CORRELATIONS BETWEEN BIOLOGICAL-ACTIVITY AND STRUCTURAL-PROPERTIES FOR 2 SHORT HOMOLOGOUS SEQUENCES IN THYMOSIN BETA-4 AND GELSOLIN

Gelsolin and thymosin beta 4 appear to be two important actin-associat ed proteins involved in the regulation of actin polymerization. It has been widely demonstrated that thymosin is the major cellular actin-se questering factor shifting the polymerization equilibrium of actin tow ards a monomeric state. At the same time gelsolin, a Ca2+ and inositol phosphate sensitive protein, regulates actin filament length. The int eractions of these two proteins with actin are rather complex and requ ire the participation of several complementary peptide sequences. We h ave identified a common motif, (I, V)EKFD, in the two proteins in the functional sequences so far examined. Gelsolin- and thymosin beta 4-re lated peptides including the common motif were synthesized and their s tructural and functional properties studied. These two sequences exert a major inhibitory effect on salt-induced actin polymerization. We us ed circular dichroism and Fourier-transform infrared spectroscopy to s how that the two synthetic peptides present some secondary structure i n solution. As far as the peptide derived from the thymosin sequence w as concerned, alpha-helical structure was induced by trifluoroethanol as observed with the full-length molecule. These experiments underscor e the importance of the conformational state of peptide fragments in t heir biological activities. ELISA and fluorescence measurements have b een used to identify the binding regions of these fragments to a C-ter minal region (subdomain 1) of the actin sequence. Our results also emp hasize the relationship between the propensity of small sequences to f orm secondary structures and their propensity for biological activity as related to actin interaction and inhibition of actin polymerization . (C) Munksgaard 1996.