Lyon William R, Caparon Michael G
Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri 63110-1093, USA.
Infect Immun. 2004 Mar;72(3):1618-25. doi: 10.1128/IAI.72.3.1618-1625.2004.
The serine protease HtrA is involved in the folding and maturation of secreted proteins, as well as in the degradation of proteins that misfold during secretion. Depletion of HtrA has been shown to affect the sensitivity of many organisms to thermal and environmental stresses, as well as being essential for virulence in many pathogens. In the present study, we compared the behaviors of several different HtrA mutants of the gram-positive pathogen Streptococcus pyogenes (group A streptococcus). Consistent with prior reports, insertional inactivation of htrA, the gene that encodes HtrA, resulted in a mutant that grew poorly at 37 degrees C. However, an identical phenotype was observed when a similar polar insertion was placed immediately downstream of htrA in the streptococcal chromosome, suggesting that the growth defect of the insertion mutant was not a direct result of insertional inactivation of htrA. This conclusion was supported by the observation that a nonpolar deletion mutation of htrA did not produce the growth defect. However, this mutation did affect the production of several secreted virulence factors whose biogenesis requires extensive processing. For the SpeB cysteine protease, the loss of HtrA was associated with a failure to proteolytically process the zymogen to an active protease. For the streptolysin S hemolysin, a dramatic increase in hemolytic activity resulted from the depletion of HtrA. Interestingly, HtrA-deficient mutants were not attenuated in a murine model of subcutaneous infection. These data add to the growing body of information that implies an important role for HtrA in the biogenesis of secreted proteins in gram-positive bacteria.
丝氨酸蛋白酶HtrA参与分泌蛋白的折叠与成熟过程，同时也参与降解分泌过程中错误折叠的蛋白质。研究表明，HtrA的缺失会影响许多生物体对热应激和环境应激的敏感性，并且对许多病原体的毒力至关重要。在本研究中，我们比较了革兰氏阳性病原体化脓性链球菌（A组链球菌）几种不同HtrA突变体的行为。与先前的报道一致，编码HtrA的基因htrA发生插入失活会导致突变体在37℃下生长不良。然而，当在链球菌染色体上htrA的紧邻下游进行类似的极性插入时，观察到了相同的表型，这表明插入突变体的生长缺陷并非htrA插入失活的直接结果。htrA的非极性缺失突变未产生生长缺陷这一观察结果支持了这一结论。然而，该突变确实影响了几种分泌性毒力因子的产生，这些毒力因子的生物合成需要广泛的加工过程。对于SpeB半胱氨酸蛋白酶，HtrA的缺失导致无法将酶原蛋白水解加工成活性蛋白酶。对于链球菌溶血素S，HtrA的缺失导致溶血活性显著增加。有趣的是，在皮下感染的小鼠模型中，HtrA缺陷型突变体并未减毒。这些数据进一步丰富了相关信息，表明HtrA在革兰氏阳性菌分泌蛋白的生物合成中发挥重要作用。
