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PDBsum entry 2vmp
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References listed in PDB file
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Key reference
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Title
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Structural and functional studies of bacillus stearothermophilus serine hydroxymethyltransferase: the role of asn(341), Tyr(60) and phe(351) in tetrahydrofolate binding.
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Authors
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V.R.Pai,
V.Rajaram,
S.Bisht,
B.S.Bhavani,
N.A.Rao,
M.R.Murthy,
H.S.Savithri.
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Ref.
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Biochem J, 2009,
418,
635-642.
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PubMed id
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Abstract
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SHMT (serine hydoxymethyltransferase), a type I pyridoxal 5'-phosphate-dependent
enzyme, catalyses the conversion of L-serine and THF (tetrahydrofolate) into
glycine and 5,10-methylene THF. SHMT also catalyses several THF-independent side
reactions such as cleavage of beta-hydroxy amino acids, transamination,
racemization and decarboxylation. In the present study, the residues Asn(341),
Tyr(60) and Phe(351), which are likely to influence THF binding, were mutated to
alanine, alanine and glycine respectively, to elucidate the role of these
residues in THF-dependent and -independent reactions catalysed by SHMT. The
N341A and Y60A bsSHMT (Bacillus stearothermophilus SHMT) mutants were inactive
for the THF-dependent activity, while the mutations had no effect on
THF-independent activity. However, mutation of Phe(351) to glycine did not have
any effect on either of the activities. The crystal structures of the glycine
binary complexes of the mutants showed that N341A bsSHMT forms an external
aldimine as in bsSHMT, whereas Y60A and F351G bsSHMTs exist as a mixture of
internal/external aldimine and gem-diamine forms. Crystal structures of all of
the three mutants obtained in the presence of L-allo-threonine were similar to
the respective glycine binary complexes. The structure of the ternary complex of
F351G bsSHMT with glycine and FTHF (5-formyl THF) showed that the monoglutamate
side chain of FTHF is ordered in both the subunits of the asymmetric unit,
unlike in the wild-type bsSHMT. The present studies demonstrate that the
residues Asn(341) and Tyr(60) are pivotal for the binding of THF/FTHF, whereas
Phe(351) is responsible for the asymmetric binding of FTHF in the two subunits
of the dimer.
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