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PDBsum entry 2k0y
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Transport protein
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PDB id
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2k0y
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References listed in PDB file
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Key reference
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Title
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An acp structural switch: conformational differences between the apo and holo forms of the actinorhodin polyketide synthase acyl carrier protein.
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Authors
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S.E.Evans,
C.Williams,
C.J.Arthur,
S.G.Burston,
T.J.Simpson,
J.Crosby,
M.P.Crump.
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Ref.
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Chembiochem, 2008,
9,
2424-2432.
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PubMed id
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Abstract
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The actinorhodin (act) synthase acyl carrier protein (ACP) from Streptomyces
coelicolor plays a central role in polyketide biosynthesis. Polyketide
intermediates are bound to the free sulfhydryl group of a phosphopantetheine arm
that is covalently linked to a conserved serine residue in the holo form of the
ACP. The solution NMR structures of both the apo and holo forms of the ACP are
reported, which represents the first high resolution comparison of these two
forms of an ACP. Ensembles of twenty apo and holo structures were calculated and
yielded atomic root mean square deviations of well-ordered backbone atoms to the
average coordinates of 0.37 and 0.42 A, respectively. Three restraints defining
the protein to the phosphopantetheine interface were identified. Comparison of
the apo and holo forms revealed previously undetected conformational changes.
Helix III moved towards helix II (contraction of the ACP), and Leu43 on helix II
subtly switched from being solvent exposed to forming intramolecular
interactions with the newly added phosphopantetheine side chain. Tryptophan
fluorescence and S. coelicolor fatty acid synthase (FAS) holo-synthase (ACPS)
assays indicated that apo-ACP has a twofold higher affinity (K(d) of 1.1 muM)
than holo-ACP (K(d) of 2.1 muM) for ACPS. Site-directed mutagenesis of Leu43 and
Asp62 revealed that both mutations affect binding, but have differential affects
on modification by ACPS. Leu43 mutations in particular strongly modulate binding
affinity for ACPS. Comparison of apo- and holo-ACP structures with known models
of the Bacillus subtilis FAS ACP-holo-acyl carrier protein synthase (ACPS)
complex suggests that conformational modulation of helix II and III between apo-
and holo-ACP could play a role in dissociation of the ACP-ACPS complex.
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