Localization and mutagenesis of the sorting signal binding site on sortase A from Staphylococcus aureus

Abstract
Surface proteins in Gram‐positive bacteria are anchored to the cell wall by the action of sortase enzymes. The Staphylococcus aureus sortase A (SrtA) protein anchors proteins by recognizing a cell wall sorting signal containing the amino acid sequence LPXTG. To understand how SrtA binds this sequence, we carried out NMR studies of new peptidyl‐cyanoalkene and peptidyl‐sulfhydryl inhibitors that contain the sorting signal sequence LPAT. These studies combined with amino acid mutagenesis identified a catalytically important and conserved binding surface formed by residues A118, T180, and I182. Compatible with its recently proposed role as a general base, R197 is also shown to be required for catalysis.