Replacement of histidine 340 with alanine inactivates the group A Streptococcus extracellular cysteine protease virulence factor

Streptococcus pyogenes expresses a highly conserved extracellular cysteine protease that is a virulence factor for invasive disease, including soft ti ssue infection. Site-directed mutagenesis was used to generate a His340Ala recombinant mutant protein that was made as a stable 40-kDa zymogen by Esch erichia coli, Purified His340Ala protein was proteolytically inactive when bovine casein and human fibronectin were used as substrates, Wild-type 28-k Da streptococcal protease purified from S, pyogenes processed the 40-kDa mu tant zymogen to a 28-kDa mature form, a result suggesting that the derivati ve protein retained structural integrity. The data are consistent with the hypothesis that His340 is an enzyme active site residue, an idea confirmed by recent solution of the zymogen crystal structure (T. F, Kagawa, J, C, Co oney, H, M. Baker, S, McSweeney, M, Liu, S, Gubba, J, M. Musser, and E, N, Baker, Proc. Natl, Acad, Sci, USA 97:2235-2240, 2000), The data provide add itional insight into structure-function relationships in this S. pyogenes v irulence factor.