PMID:16331991

Citation	Borths, EL, Poolman, B, Hvorup, RN, Locher, KP and Rees, DC (2005) In vitro functional characterization of BtuCD-F, the Escherichia coli ABC transporter for vitamin B12 uptake. Biochemistry 44:16301-9
Abstract	BtuCD is an ATP binding cassette (ABC) transporter that facilitates uptake of vitamin B(12) into the cytoplasm of Escherichia coli. The crystal structures of BtuCD and its cognate periplasmic binding protein BtuF have been recently determined. We have now explored BtuCD-F function in vitro, both in proteoliposomes and in various detergents. BtuCD reconstituted into proteoliposomes has a significant basal ATP hydrolysis rate that is stimulated by addition of BtuF and inhibited by sodium ortho-vanadate. When using different detergents to solubilize BtuCD, the basal ATP hydrolysis rate, the ability of BtuF to stimulate hydrolysis, and the extent to which sodium ortho-vanadate inhibits ATP hydrolysis all vary significantly. Reconstituted BtuCD can mediate transport of vitamin B(12) against a concentration gradient when coupled to ATP hydrolysis by BtuD in the liposome lumen and BtuF outside the liposomes. These in vitro studies establish the functional competence of the BtuCD and BtuF preparations used in the crystallographic analyses for both ATPase and transport activities. Furthermore, the tight binding of BtuF to BtuCD under the conditions studied suggests that the binding protein may not dissociate from the transporter during the catalytic cycle, which may be relevant to the mechanisms of other ABC transporter systems.
Links	PubMed Online version:10.1021/bi0513103
Keywords	ATP-Binding Cassette Transporters/chemistry; ATP-Binding Cassette Transporters/genetics; ATP-Binding Cassette Transporters/metabolism; Adenosine Triphosphatases/metabolism; Biological Transport; Detergents/chemistry; Escherichia coli/metabolism; Escherichia coli Proteins/chemistry; Escherichia coli Proteins/genetics; Escherichia coli Proteins/metabolism; Liposomes; Models, Molecular; Periplasmic Binding Proteins/chemistry; Periplasmic Binding Proteins/genetics; Periplasmic Binding Proteins/metabolism; Protein Conformation; Vitamin B 12/metabolism
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