Computer modelling of human alpha 1-antitrypsin reactive site loop behaviour under mild conditions

Human ai-antitrypsin (cti-PI) is a member of the serpin superfamily of proteins. The reactive site loop (RSL) of the serpin binds to the active site of its target proteinase. Deficiency of ai-antitrypsin is associated with a spontaneous conformational transition in the molecule which leads to a polymer formation. Mild conditions (1 M guanidinium-HCl), temperature and point mutations within the RSL are the factors that induce polymerisation. Initiation of this process has been associated with the disruption of a salt bridge Glu342-»Lys290. In this paper the interaction of guani- dinium ion with Glu342 and Lys290 as well as the effect of this interaction on the mobility of RSL is studied by molecular modelling.