Design of Ca2+‐independent Staphylococcus aureus sortase A mutants

Abstract The catalytic activity of Staphylococcus aureus sortase A (SaSrtA) is dependent on Ca 2+ , because binding of Ca 2+ to Glu residues distal to the active site stabilizes the substrate binding site. To obtain Ca 2+ ‐independent SaSrtA, we substituted two Glu residues in the Ca 2+ ‐binding pocket (Glu 105 and Glu 108 ). Although single mutations decreased SaSrtA activity, mutations of both Glu 105 and Glu 108 resulted in Ca 2+ ‐independent activity. Kinetic analysis suggested that the double mutations affect the substrate binding site, without affecting substrate specificity. This approach will allow us to develop SaSrtA variants suitable for various applications, including in vivo site‐specific protein modification and labeling. Biotechnol. Bioeng. 2012; 109: 2955–2961. © 2012 Wiley Periodicals, Inc.