7.6.2.8 evolution ECF-transporters are multi-subunit membrane complexes that consist of two ATPases, similar to the ATPases of ABC transporters, and two membrane embedded proteins, not related to any other protein family -, 750412 7.6.2.8 evolution Escherichia coli vitamin B12 transporter BtuCD-F is a type II importer and belongs to the ATP-binding cassette (ABC) transporter superfamily 751661 7.6.2.8 evolution the enzyme is a ABC transporter, all ABC-type ATPases encoded by the organism are predicted to be part of classical ABC transporters, and not ECF transporters. The organism does not encode an ECF-module. BtuM homologues (apart from one exception) are found exclusively in organisms lacking an ECF-module. But BtuMTd structurally resembles the S-components of ECF transporters 751670 7.6.2.8 malfunction ABCD4 dysfunction results in a failure of lysosomal vitamin B12 release 749821 7.6.2.8 malfunction gene disruption eliminates the ability of Mycobacterium tuberculosis to use exogenous vitamin B12 in vitro 734820 7.6.2.8 malfunction mutations in ABCD4 result in a failure to release vitamin B12 from lysosomes. A similar phenotype is caused by mutations in gene LMBRD1, which encodes the lysosomal membrane protein LMBD1. ABCD4 lysosomal localization is disturbed by knockout of LMBRD. Mutation of ABCD4, which is known as the cblJ complementation group, results in the failure of the release of cobalamin from lysosomes. A similar phenotype in patients within the cblF group is caused by mutations of LMBD1, a lysosomal membrane protein. Mistargeting of mutant LMBD1 affects the distribution of ABCD4. Thus, mutations of ABCD4 and LMBD1 result in a quite similar phenotype. A putative region of ABCD4 that interacts with LMBD1 might be masked by the exchange of the regions around transmembrane domains (TMs) 2 and 5 752200 7.6.2.8 malfunction substitution of W66 in BtuF with tyrosine or leucine reduced the affinity 3fold compared to wild-type, and a change to histidine or arginine reduces it more than 10fold 752221 7.6.2.8 additional information ABC importers follow the two-site access model3, in which ATP binding and hydrolysis switch the accessibility of the transmembrane domain for the substrate from an inward facing (accessible from the cytoplasm) to an outward-facing (accessible from the extracellular site) conformation, conformational changes by single-molecule FRET measurements combined with molecular dynamics simulations, two different transport cycles are analyzed 751644 7.6.2.8 additional information conformational coupling, molecular dynamics simulations using BtuCD-F is embedded in a solvated phosphatidylcholine bilayer, configurational entropy, pairwise residue-residue forces in BtuCD-F are analyzed through force distribution analysis, overview 750063 7.6.2.8 additional information function and structure of BtuMTd, cobalamin binding structure, overview 751670