Linked Domain Architectures Allow for Specialization of Function in the FtsK/SpoIIIE ATPases of ESX Secretion Systems

Abstract

Among protein secretion systems there are specialized ATPases that serve different functions such as substrate recognition, substrate unfolding, and assembly of the secretory machinery. ESX protein secretion systems require FtsK/SpoIIIE family ATPases but the specific function of these ATPases is poorly understood. The ATPases of ESX secretion systems have a unique domain architecture among proteins of the FtsK/SpoIIIE family. All well-studied FtsK family ATPases to date have one ATPase domain and oligomerize to form a functional molecular machine, most commonly a hexameric ring. In contrast, the ESX ATPases have three ATPase domains, either encoded by a single gene or by two operonic genes. It is currently unknown which of the ATPase domains is catalytically functional and whether each domain plays the same or a different function. Here we focus on the ATPases of two ESX systems, the ESX-1 system of Mycobacterium tuberculosis and the yuk system of Bacillus subtilis. We show that ATP hydrolysis by the ESX ATPase is required for secretion, suggesting that this enzyme at least partly fuels protein translocation. We further show that individual ATPase domains play distinct roles in substrate translocation and complex formation. Comparing the single chain and split ESX ATPases we reveal differences in the requirements of these unique secretory ATPases.

Substrates Control Multimerization and Activation of the Multi-Domain ATPase Motor of Type VII Secretion

“…Thus, although binding of ATP by ATPase 2 and ATPase 3 is required for full activity of EccC, these domains act to regulate the activity of ATPase 1 rather than additively contribute to overall ATPase activity. This is consistent with recent genetic evidence that the different ATPase domains play distinct roles during secretion in vivo (Ramsdell et al, 2014). …”

“…ATPase 1 has a completely conserved R- finger (Figure S4G and S4H) that is required for secretion in vivo (Figure S4I), implying that formation of the active site of ATPase 1 also involves multimerization. Furthermore, expression of ATPase-deficient versions of EccC in wild-type bacteria has a dominant- negative effect on secretion, consistent with this notion (Ramsdell et al, 2014). …”

The Enigmatic Esx Proteins: Looking Beyond Mycobacteria

“…The ATPase domain requirements for substrate translocation in Bacillus were 17 recently dissected in a study of domain-specific nucleotide binding and 18 hydrolysis [63]. Only one of the three ATPase domains of YukBA was 19 required for secretion in Bacillus, similar to that observed in ATPases from 20 some S. aureus strains [40].…”

Structural variability of EspG chaperones from mycobacterial ESX-1, ESX-3 and ESX-5 type VII secretion systems

“…The crystal structure of the heterotrimeric PE25-PPE41-EspG 5 protein complex revealed that EspG 5 interacts with a PE25-PPE41 heterodimer by binding to a hydrophobic patch at the tip of PPE41 [26,27]. The general YxxD/E secretion motif [28,29] at the distal end of PE25 is free to interact with the ESX-5 secretion machinery in the inner membrane, probably by interaction with the Ftsk/SpoIIIE-like ATPase EccC 5 [30,31]. In addition, EspG 5 was reported to improve solubility of aggregation-prone PE-PPE pairs upon co-expression [26,32].…”