Asymmetric states of vitamin B₁₂ transporter BtuCD are not discriminated by its cognate substrate binding protein BtuF.

BtuCD is an ABC transporter catalyzing the uptake of vitamin B₁₂ across the Escherichia coli inner membrane. A previously reported X-ray structure of BtuCD in complex with the periplasmic vitamin B₁₂-binding protein BtuF revealed asymmetry of the transmembrane BtuC subunits. The functional relevance of this asymmetry has remained uncertain.

In vitro folding and assembly of the Escherichia coli ATP-binding cassette transporter, BtuCD.

Studies on membrane protein folding have focused on monomeric α-helical proteins and a major challenge is to extend this work to larger oligomeric membrane proteins. Here, we study the Escherichia coli (E. coli) ATP-binding cassette (ABC) transporter that imports vitamin B(12) (the BtuCD protein) and use it as a model system for investigating the folding and assembly of a tetrameric membrane protein complex.

Asymmetry in the structure of the ABC transporter-binding protein complex BtuCD-BtuF.

BtuCD is an adenosine triphosphate-binding cassette (ABC) transporter that translocates vitamin B12 from the periplasmic binding protein BtuF into the cytoplasm of Escherichia coli. The 2.6 angstrom crystal structure of a complex BtuCD-F reveals substantial conformational changes as compared with the previously reported structures of BtuCD and BtuF.

Transport capabilities of eleven gram-positive bacteria: comparative genomic analyses.

The genomes of eleven Gram-positive bacteria that are important for human health and the food industry, nine low G+C lactic acid bacteria and two high G+C Gram-positive organisms, were analyzed for their complement of genes encoding transport proteins. Thirteen to 18% of their genes encode transport proteins, larger percentages than observed for most other bacteria. All of these bacteria possess channel proteins, some of which probably function to relieve osmotic stress.

In vitro functional characterization of BtuCD-F, the Escherichia coli ABC transporter for vitamin B12 uptake.

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.

The tripartite tricarboxylate transporter (TTT) family.

Extracytoplasmic solute binding receptors are constituents of primary and secondary active transport systems. Previous studies have shown that the constituents of two such families (ABC and TRAP-T) occur in bacteria and archaea and have undergone minimal shuffling of constituents between systems during evolutionary history. We here show that a third family of binding receptor-dependent transporters, the tripartite tricarboxylate transporter (TTT) family, the prototype of which is the TctABC system of Salmonella typhimurium, occurs in many bacteria but not in archaea or eukaryotes.

An automated program to screen databases for members of protein families.

We have developed a program, ScreenTransporter (ST), to screen for potential members of recognized transporter families. This program uses Blastpgp as the engine to search a nonredundant database, NRDB90, based on an adjustable E-value cut-off as well as adjustable protein size criteria. Additional parameters can be integrated in later versions.

Web-based programs for the display and analysis of transmembrane alpha-helices in aligned protein sequences.

We developed novel programs for displaying and analyzing the transmembrane alpha-helical segments (TMSs) in the aligned sequences of homologous integral membrane proteins. TMS_ALIGN predicts the positions of putative TMSs in multiply aligned protein sequences and graphically shows the TMSs in the alignment. TMS_SPLIT (1).

The multidrug/oligosaccharidyl-lipid/polysaccharide (MOP) exporter superfamily.

The multidrug/oligosaccharidyl-lipid/polysaccharide (MOP) exporter superfamily (TC #2.A.66) consists of four previously recognized families: (a) the ubiquitous multi-drug and toxin extrusion (MATE) family; (b) the prokaryotic polysaccharide transporter (PST) family; (c) the eukaryotic oligosaccharidyl-lipid flippase (OLF) family and (d) the bacterial mouse virulence factor family (MVF).