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PDBsum entry 4n6b
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References listed in PDB file
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Key reference
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Title
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Structure of soybean serine acetyltransferase and formation of the cysteine regulatory complex as a molecular chaperone.
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Authors
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H.Yi,
S.Dey,
S.Kumaran,
S.G.Lee,
H.B.Krishnan,
J.M.Jez.
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Ref.
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J Biol Chem, 2013,
288,
36463-36472.
[DOI no: ]
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PubMed id
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Abstract
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Serine acetyltransferase (SAT) catalyzes the limiting reaction in plant and
microbial biosynthesis of cysteine. In addition to its enzymatic function, SAT
forms a macromolecular complex with O-acetylserine sulfhydrylase. Formation of
the cysteine regulatory complex (CRC) is a critical biochemical control feature
in plant sulfur metabolism. Here we present the 1.75-3.0 Å resolution x-ray
crystal structures of soybean (Glycine max) SAT (GmSAT) in apoenzyme,
serine-bound, and CoA-bound forms. The GmSAT-serine and GmSAT-CoA structures
provide new details on substrate interactions in the active site. The crystal
structures and analysis of site-directed mutants suggest that His(169) and
Asp(154) form a catalytic dyad for general base catalysis and that His(189) may
stabilize the oxyanion reaction intermediate. Glu(177) helps to position
Arg(203) and His(204) and the β1c-β2c loop for serine binding. A similar role
for ionic interactions formed by Lys(230) is required for CoA binding. The GmSAT
structures also identify Arg(253) as important for the enhanced catalytic
efficiency of SAT in the CRC and suggest that movement of the residue may
stabilize CoA binding in the macromolecular complex. Differences in the effect
of cold on GmSAT activity in the isolated enzyme versus the enzyme in the CRC
were also observed. A role for CRC formation as a molecular chaperone to
maintain SAT activity in response to an environmental stress is proposed for
this multienzyme complex in plants.
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