Structural basis for a homodimeric ATPase subunit of an ECF transporter

Abstract

The transition metal cobalt, an essential cofactor for many enzymes in prokaryotes, is taken up by several specifi c transport systems. The CbiMNQO protein complex belongs to type-1 energy-coupling factor (ECF) transporters and is a widespread group of microbial cobalt transporters. CbiO is the ATPase subunit (A-component) of the cobalt transporting system in the gram-negative thermophilic bacterium Thermoanaerobacter tengcongensis. Here we report the crystal structure of a nucleotide-free CbiO at a resolution of 2.3 Å. CbiO contains an N-terminal canonical nucleotide-binding domain (NBD) and C-terminal helical domain. Structural and biochemical data show that CbiO forms a homodimer mediated by the NBD and the C-terminal domain. Interactions mainly via conserved hydrophobic amino acids between the two C-terminal domains result in formation of a four-helix bundle. Structural comparison with other ECF transporters suggests that non-conserved residues outside the T-component binding groove in the A component likely act as a specifi city determinant for T components. Together, our data provide information on understanding of the structural organization and interaction of the CbiMNQO system.

ATP binding drives substrate capture in an ECF transporter by a release-and-catch mechanism

“…Pre-incubation of the sample with the hydrolysis product MgADP did not have a detectable effect on the stability of the transporter complex. This result is consistent with the structural data, whereby the nucleotide-free and ADP bound states of the transporter adopt a similar ATPase-open conformation 10-12,25,34 with a 1:1:1:1 subunit stoichiometry 9 (Supplementary Fig. 1).…”

Diversity in ABC transporters: Type I, II and III importers

“…The dimerized structure of the EcfA–EcfA′ in the full length structures is similar to the structures of homodimer CbiO of CbiMNQO the cobalt EcfA–EcfA′ energy module from Thermoanaerobacter tengcongensis (Chai et al ., 2013 ) and EcfA–EcfA′ heterodimer structure from T. maritima (Karpowich & Wang, 2013 ). Similar to Type I and II transporters, the NBD is made up of a helical subdomain and RecA-like domain with the conserved motifs for ATP binding and hydrolysis.…”

The repertoire of ABC proteins in Clostridioides difficile

“…The absence of an SP in the import system is a unique feature for EFC-type ABC importers. It has been reported in S. Typhimurium that the uptake of cobalt from the ABC transporter is not dependent on an extracellular SP [92] , [93] . Also, the NP encoded from cd630_04310 and its TP encoded from cd630_04300 shared protein sequence homology to uncharacterized proteins involved in cobalt transport and energy ECF-type systems of many organisms.…”