Using a collection of nonfunctional missense mutants in the β-galactosidase and catechol 2,3-dioxygenase enzymes to better understand the complexity of protein folding

Abstract

Missense mutants can have devastating effects on proteins and usually act by causing perturbations in the folding of the protein that affects their final tertiary or quaternary forms. In order to better understand how missense mutants affect protein structure, a set of randomly generated nonfunctional missense mutants were isolated in two well-characterized enzymes, β-galactosidase and catechol 2,3-dioxygenase. This collection of missense mutants yielded important information regarding the key structural elements within correctly folded proteins and the ability of protein predictive tools to predict the effects of missense mutants. Many of the missense mutants were found to be salt-correctible and the rescuability of the missense mutants by various salts correlated with the Hofmeister series of ions that affect protein stability. In an additional study the promiscuous or broad-acting sumA glyV tRNA Gly3(GAU/C) missense suppressor that can recognize GAU or GAC aspartic acid codons and insert a glycine amino acid instead of aspartic acid was characterized.