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PDBsum entry 1m5h
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Crystal structures and enzymatic properties of three formyltransferases from archaea: environmental adaptation and evolutionary relationship.
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Authors
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B.Mamat,
A.Roth,
C.Grimm,
U.Ermler,
C.Tziatzios,
D.Schubert,
R.K.Thauer,
S.Shima.
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Ref.
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Protein Sci, 2002,
11,
2168-2178.
[DOI no: ]
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PubMed id
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Abstract
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Formyltransferase catalyzes the reversible formation of formylmethanofuran from
N(5)-formyltetrahydromethanopterin and methanofuran, a reaction involved in the
C1 metabolism of methanogenic and sulfate-reducing archaea. The crystal
structure of the homotetrameric enzyme from Methanopyrus kandleri (growth
temperature optimum 98 degrees C) has recently been solved at 1.65 A resolution.
We report here the crystal structures of the formyltransferase from
Methanosarcina barkeri (growth temperature optimum 37 degrees C) and from
Archaeoglobus fulgidus (growth temperature optimum 83 degrees C) at 1.9 A and
2.0 A resolution, respectively. Comparison of the structures of the three
enzymes revealed very similar folds. The most striking difference found was the
negative surface charge, which was -32 for the M. kandleri enzyme, only -8 for
the M. barkeri enzyme, and -11 for the A. fulgidus enzyme. The hydrophobic
surface fraction was 50% for the M. kandleri enzyme, 56% for the M. barkeri
enzyme, and 57% for the A. fulgidus enzyme. These differences most likely
reflect the adaptation of the enzyme to different cytoplasmic concentrations of
potassium cyclic 2,3-diphosphoglycerate, which are very high in M. kandleri (>1
M) and relatively low in M. barkeri and A. fulgidus. Formyltransferase is in a
monomer/dimer/tetramer equilibrium that is dependent on the salt concentration.
Only the dimers and tetramers are active, and only the tetramers are
thermostable. The enzyme from M. kandleri is a tetramer, which is active and
thermostable only at high concentrations of potassium phosphate (>1 M) or
potassium cyclic 2,3-diphosphoglycerate. Conversely, the enzyme from M. barkeri
and A. fulgidus already showed these properties, activity and stability, at much
lower concentrations of these strong salting-out salts.
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Figure 5.
Fig. 5. Structure of the formyltransferase. (A) The
tetramer presented as a Ribbon diagram indicates a particularly
extended contact region between subunits 1 (red) and 2 (green)
and the equivalent subunits 3 (blue) and 4 (orange). (B) The
Ribbon diagram of the monomer visualizes the location of the
insertion region (blue), the meander region (black circle), and
the loop between strands 6 and 7 (black arrow). (C) The stereo
C[  ]-plot of the
superimposed monomers of the enzymes from M. barkeri (red), A.
fulgidus (yellow), and M. kandleri (green) documents their
similar fold, in particular, in the core regions of the two
lobes. This figure was generated using the program MOLSCRIPT
(Kraulis 1991).
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Figure 6.
Fig. 6. The electrostatic properties of the
formyltransferase tetramer from (A) M. barkeri, (B) A. fulgidus,
and (C) M. kandleri. The molecule surface is coated according to
the electrostatic potential: The extreme ranges of red and blue
represent potentials of -20k[B]T and 20k[B]T, respectively
(where k[B] is the Boltzmann constant and T is temperature). The
electrostatic surface potential of the enzymes from M. barkeri
and A. fulgidus is nearly neutral, and that of the M. kandleri
enzyme highly negative, reflecting the dominance of acidic to
basic residues. The potentials are calculated under salt-free
conditions. The figure was generated using the program GRASP
(Nicholls et al. 1993).
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The above figures are
reprinted
by permission from the Protein Society:
Protein Sci
(2002,
11,
2168-2178)
copyright 2002.
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