15th August 2005
Daresbury Scientists Reveal Enzyme Mechanism
Understanding enzyme catalysis in the Nitrogen Cycle -
crystallography at atomic resolution on NWSGC MAD 10.1 at the SRS
The
nitrogen cycle is a process comparable to photosynthes is in biological
significance. Copper containing nitrite reductases are enzymes that perform
a crucial catalytic step in this cycle - the conversion on nitrite (NO 2 -)
to nitric oxide (NO). This reaction removes nitrogen from the soil and has
agronomic, environmental and medical impacts. We used 'crystal harvesting' and
substrate-soaking techniques to obtain crystal structures at atomic resolution
(0.9, 1.15 and 1.12 ũ of Achromobacter cycloclastes nitrite reductase in
its resting state, nitrite-bound and NO-bound forms. In addition, a structure at
1.1 Sresolution revealed the presence of both nitrite and NO at the catalytic
type 2 copper centres. The structure of the resting enzyme, measured on the
MAD 10.1 beamline, is the highest resolution reported for any copper protein.
These structures have provided insights into the process of nitrite reduction,
from the initial binding of substrate to the type 2 copper atom, its repositioning
prior to catalysis, bond breakage (O-NO) and the formation of a stable NO
adduct.
This work reports a collaboration between the Molecular Biophysics Group at Daresbury and the John Innes Centre, Norwich, and is published in the latest volume of the Proceedings of the National Academy of Sciences (USA) : Svetlana Antonyuk, Richard W. Strange, Gary Sawers, Robert R. Eady, S. Samar Hasnain, PNAS, 102 No. 34, 12041-12046, 2005.