Structure and Function of Neisseria gonorrhoeae MtrF Illuminates a Class of Antimetabolite Efflux Pumps

Abstract

SUMMARY Neisseria gonorrhoeae is an obligate human pathogen and the causative agent of the sexually-transmitted disease gonorrhea. The control of this disease has been compromised by the increasing proportion of infections due to antibiotic-resistant strains, which are growing at an alarming rate. N. gonorrhoeae MtrF is an integral membrane protein, which belongs to the AbgT family of transporters for which no structural information is available. Here we describe the crystal structure of MtrF, revealing a dimeric molecule with architecture distinct from all other families of transporters. MtrF is a bowl-shaped dimer with a solvent-filled basin extending from the cytoplasm to halfway across the membrane bilayer. Each subunit of the transporter contains nine transmembrane helices and two hairpins, posing a plausible pathway for substrate transport. A combination of the crystal structure and biochemical functional assays suggests that MtrF is an antibiotic efflux pump, mediating bacterial resistance to sulfonamide antimetabolite drugs.

The bacterial dicarboxylate transporter VcINDY uses a two-domain elevator-type mechanism

“…These transporters include the human Na + P i transporter, NaPi-II 36 ; and two recently structurally characterized representatives from the p-aminobenzoyl-glutamate transporter (AbgT) family, YdaH and MtrF 22,37,38 . The DASS family, to which VcINDY belongs, and the AbgT family, are both members of the Ion Transporter (IT) superfamily, strongly indicating that the elevator-type movement is a common mechanism for all IT superfamily members.…”

Shared Molecular Mechanisms of Membrane Transporters

“…Elevator-like structural transitions have also been proposed for phosphorylation-coupled saccharide transporters (20), a structurally distinct phosphorylation-coupled vitamin C transporter (21), the sodium-dicarboxylate symporter vcINDY (22,23), and citrate transporter (24). Finally, several other transporters have architectural features highly suggestive of an elevator mechanism, including concentrative nucleoside transporters (25) and transporters of the AbgT family (26,27). In the elevator alternating-access mechanism, the substrate-binding site is confined largely, or entirely, to a single domain that traverses the membrane along a relatively rigid, immobile scaffold domain.…”

“…The position of the ion-binding site ( pink) and the ion permeation pathways in a lipid bilayer are shown. Adapted with permission from Reference 19. symporter vcCNT (25), and p-aminobenzoyl-glutamate AbgT transporters (26,27). All three families architecturally resemble Glt Ph and SeCitS: They are either dimers (vcINDY and AbgT transporters) or trimers (vcCNT) that consist of a central oligomerization domain and peripheral bundle or transport domains that contain the substrate-binding sites.…”

Comparative Analyses of Transport Proteins Encoded within the Genomes of Bdellovibrio bacteriovorus HD100 and Bdellovibrio exovorus JSS

“…This latter has been reported to play a role in cell wall hydrolysis, possibly by regulating murein hydrolase export. A combination of the crystal structure and biochemical functional assays suggests that MtrF is an antibiotic efflux pump mediating bacterial resistance to sulfonamide antimetabolite drugs [Su et al, 2015]. Ferroportin is an iron-regulated transporter in mammals [Delaby et al, 2008].…”