 |
|
Title
|
|
Crystal structure of a novel trimethoprim-resistant dihydrofolate reductase specified in Escherichia coli by R-plasmid R67.
|
|
|
Authors
|
|
D.A.Matthews,
S.L.Smith,
D.P.Baccanari,
J.J.Burchall,
S.J.Oatley,
J.Kraut.
|
|
|
Ref.
|
|
Biochemistry, 1986,
25,
4194-4204.
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
Crystalline R67 dihydrofolate reductase (DHFR) is a dimeric molecule with two
identical 78 amino acid subunits, each folded into a beta-barrel conformation.
The outer surfaces of the three longest beta strands in each protomer together
form a third beta barrel having six strands at the subunit interface. A unique
feature of the enzyme structure is that while the intersubunit beta barrel is
quite regular over most of its surface, an 8-A "gap" runs the full length of the
barrel, disrupting potential hydrogen bonds between beta-strand D in subunit I
and the adjacent corresponding strand of subunit II. It is proposed that this
deep groove is the NADPH binding site and that the association between protein
and cofactor is modulated by hydrogen-bonding interactions along one face of
this antiparallel beta-barrel structure. A hypothetical model is proposed for
the R67 DHFR-NADPH-folate ternary complex that is consistent with both the known
reaction stereoselectivity and the weak binding of 2,4-diamino inhibitors to the
plasmid-specified reductase. Geometrical comparison of this model with an
experimentally determined structure for chicken DHFR suggests that chromosomal
and type II R-plasmid specified enzymes may have independently evolved similar
catalytic machinery for substrate reduction.
|
|
|
|