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Title
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Crystal structure of the pyridoxal-5'-phosphate dependent cystathionine beta-lyase from Escherichia coli at 1.83 A.
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Authors
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T.Clausen,
R.Huber,
B.Laber,
H.D.Pohlenz,
A.Messerschmidt.
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Ref.
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J Mol Biol, 1996,
262,
202-224.
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PubMed id
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Abstract
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Cystathionine beta-lyase (CBL) is a member of the gamma-family of PLP-dependent
enzymes, that cleaves C beta-S bonds of a broad variety of substrates. The
crystal structure of CBL from E. coli has been solved using MIR phases in
combination with density modification. The structure has been refined to an
R-factor of 15.2% at 1.83 A resolution using synchroton radiation diffraction
data. The asymmetric unit of the crystal cell (space group C222(1)) contains two
monomers related by 2-fold symmetry. A homotetramer with 222 symmetry is built
up by crystallographic and non-crystallographic symmetry. Each monomer of CBL
can be described in terms of three spatially and functionally different domains.
The N-terminal domain (residues 1 to 60) consists of three alpha-helices and one
beta-strand. It contributes to tetramer formation and is part of the active site
of the adjacent subunit. The second domain (residues 61 to 256) harbors PLP and
has an alpha/beta-structure with a seven-stranded beta-sheet as the central
part. The remaining C-terminal domain (residues 257 to 395), connected by a long
alpha-helix to the PLP-binding domain, consists of four helices packed on the
solvent-accessible side of an antiparallel four-stranded beta-sheet. The fold of
the C-terminal and the PLP-binding domain and the location of the active site
are similar to aminotransferases. Most of the residues in the active site are
strongly conserved among the enzymes of the transsulfuration pathway.
Additionally, CBL is homologous to the mal gamma gene product indicating an
evolutionary relationship between alpha and gamma-family of PLP-dependent
enzymes. The structure of the beta, beta, beta-trifluoroalanine inactivated CBL
has been refined at 2.3 A resolution to an R-factor of 16.2%. It suggests that
Lys210, the PLP-binding residue, mediates the proton transfer between C alpha
and S gamma.
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