Structure and Function of the Virulence-Associated High-Temperature Requirement A of Mycobacterium tuberculosis

Abstract

The high-temperature requirement A (HtrA) family of serine proteases has been shown to play an important role in the environmental and cellular stress damage control system in Escherichia coli. Mycobacterium tuberculosis ( Mtb) has three putative HtrA-like proteases, HtrA1, HtrA2, and HtrA3. The deletion of htrA2 gives attenuated virulence in a mouse model of TB. Biochemical analysis reveals that HtrA2 can function both as a protease and as a chaperone. The three-dimensional structure of HtrA2 determined at 2.0 A resolution shows that the protease domains form the central core of the trimer and the PDZ domains extend to the periphery. Unlike E. coli DegS and DegP, the protease is naturally active due to the formation of the serine protease-like catalytic triad and its uniquely designed oxyanion hole. Both protease and PDZ binding pockets of each HtrA2 molecule are occupied by autoproteolytic peptide products and reveal clues for a novel autoregulatory mechanism that might have significant importance in HtrA-associated virulence of Mtb.

PepD Participates in the Mycobacterial Stress Response Mediated through MprAB and SigE

“…⌬pepD::Hyg r mutants of M. tuberculosis Erdman are altered for virulence in mice. In particular, ⌬pepD::Hyg r mutant-infected animals exhibit increased time to death, and infection by ⌬pepD::Hyg r mutants induces less tissue pathology than in animals infected with wild-type or complemented mutant derivatives (33). Taken together, these results suggest that PepD is required for aspects of M. tuberculosis adaptation within the host.…”

“…A subset of HtrA family members is also required for aspects of pathogenesis in both Gram-positive and Gramnegative organisms (14,16,45,49,57). M. tuberculosis possesses three HtrA-like proteases: Rv1223 (degP or htrA1), Rv0983 (pepD or htrA2), and Rv0215 (pepA or htrA3) (8,33), all of which share regions of sequence homology with one another. Initial studies of PepD and PepA in M. tuberculosis indicate that these proteins are secreted and are present within the culture filtrate (47).…”

“…Initial studies of PepD and PepA in M. tuberculosis indicate that these proteins are secreted and are present within the culture filtrate (47). More recently, PepD has been shown to possess both protease and chaperone activities (33); however, the biological activities of DegP and PepA remain unclear. ⌬pepD::Hyg r mutants of M. tuberculosis Erdman are altered for virulence in mice.…”

Distinct regulatory mechanisms balance DegP proteolysis to maintain cellular fitness during heat stress

“…At the position corresponding to residue 207 in E. coli DegP, many orthologs have a wild-type proline (Mohamedmohaideen et al 2008;Cezairliyan and Sauer 2009). Based on our results, any potential deleterious effects of this ''activating'' proline are likely to be balanced by one or more ''inactivating'' residues elsewhere in the structure.…”

Proteolytic activation of Chlamydia trachomatis HTRA is mediated by PDZ1 domain interactions with protease domain loops L3 and LC and beta strand β5

“…The activation mechanism of DegS (another E. coli member of the HtrA family) is less defined, as DegS appears to also be activated by a DegP-like 'PDZ -L3' interaction [23], although alternate structural studies suggest that the activation occurs upon direct detection of the substrate C-terminus via a 'C-terminus -L3' interaction [24]. The Mycobacterium tuberculosis HtrA2 protein (MtHtrA2) has only been shown to form trimers in solution and remains in a constantly activated state with its PDZ1 domain appearing to bind autoproteolysis products [25]. This mechanistic diversity within the HtrA family is remarkable considering their structural homogeneity [21].…”