. 1340 cm(-1) assigned to a l oop structure with local order possibly that of a 3(10)-helix. On redu cing the pH to 3.4, which generates the molten globule-like F state, o nly small decreases in the alpha-helix ROA bands occur, but the ca. 13 40 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 describ ed from x-ray studies simply as extended polypeptide might in fact hav e local order of a 3(10)-helix. (C) 1998 John Wiley & Sons, Ltd.