Role of the connectivity of secondary structure segments in the folding ofalpha(1)-antitrypsin

The native form of serpins (serine protease inhibitors) is metastable, whic h is critical to their biological functions. Spontaneous conversion from th e native form of serpins into a more stable conformation, called the "laten t" form, is restricted. To examine whether the connectivity of strand 1 of beta -sheet C to the hydrophobic core is critical to the serpin's preferent ial folding to the metastable native conformation, we designed a circularly -permuted mutant of alpha (1)-antitrypsin, the prototype serpin, in which s trand 1C is disconnected from the hydrophobic core. Conformation of the cir cular permutant was similar to that of the latent form, as revealed by equi librium unfolding, limited proteolysis, and spectroscopic properties. Our r esults support the notion that rapid folding of the hydrophobic core with c oncomitant incorporation of strand 1C into beta -sheet C traps the serpin m olecule into its native metastable conformation. (C) 2001 Academic Press.