1L9Q: Crystal Structure Of The I257l Variant Of The Copper- Containing Nitrite Reductase From Alcaligenes Faecalis S-6

Citation:
Abstract
Unlike the heme cd(1)-based nitrite reductase enzymes, the molecular mechanism of copper-containing nitrite reductases remains controversial. A key source of controversy is the productive binding mode of nitrite in the active site. To identify and characterize the molecular determinants associated with nitrite binding, we applied a combinatorial mutagenesis approach to generate a small library of six variants at position 257 in nitrite reductase from Alcaligenes faecalis S-6. The activities of these six variants span nearly two orders of magnitude with one variant, I257V, the only observed natural substitution for Ile257, showing greater activity than the native enzyme. High-resolution (> 1.8 A) nitrite-soaked crystal structures of these variants display different modes of nitrite binding that correlate well with the altered activities. These studies identify for the first time that the highly conserved Ile257 in the native enzyme is a key molecular determinant in directing a catalytically competent mode of nitrite binding in the active site. The O-coordinate bidentate binding mode of nitrite observed in native and mutant forms with high activity supports a catalytic model distinct from the heme cd(1) NiRs. (The atomic coordinates for I257V[NO(2)(-)], I257L[NO(2)(-)], I257A[NO(2)(-)], I257T[NO(2)(-)], I257M[NO(2)(-)] and I257G[NO(2)(-)] AfNiR have been deposited in the Protein Data Bank [PDB identification codes are listed in Table 2].)
PDB ID: 1L9QDownload
MMDB ID: 21697
PDB Deposition Date: 2002/3/26
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 1.7  Å
Source Organism:
Similar Structures:
Biological Unit for 1L9Q: trimeric; determined by author and by software (PISA)
Molecular Components in 1L9Q
Label Count Molecule
Proteins (3 molecules)
3
Copper-containing Nitrite Reductase
Molecule annotation
Chemicals (9 molecules)
1
6
2
3
* Click molecule labels to explore molecular sequence information.

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