Identifiers
SymbolAbgT
PfamPF03806
TCDB2.A.68
OPM superfamily272
OPM protein4r1i
Available protein structures:
Pfam  structures / ECOD  
PDBRCSB PDB; PDBe; PDBj
PDBsumstructure summary

The p-aminobenzoyl-glutamate transporter (AbgT) family (TC# 2.A.68) is a family of transporter proteins belonging to the ion transporter (IT) superfamily.[1][2] The AbgT family consists of the AbgT (YdaH; TC# 2.A.68.1.1) protein of E. coli and the MtrF drug exporter (TC# 2.A.68.1.2) of Neisseria gonorrhoeae.[3][4] The former protein is apparently cryptic in wild-type cells, but when expressed on a high copy number plasmid, or when expressed at higher levels due to mutation, it appeared to allow uptake (Km = 123 nM; see Michaelis–Menten kinetics) and subsequent utilization of p-aminobenzoyl-glutamate as a source of p-aminobenzoate for p-aminobenzoate auxotrophs.[5] p-Aminobenzoate is a constituent of and a precursor for the biosynthesis of folic acid. MtrF was annotated as a putative drug efflux pump.[4]

Structure

AbgT is 510 amino acyl residues long and has 12-13 putative transmembrane α-helical spanners (TMSs). MtrF is 522 aas long and has 11 or 12 putative TMSs. The 3-d structures of MtrF and a YdaH homologue have been solved, and functional studies show that it is a drug exporter. The 3-d structure shows that it has 9 TMSs with hairpin entry loops.[6]

Crystal Structures:

Genetics

The abgT gene is preceded by two genes, abgA and abgB, which code for homologous amino acyl amino hydrolases and hydrolyze p-aminobenzoyl glutamate to p-aminobenzoate and glutamate.[5] Because of the structural similarity of p-aminobenzoyl-glutatmate to peptides, and the enzymatic activities of the abgA and abgB gene products, it has been suggested that AbgT is also a peptide transporter.[5] Demonstration of an energy requirement suggested an H+-dependent mechanism.[5] Expression of these genes is regulated by AbgR and an unknown effector.

Function

As noted above, the AbgT family of transporters has been thought to contribute to bacterial folate biosynthesis by importing the catabolite p-aminobenzoyl-glutamate for producing folate. Approximately 13,000 putative family members were identified in 2015.[7] The X-ray structures of the full-length Alcanivorax borkumensis YdaH (AbgT) and Neisseria gonorrhoeae MtrF proteins. The structures revealed that these two transporters assemble as dimers with architectures distinct from all other families of transporters for which 3-d structures were available.[8] Both YdaH and MtrF are bowl-shaped dimers with a solvent-filled basin extending from the cytoplasm halfway across the membrane bilayer. The protomers of YdaH and MtrF contain nine transmembrane helices and two hairpins which suggested a plausible pathway for substrate transport.[7] A combination of the crystal structure, genetic analyses and substrate accumulation assays indicated that both YdaH and MtrF behave as exporters, capable of removing the folate metabolite p-aminobenzoic acid from bacterial cells. In fact, it was shown that both YdaH and MtrF participate as antibiotic efflux pumps, mediating bacterial resistance to sulfonamide antimetabolite drugs. Possibly, many AbgT-family transporters act as exporters, conferring resistance to sulfonamides.[7]

Transport reaction

The generalized transport reaction initially proposed for AbgT is:

p-aminobenzoyl-glutamate (out) + nH+ (out) → p-aminobenzoyl-glutamate (in) + nH+ (in)

but the more recently proposed transport reaction is:

Sulfonamide drugs (in) + H+ (out) → Sulfonamide drugs (out) + H+ (in)

See also

References

  1. ↑ Prakash S, Cooper G, Singhi S, Saier MH (December 2003). "The ion transporter superfamily". Biochimica et Biophysica Acta (BBA) - Biomembranes. 1618 (1): 79–92. doi:10.1016/j.bbamem.2003.10.010. PMID 14643936.
  2. ↑ Rabus R, Jack DL, Kelly DJ, Saier MH (December 1999). "TRAP transporters: an ancient family of extracytoplasmic solute-receptor-dependent secondary active transporters". Microbiology. 145 ( Pt 12) (12): 3431–45. doi:10.1099/00221287-145-12-3431. PMID 10627041.
  3. ↑ Hussein MJ, Green JM, Nichols BP (December 1998). "Characterization of mutations that allow p-aminobenzoyl-glutamate utilization by Escherichia coli". Journal of Bacteriology. 180 (23): 6260–8. doi:10.1128/JB.180.23.6260-6268.1998. PMC 107711. PMID 9829935.
  4. 1 2 Folster JP, Shafer WM (June 2005). "Regulation of mtrF expression in Neisseria gonorrhoeae and its role in high-level antimicrobial resistance". Journal of Bacteriology. 187 (11): 3713–20. doi:10.1128/JB.187.11.3713-3720.2005. PMC 1112036. PMID 15901695.
  5. 1 2 3 4 Carter EL, Jager L, Gardner L, Hall CC, Willis S, Green JM (May 2007). "Escherichia coli abg genes enable uptake and cleavage of the folate catabolite p-aminobenzoyl-glutamate". Journal of Bacteriology. 189 (9): 3329–34. doi:10.1128/JB.01940-06. PMC 1855889. PMID 17307853.
  6. ↑ Su CC, Bolla JR, Kumar N, Radhakrishnan A, Long F, Delmar JA, Chou TH, Rajashankar KR, Shafer WM, Yu EW (April 2015). "Structure and function of Neisseria gonorrhoeae MtrF illuminates a class of antimetabolite efflux pumps". Cell Reports. 11 (1): 61–70. doi:10.1016/j.celrep.2015.03.003. PMC 4410016. PMID 25818299.
  7. 1 2 3 Delmar JA, Yu EW (February 2016). "The AbgT family: A novel class of antimetabolite transporters". Protein Science. 25 (2): 322–37. doi:10.1002/pro.2820. PMC 4815354. PMID 26443496.
  8. ↑ Bolla JR, Su CC, Delmar JA, Radhakrishnan A, Kumar N, Chou TH, Long F, Rajashankar KR, Yu EW (April 2015). "Crystal structure of the Alcanivorax borkumensis YdaH transporter reveals an unusual topology". Nature Communications. 6: 6874. Bibcode:2015NatCo...6.6874B. doi:10.1038/ncomms7874. PMC 4410182. PMID 25892120.
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