The PTS L-Ascorbate (L-Asc) Family (TC# 4.A.7) includes porters specific for L-ascorbate, and is part of the PTS-AG superfamily. A single PTS permease of the L-Asc family of PTS permeases has been functionally characterized. This is the SgaTBA system, renamed UlaABC (utilization of L-ascorbate) by Yew and Gerlt.[1][2]
| Phosphotransferase permease | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Identifiers | |||||||||
| Symbol | PTS | ||||||||
| Pfam | PF03611 | ||||||||
| InterPro | IPR004703 | ||||||||
| TCDB | 4.A.7 | ||||||||
| OPM superfamily | 426 | ||||||||
| OPM protein | 5zov | ||||||||
| |||||||||
The SgaTBA System
editThe SgaTBA permease consists of three proteins: SgaT, SgaB, and SgaA. SgaT is a 12 TMS protein, possibly very distantly related to the MFS hexuronate permease of Escherichia coli (TC# 2.A.1.14.2), which presumably functions as a PTS IIC protein.[3][4] This gene product, as well as SgaB and SgaA, are all essential for anaerobic L-ascorbate utilization, transport and phosphorylation.[5] This is the first documented example where the two sugar-specific energy-coupling proteins of a PTS permease are more closely related to the proteins of two different families. The sga regulation is controlled by the nearby YjfQ repressor.[5][6]
Homology
editHomologues of SgaT, like other PTS protein homologues, have been identified in a large number of evolutionarily divergent bacteria, but not in archaea or eukaryotes.[5] Bacteria that encode SgaT homologues include numerous Gram-negative Pseudomonadota, as well as many low and high G+C Gram-positive bacteria. Except for species of Corynebacterium, Streptomyces, and Bacillus, almost all organisms possessing SgaTBA homologues are human/animal pathogens.
Several organisms have two or more SgaT paralogues, including E. coli, which has three. In some of the homologues found in other bacteria, SgaB domains are fused C-terminal to the SgaT domains. For example, this is true of putative transporters in Vibrio cholerae, Pasteurella multocida and Mycoplasma pulmonis. Homologues of SgaB and SgaA, but not SgaT, are also found in transcriptional activator proteins where they function in regulation rather than sugar transport.[7]
Transport Reaction
editThe group translocation reaction catalyzed by SgaTBA is:
- L-ascorbate (out) → L-ascorbate-6-phosphate (in)
References
edit- ^ Tchieu JH, Norris V, Edwards JS, Saier MH (July 2001). "The complete phosphotransferase system in Escherichia coli". Journal of Molecular Microbiology and Biotechnology. 3 (3): 329–46. PMID 11361063.
- ^ Yew WS, Gerlt JA (January 2002). "Utilization of L-ascorbate by Escherichia coli K-12: assignments of functions to products of the yjf-sga and yia-sgb operons". Journal of Bacteriology. 184 (1): 302–6. doi:10.1128/jb.184.1.302-306.2002. PMC 134747. PMID 11741871.
- ^ Luo P, Yu X, Wang W, Fan S, Li X, Wang J (March 2015). "Crystal structure of a phosphorylation-coupled vitamin C transporter". Nature Structural & Molecular Biology. 22 (3): 238–41. doi:10.1038/nsmb.2975. PMID 25686089. S2CID 9955621.
- ^ Luo P, Dai S, Zeng J, Duan J, Shi H, Wang J (2018). "Inward-facing conformation of l-ascorbate transporter suggests an elevator mechanism". Cell Discovery. 4: 35. doi:10.1038/s41421-018-0037-y. PMC 6048161. PMID 30038796.
- ^ a b c Zhang Z, Aboulwafa M, Smith MH, Saier MH (April 2003). "The ascorbate transporter of Escherichia coli". Journal of Bacteriology. 185 (7): 2243–50. doi:10.1128/jb.185.7.2243-2250.2003. PMC 151508. PMID 12644495.
- ^ Campos E, Aguilar J, Baldoma L, Badia J (November 2002). "The gene yjfQ encodes the repressor of the yjfR-X regulon (ula), which is involved in L-ascorbate metabolism in Escherichia coli". Journal of Bacteriology. 184 (21): 6065–8. doi:10.1128/jb.184.21.6065-6068.2002. PMC 135402. PMID 12374842.
- ^ Greenberg DB, Stülke J, Saier MH (October 2002). "Domain analysis of transcriptional regulators bearing PTS regulatory domains". Research in Microbiology. 153 (8): 519–26. doi:10.1016/s0923-2508(02)01362-1. PMID 12437213.
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