The crystal structure of an essential high-temperature requirement protein HtrA1 (Rv1223) from Mycobacterium tuberculosis reveals its unique features

Abstract

High-temperature requirement A (HtrA) proteins, which are members of the heat-shock-induced serine protease family, are involved in extracytoplasmic protein quality control and bacterial survival strategies under stress conditions, and are associated with the virulence of several pathogens; they are therefore major drug targets. Mycobacterium tuberculosis possesses three putative HtrAs: HtrA1 (Rv1223), HtrA2 (Rv0983) and HtrA3 (Rv0125). Each has a cytoplasmic region, a transmembrane helix and a periplasmic region. Here, the crystal structure of the periplasmic region consisting of a protease domain (PD) and a PDZ domain from an M. tuberculosis HtrA1 mutant (mHtrA1) is reported at 2.7 Å resolution. Although the mHtrA1 PD shows structural features similar to those of other HtrAs, its loops, particularly L3 and LA, display different conformations. Loop L3 communicates between the PDs of the trimer and the PDZ domains and undergoes a transition from an active to an inactive conformation, as reported for an equivalent HtrA (DegS). Loop LA, which is responsible for higher oligomer formation owing to its length (50 amino acids) in DegP, is very short in mHtrA1 (five amino acids), as in mHtrA2 (also five amino acids), and therefore lacks essential interactions for the formation of higher oligomers. Notably, a well ordered loop known as the insertion clamp in the PDZ domain interacts with the protease domain of the adjacent molecule, which possibly aids in the stabilization of a trimeric functional unit of this enzyme. The three-dimensional structure of mHtrA1 presented here will be useful in the design of enzyme-specific antituberculosis inhibitors.

The crystal structure of Mycobacterium tuberculosis high-temperature requirement A protein reveals an autoregulatory mechanism

“…While the expression constructs for the periplasmic domain are broadly similar, the authors reported that this protein was a trimer in solution. Owing to issues with autoproteolysis and/or degradation, the structure that was determined was that of an active-site mutant (Singh et al, 2018). The structure of the active enzyme described here at higher resolution (1.83 Å ) also reveals a few differences from the previous report.…”

“…While this manuscript was being compiled for peer review, the structure of M. tuberculosis ÁTM HtrA was reported (Singh et al, 2018). In their manuscript, Singh and coworkers described the crystal structure of M. tuberculosis HtrA determined at 2.7 Å resolution (PDB entry 5zvj).…”

Pneumococcal Extracellular Serine Proteases: Molecular Analysis and Impact on Colonization and Disease

“…The molecular analysis of different HtrA serine proteases of other pathogenic bacteria via multiple sequence alignment (MSA) revealed a sequence similarity, especially in the functional protease and PDZ domains, as reviewed more extensively elsewhere (Backert et al, 2018;Boehm et al, 2018;Singh et al, 2018). They are widely distributed in many bacterial species such as Escherichia coli, Legionella fallonii, Thermotoga maritima, and Mycobacterium tuberculosis (Kim et al, 2003;Bai et al, 2011;Malet et al, 2012;Cortes et al, 2013;Chang, 2016;Singh et al, 2018).…”

“…Bacterial HtrA is a heat-shock-induced serine protease that displays a multifunctional role like protein quality control and bacterial survival under different stress conditions such as oxidative and heat stress ( Sebert et al., 2002 ; Singh et al., 2018 ). For instance, HtrA protease in Lactococcus is considered as a housekeeping protease ( Poquet et al., 2000 ), while in other bacteria, HtrA prevents the cell from the cytotoxicity of misfolded proteins by refolding or degrading them ( Clausen et al., 2002 ; Zarzecka et al., 2019 ).…”

“…Finally, the PDZ domain (abbreviation combining letters of the first three proteins discovered to share this domain, postsynaptic density protein, Drosophila discs large tumor suppressor, and zonula occludens-1) is located at the C-terminal end. HtrA in other bacterial species contains one or more PDZ domain(s) ( Fan et al., 2011 ; Backert et al., 2018 ; Singh et al., 2018 ). In some situations, such as protein-protein interactions, the HtrA-PDZ domain acts as a protein folding stress sensor and controls the pyrolytic activity ( Murwantoko et al., 2004 ; Wilken et al., 2004 ; Hasselblatt et al., 2007 ).…”