biostudies-literatureUnknown102(4)Haddad KCalpha-Lytic protease is a bacterial serine protease widely studied as a model system of enzyme catalysis. Here we report that lyophilization induces a structural change in the enzyme that is not reversed by redissolution in water. The structural change reduces the mobility of the active-site histidine residue and the catalytic activity of the enzyme. The application of mild pressure to solutions of the altered enzyme reverses the lyophilization-induced structural change and restores the mobility of the histidine residue and the enzyme's catalytic activity. This effect of lyophilization permits a unique opportunity for investigating the relationship between histidine ring dynamics and catalytic activity. The results demonstrate that His57 in resting enzymes is more mobile than previously thProceedings of the National Academy of Sciences of the United States of America1006-11https://www.ebi.ac.uk/biostudies/studies/S-EPMC545854biostudies-literaturealpha-lytic protease can exist in two separately stable conformations with different His57 mobilities and catalytic activities.PMC545854Sudmeier JLHaddad KCBachovchin DABachovchin WWfalsealpha-lytic protease can exist in two separately stable conformations with different His57 mobilities and catalytic activities.alpha-Lytic protease is a bacterial serine protease widely studied as a model system of enzyme catalysis. Here we report that lyophilization induces a structural change in the enzyme that is not reversed by redissolution in water. The structural change reduces the mobility of the active-site histidine residue and the catalytic activity of the enzyme. The application of mild pressure to solutions of the altered enzyme reverses the lyophilization-induced structural change and restores the mobility of the histidine residue and the enzyme's catalytic activity. This effect of lyophilization permits a unique opportunity for investigating the relationship between histidine ring dynamics and catalytic activity. The results demonstrate that His57 in resting enzymes is more mobile than previously th2005-01-01T00:00:00Z2005 Jan2025-04-20T01:35:37.785Z2019-03-27T01:08:32ZS-EPMC5458541565713410.1073/pnas.0409279102