An Allosteric Site Residue Critical for Transmission of the Allosteric Signal of the Vibrio cholerae SpeG Enzyme

Abstract

SpeG is a polyamine N‐acetyltransferase enzyme that belongs to the superfamily of Gcn5‐related N‐acetyltransferases (GNATs). We previously showed this enzyme from Vibrio cholerae (VcSpeG) acetylates spermine and spermidine. SpeG is thought to contribute to biofilm formation in several pathogenic bacteria and several studies have shown that it also plays a role in bacterial polyamine homeostasis under stressful conditions. This GNAT is unique because it forms a dodecameric structure and has an allosteric site in each monomer. Additionally, it binds polyamines at both allosteric and active sites. Previous X‐ray crystallographic studies have shown that the E41 residue in the allosteric site of VcSpeG forms a hydrogen bond with N10 of spermine and N6 of spermidine. We hypothesized that mutating this residue would affect the allosteric network of the enzyme. Therefore, we created a series of E41 point mutations and investigated the enzymatic activity and kinetic parameters toward spermine and spermidine. Changing the identity of the residue at this location either increased the catalytic efficiency and altered the sigmoidicity of the substrate saturation curve or decreased the catalytic efficiency and affected cooperativity. This implies that the identity of the residue at this position affects the allosteric signal that is transmitted. Further investigation into other residues in this site is warranted.Support or Funding InformationResearch reported in this work was supported by the National Institute of General Medical Sciences of the National Institutes of Health under Award Number R35GM133506 (to MLK).