Solution Structure of the Mycobacterium tuberculosis EsxG·EsxH Complex

Abstract

Mycobacterium tuberculosis encodes five type VII secretion systems that are responsible for exporting a number of proteins, including members of the Esx family, which have been linked to tuberculosis pathogenesis and survival within host cells. The gene cluster encoding ESX-3 is regulated by the availability of iron and zinc, and secreted protein products such as the EsxG·EsxH complex have been associated with metal ion acquisition. EsxG and EsxH have previously been shown to form a stable 1:1 heterodimeric complex, and here we report the solution structure of the complex, which features a core four-helix bundle decorated at both ends by long, highly flexible, N- and C-terminal arms that contain a number of highly conserved residues. Despite clear similarities in the overall backbone fold to the EsxA·EsxB complex, the structure reveals some striking differences in surface features, including a potential protein interaction site on the surface of the EsxG·EsxH complex. EsxG·EsxH was also found to contain a specific Zn2+ binding site formed from a cluster of histidine residues on EsxH, which are conserved across obligate mycobacterial pathogens including M. tuberculosis and Mycobacterium leprae. This site may reflect an essential role in zinc ion acquisition or point to Zn2+-dependent regulation of its interaction with functional partner proteins. Overall, the surface features of both the EsxG·EsxH and the EsxA·EsxB complexes suggest functions mediated via interactions with one or more target protein partners.

Structure of EspB, a secreted substrate of the ESX-1 secretion system of Mycobacterium tuberculosis

“…4A). While this C-terminal segment is flexible in the NMR structures of WxG100 proteins (Renshaw et al, 2005; Ilghari et al, 2011), it adopts a helical conformation in a number of crystal structures, including M. smegmatis EsxG–EsxH (PDB: 3Q4H), M. tuberculosis EsxO–EsxP (PDB: 3OGI and 4GZR) and M. tuberculosis EsxA–EsxB (PDB: 3FAV) (Arbing et al, 2013; Poulsen et al, 2014). Likewise, the YxxxD/E motif of PE25 is in a helical conformation in the PE25–PP41–EspG 5 structures (PDB: 4KXR and 4W4L) (Korotkova et al, 2014; Ekiert and Cox, 2014), although it is partially disordered in the structures of the PE25–PPE41 heterodimer (PDB: 2G38 and 4W4K) (Strong et al, 2006; Ekiert and Cox, 2014).…”

Mechanism of ESAT-6 membrane interaction and its roles in pathogenesis of Mycobacterium tuberculosis

“…This is evidenced by the fact that ESAT-6 and CFP-10 are secreted in a co-dependent manner, and the anti-parallel four-helix bundle of the heterodimer and the C-terminal Y-XXX-D/E secretion motif of CFP-10 are the common characteristics shared by the substrates of Type VII secretion system (Atmakuri and Fortune, 2008; Fortune et al, 2005; E. N. G. Houben et al, 2014; Lightbody et al, 2008; 2004; Renshaw et al, 2005; 2002; Veverka and Muskett, 2011). …”

Metallobiology of Tuberculosis

“…The number of Zn containing proteins identified in mycobacteria has increased significantly as more protein structures are resolved. Zn is part of M. tuberculosis zinc-metallopeptidases (33, 34), carbonic anhydrase (35), fructose biphosphate aldolase Fba (36), the helicase RqlH (37), the cytidine deaminase Cda (38), the MshC ligase involved in mycothiol biosynthesis (39), the 2C-methyl-D-erythritol-2,4-cyclodiphosphate synthase IspF (40), the 2-isopropylmalate synthase LeuA involved in leucine biosynthesis (41), the superoxide dismutase (SOD) SodC (42, 43), the Esx-3 substrate EsxG-EsxH complex (44), the inositol 1-phosphate synthase (45), the RecA intein (46) and several more.…”