How the Serpin α1-Proteinase Inhibitor Folds

Serpins are remarkable and unique proteins in being able to spontaneously fold into a metastable conformation without the aid of a chaperone or prodomain. This metastable conformation is essential for inhibition of proteinases, so that massive serpin conformational change, driven by the favorable energetics of relaxation of the metastable conformation to the more stable one, can kinetically trap the proteinase-serpin acylenzyme intermediate. Failure to direct folding to the metastable conformation would lead to inactive, latent serpin. How serpins fold into such a metastable state is unknown. Using the ability of component peptides from the serpin alpha 1PI to associate, we have now elucidated the pathway by which this serpin efficiently folds into its metastable state. In addition we have established the likely structure of the polymerogenic intermediate of the Z variant of alpha 1PI.