Biochemical properties of the HtrA homolog from bacterium Stenotrophomonas maltophilia

The HtrA proteins due to their proteolytic, and in many cases chaperone activity, efficiently counteract consequences of stressful conditions. In the environmental bacterium and nosocomial pathogen Stenotrophomonas maltophilia HtrA (HtrA.Sm) is induced as a part of adaptive response to host temperature (37. °C).We examined the biochemical properties of HtrA.Smand compared them with those of model HtrA.Ecfrom Escherichia coli. We found that HtrA.Smis a protease and chaperone that operates over a wide range of pH and is highly active at temperatures between 35 and 37. °C. The temperature-sensitive activity corresponded well with the lower thermal stability of the protein and weaker stability of the oligomer. Interestingly, the enzyme shows slightly different substrate cleavage specificity when compared to other bacterial HtrAs. A computational model of the three-dimensional structure of HtrA.Smindicates differences in the S1 substrate specificity pocket and suggests weaker inter-trimer interactions when compared to HtrA.Ec.The observed features of HtrA.Smsuggest that this protein may play a protective role under stressful conditions acting both as a protease and a chaperone. The optimal temperatures for the protein activity may reflect the evolutionary adaptation of S. maltophilia to life in soil or aqueous environments, where the temperatures are usually much below 37. °C.