Binding mode of azide to ferric Aplysia limacina myoglobin. Crystallographic analysis at 1.9 A resolution.
The binding mode of azide to the ferric form of Aplysia limacina myoglobin has been studied by X-ray crystallography. The three-dimensional structure of the complex has been refined at 1.9 A resolution to a crystallographic R-factor of 13.9%, including 126 ordered solvent molecules. Azide binds to the heme iron, at the sixth co-ordination position, and is oriented towards the outer part of the distal site crevice. This orientation is stabilized by an ionic interaction with the side-chain of Arg66 (E10) which, from an outer orientation in the 'aquo-met' ligand-free myoglobin, folds back towards the distal site in the presence of the anionic ligand. In the absence of a hydrogen bond donor residue at the distal E7 position in Aplysia limacina myoglobin, a different polar residue, Arg66 at the E10 topological position, has been selected by molecular evolution in order to grant ligand stabilization.
Dipartimento di Genetica e Microbiologia, Università di Pavia, Italy.
A
A
Mattevi
G
G
Gatti
A
A
Coda
M
M
Rizzi
P
P
Ascenzi
M
M
Brunori
M
M
Bolognesi
D000818:Animals; D001048:Aplysia; D001386:Azides / Q000737:chemistry / Q000378:metabolism*; D005290:Ferric Compounds / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D009211:Myoglobin / Q000737:chemistry / Q000378:metabolism*; D014961:X-Ray Diffraction
D001386:Azides; D005290:Ferric Compounds; D009211:Myoglobin