kinact/KIValue Determination for Penicillin-Binding Proteins in Live Cells

Abstract

AbstractPenicillin-binding proteins (PBPs) are an essential family of bacterial enzymes that are inhibited by the β-lactam class of antibiotics. PBP inhibition disrupts cell wall biosynthesis, which results in deficient growth and proliferation, and ultimately leads to lysis. IC50values are often employed as descriptors of enzyme inhibition and inhibitor selectivity but can be misleading in the study of time-dependent, irreversible inhibitors. Due to this disconnect, the second order rate constantkinact/KIis a more appropriate metric of covalent inhibitor potency. Despite being the gold standard measurement of potency,kinact/KIvalues are typically obtained fromin vitroassays, which limits assay throughput if investigating an enzyme family with multiple homologs (such as the PBPs). Therefore, we developed a whole-cellkinact/KIassay to define inhibitor potency for the PBPs inStreptococcus pneumoniaeusing the fluorescent activity-based probe Bocillin-FL. Our results align within vitro kinact/KIdata and show a comparable relationship to previously established IC50values. These results support the validity of ourin vivo kinact/KImethod as a means of obtaining a full picture of β-lactam potency for a suite of PBPs.Abstract Figure