Expression of the Staphylococcus aureus surface proteins HtrA1 and HtrA2 in Lactococcus lactis

Staphylococcus aureus encodes two HtrA-like serine surface proteases, called HtrA₁ and HtrA₂. The roles of these HtrA homologs were distinguished by expression studies in a heterologous host, Lactococcus lactis, whose single extracellular protease, HtrA_Ll, was absent. HtrA_Ll is involved in stress resistance, and processing and/or degradation of extracellular proteins. Controlled expression of staphylococcal htrA₁ and htrA₂ was achieved in L. lactis strain NZ9000 ΔhtrA, as confirmed with anti-HtrA₁ and anti-HtrA₂ specific antibodies. HtrA₁ fully restored thermo-resistance to the htrA-defective L. lactis strain, despite a poor capacity to degrade abnormal or truncated proteins. We therefore propose that activities of HtrA₁ other than proteolysis may be sufficient for high-temperature growth complementation. HtrA₂ is 36% identical to HtrA_Ll, and was highly expressed in L. lactis; nevertheless, it displayed nearly no detectable activities. The poor proteolytic activities of staphylococcal HtrA proteins in L. lactis may reflect a requirement for S. aureus-specific co-factors. [Copyright &y& Elsevier]