1nqe
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OUTER MEMBRANE COBALAMIN TRANSPORTER (BTUB) FROM E. COLI
OverviewOverview
The outer membranes of Gram-negative bacteria possess transport proteins, essential for uptake of scarce nutrients. In TonB-dependent transporters, a conserved sequence of seven residues, the Ton box, faces the periplasm, and interacts with the inner membrane TonB protein to energize an active, transport cycle. A critical mechanistic step is the structural change in, the Ton box of the transporter upon substrate binding; this essential, transmembrane signaling event increases the affinity of the transporter, for TonB and enables active transport to proceed. We have solved crystal, structures of BtuB, the outer membrane cobalamin transporter from, Escherichia coli, in the absence and presence of cyanocobalamin (vitamin, B(12)). In these structures, the Ton box is ordered and undergoes a, conformational change in the presence of bound substrate. Calcium has been, implicated as a necessary factor for the high-affinity binding (K(d), approximately 0.3 nM) of cyanocobalamin to BtuB. We observe two bound, calcium ions that order three extracellular loops of BtuB, thus providing, a direct (and unusual) structural role for calcium.
About this StructureAbout this Structure
1NQE is a Single protein structure of sequence from Escherichia coli with MG and C8E as ligands. Full crystallographic information is available from OCA.
ReferenceReference
Substrate-induced transmembrane signaling in the cobalamin transporter BtuB., Chimento DP, Mohanty AK, Kadner RJ, Wiener MC, Nat Struct Biol. 2003 May;10(5):394-401. PMID:12652322
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