 |
|
Title
|
|
Structure of tropinone reductase-II complexed with NADP+ and pseudotropine at 1.9 A resolution: implication for stereospecific substrate binding and catalysis.
|
|
|
Authors
|
|
A.Yamashita,
H.Kato,
S.Wakatsuki,
T.Tomizaki,
T.Nakatsu,
K.Nakajima,
T.Hashimoto,
Y.Yamada,
J.Oda.
|
|
|
Ref.
|
|
Biochemistry, 1999,
38,
7630-7637.
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
Tropinone reductase-II (TR-II) catalyzes the NADPH-dependent reduction of the
carbonyl group of tropinone to a beta-hydroxyl group. The crystal structure of
TR-II complexed with NADP+ and pseudotropine (psi-tropine) has been determined
at 1.9 A resolution. A seven-residue peptide near the active site, disordered in
the unliganded structure, is fixed in the ternary complex by participation of
the cofactor and substrate binding. The psi-tropine molecule is bound in an
orientation which satisfies the product configuration and the stereochemical
arrangement toward the cofactor. The substrate binding site displays a
complementarity to the bound substrate (psi-tropine) in its correct orientation.
In addition, electrostatic interactions between the substrate and Glu156 seem to
specify the binding position and orientation of the substrate. A comparison
between the active sites in TR-II and TR-I shows that they provide different van
der Waals surfaces and electrostatic features. These differences likely
contribute to the correct binding mode of the substrates, which are in opposite
orientations in TR-II and TR-I, and to different reaction stereospecificities.
The active site structure in the TR-II ternary complex also suggests that the
arrangement of the substrate, cofactor, and catalytic residues is
stereoelectronically favorable for the reaction.
|
|
|
|