PMID:11566984

Citation	Krom, BP, Aardema, R and Lolkema, JS (2001) Bacillus subtilis YxkJ is a secondary transporter of the 2-hydroxycarboxylate transporter family that transports L-malate and citrate. J. Bacteriol. 183:5862-9
Abstract	The genome of Bacillus subtilis contains two genes that code for membrane proteins that belong to the 2-hydroxycarboxylate transporter family. Here we report the functional characterization of one of the two, yxkJ, which codes for a transporter protein named CimHbs. The gene was cloned and expressed in Escherichia coli and complemented the citrate-negative phenotype of wild-type E. coli and the malate-negative phenotype of the E. coli strain JRG4008, which is defective in malate uptake. Subsequent uptake studies in whole cells expressing CimHbs clearly demonstrated the citrate and malate transport activity of the protein. Immunoblot analysis showed that CimHbs is a 48-kDa protein that is well expressed in E. coli. Studies with right-side-out membrane vesicles demonstrated that CimHbs is an electroneutral proton-solute symporter. No indications were found for the involvement of Na(+) ions in the transport process. Inhibition of the uptake catalyzed by CimHbs by divalent metal ions, together with the lack of effect on transport by the chelator EDTA, showed that CimHbs translocates the free citrate and malate anions. Among a large set of substrates tested, only malate, citramalate, and citrate competitively inhibited citrate transport catalyzed by CimHbs. The transporter is strictly stereoselective, recognizing only the S enantiomers of malate and citramalate. Remarkably, though citramalate binds to the transporter, it is not translocated.
Links	PubMed PMC99663 Online version:10.1128/JB.183.20.5862-5869.2001
Keywords	Bacillus subtilis/genetics; Bacillus subtilis/metabolism; Bacterial Proteins; Biological Transport, Active; Carrier Proteins/antagonists & inhibitors; Carrier Proteins/genetics; Carrier Proteins/metabolism; Cations, Monovalent; Citric Acid/metabolism; Malates/metabolism; Membrane Proteins/antagonists & inhibitors; Membrane Proteins/genetics; Membrane Proteins/metabolism; Membrane Transport Proteins; Membranes/metabolism; Proton-Motive Force; Protons; Sodium/metabolism; Substrate Specificity
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
BACSU:CIMH		GO:0015531: citrate:proton symporter activity	ECO:0000314:		F		Figure 2A, 3 - shows that production of the gene product CimHbs due to the normal function of the CimH gene causes greater catalysis of citrate and malate uptake.	complete CACAO 11116

References

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