View source for 1nqh

[[Image:1nqh.gif|left|200px]]<br /><applet load="1nqh" size="450" color="white" frame="true" align="right" spinBox="true" 
caption="1nqh, resolution 3.10&Aring;" />
'''OUTER MEMBRANE COBALAMIN TRANSPORTER (BTUB) FROM E. COLI, WITH BOUND CALCIUM AND CYANOCOBALAMIN (VITAMIN B12) SUBSTRATE'''<br />

==Overview==
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 Structure==
1NQH is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with CA, CNC and C8E as [http://en.wikipedia.org/wiki/ligands ligands]. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1NQH OCA]. 

==Reference==
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:[http://ispc.weizmann.ac.il//pmbin/getpm?pmid=12652322 12652322]
[[Category: Escherichia coli]]
[[Category: Single protein]]
[[Category: Chimento, D.P.]]
[[Category: Kadner, R.J.]]
[[Category: Mohanty, A.K.]]
[[Category: Wiener, M.C.]]
[[Category: C8E]]
[[Category: CA]]
[[Category: CNC]]
[[Category: beta barrel]]
[[Category: calcium binding]]
[[Category: cobalamin]]
[[Category: membrane transport]]
[[Category: vitamin b12]]

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