Substrate-Assisted Catalysis Unifies Two Families of Chitinolytic Enzymes

Hen egg-white lysozyme has long been the paradigm for enzymatic glycosyl hydrolysis with retention of configuration, with a protonated carboxylic acid and a deprotonated carboxylate participating in general acid-base catalysis. In marked contrast, the retaining chitin degrading enzymes from glycosyl hydrolase families 18 and 20 all have a single glutamic acid as the catalytic acid but lack a nucleophile on the enzyme. Both families have a catalytic (βα)8-barrel domain in common. X-ray structures of three different chitinolytic enzymes complexed with substrates or inhibitors identify a retaining mechanism involving a protein acid and the carbonyl oxygen atom of the substrate’s C2 N-acetyl group as the nucleophile. These studies unambiguously demonstrate the distortion of the sugar ring toward a sofa conformation, long postulated as being close to that of the transition state in glycosyl hydrolysis.

Risk attitudes and migration decisions

Abstract This paper analyzes the relationship between individuals' attitudes towards risk and their decision to migrate. We consider migration in the United States across metropolitan statistical areas (MSAs) between 1997 and 2015, based on data from the Panel Study of Income Dynamics (PSID). Using random‐effects specifications, we find that being relatively more willing to take risks is positively and significantly related to cross‐MSA migration. For cross‐state migration and migration across larger distances, risk attitudes are slightly more important. A recursive bivariate probit model of simultaneous equations addresses the potential endogenous nature of attitudes towards risk and allows ruling out reverse causality