Crystal structure of C-terminal desundecapeptide nitrite reductase from Achromobacter cycloclastes

Abstract Monoclinic crystal structure of C-terminal desundecapeptide nitrite reductase (NiRc-11) from Achromobacter cycloclastes was determined at 2.6 A. NiRc-11 exists as a loose trimer in the crystal. Deletion of 11 residues eliminates all intersubunit hydrogen bonds mediated by the C-terminal tail. The rigid irregular coil 105–112, which constitutes part of the sidewall of the active site pocket, undergoes conformational changes and becomes highly flexible in NiRc-11. Correspondingly, the linker segments between the two copper sites 95–100 and 135–136 are partly relaxed in conformation, which leads to disrupted active site microenvironments responsible for the activity loss and spectral change of NiRc-11. Comparison with the native structure revealed a bulky residue Met331 fastened by hydrogen bonding, which may play a direct role in keeping the right copper site geometry by protruding its side chain against the irregular coil 105–112. Sequence alignment showed that the bulky residue is conserved at position 331, indicating an equal importance of C-terminal segment in other copper-containing nitrite reductases.