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Title
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A novel calcium binding site in the galactose-binding protein of bacterial transport and chemotaxis.
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Authors
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N.K.Vyas,
M.N.Vyas,
F.A.Quiocho.
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Ref.
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Nature, 1987,
327,
635-638.
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PubMed id
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Abstract
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The refined 1.9-A resolution structure of the periplasmic D-galactose-binding
protein (GBP) reveals a calcium ion surrounded by seven ligands, all protein
oxygen atoms. A nine-residue loop (amino-acid positions 134-142), which is
preceded by a beta-turn and followed by a beta-strand, provides five ligands
from every second residue. The last two ligands are supplied by the carboxylate
group of Glu 205. The entire GBP Ca2+-binding site adopts a conformation very
similar to the site in the 'helix-loop-helix' or 'EF-hand' unit commonly found
in intracellular calcium-binding proteins, but without the two helices.
Structural analyses have also uncovered the sugar-binding site some 30 A from
the calcium and a site for interacting with the membrane-bound trg chemotactic
signal transducer approximately 45 A from the calcium. Our results show that a
common tight calcium binding site of ancient origin can be tethered to different
secondary structures. They also provide the first demonstration of a
metal-binding site in a protein which is involved in bacterial active transport
and chemotaxis.
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