Delving into the details: Investigation of the kinetic properties of SpeG Spermidine N ‐acetyltransferases from Escherichia coli and Vibrio cholerae

Biofilms are communities of bacteria found in a variety of environments, including the intestinal mucosa of humans and on surfaces of medical devices. These biofilms protect bacteria from antibiotics and other adverse environmental stresses. Polyamines are polycationic small molecules that are involved in biofilm formation. When polyamines are acetylated, biofilm formation increases. One enzyme that acetylates polyamines in bacteria is the spermidine N‐ acetyltransferase SpeG. This enzyme is important for regulating polyamine levels and responding to bacterial stress conditions, but its role in biofilm formation is still unknown. We previously determined the structures of the SpeG enzymes from Vibrio cholerae (VcSpeG) and Escherichia coli (EcSpeG) , and found they exist as dodecamers and posses an allosteric site where polyamines bind. This site is not found in the human spermine/spermidine acetyltransferase (SSAT) enzyme, but they share a common core Gcn5‐related N‐ acetyltransferase scaffold. These structural differences provide a unique opportunity to study the effect of the allosteric site on enzyme activity and regulation of polyamine levels in different organisms. As a first step toward elucidating the functional properties of SpeG, we present the kinetic characterization and comparison of VcSpeG and EcSpeG enzymes and show how they exhibit distinct properties between the two organisms and the human SSAT enzyme. Additionally, we present a structural comparison of the three enzymes to provide insight into their kinetic differences. Understanding the kinetic details of SpeG polyamine acetylation will ultimately provide important insight for designing drugs that specifically target SpeG over the human SSAT enzyme to prevent or reduce biofilm formation and pathogenesis. Support or Funding Information Startup funds to MLK from San Francisco State University