The sulfur shift: an activation mechanism for periplasmic nitrate reductase and formate dehydrogenase.
A structural rearrangement known as sulfur shift occurs in some Mo-containing enzymes of the DMSO reductase family. This mechanism is characterized by the displacement of a coordinating cysteine thiol (or SeCys in Fdh) from the first to the second shell of the Mo-coordination sphere metal. The hexa-coordinated Mo ion found in the as-isolated state cannot bind directly any exogenous ligand (substrate or inhibitors), while the penta-coordinated ion, attained upon sulfur shift, has a free binding site for direct coordination of the substrate. This rearrangement provides an efficient mechanism to keep a constant coordination number throughout an entire catalytic pathway. This mechanism is very similar to the carboxylate shift observed in Zn-dependent enzymes, and it has been recently detected by experimental means. In the present paper, we calculated the geometries and energies involved in the sulfur-shift mechanism using QM-methods (M06/(6-311++G(3df,2pd),SDD)//B3LYP/(6-31G(d),SDD)). The results indicated that the sulfur-shift mechanism provides an efficient way to enable the metal ion for substrate coordination.
REQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto , Rua do Campo Alegre s/n, 4169-007 Porto, Portugal.
Nuno M F S A
NM
Cerqueira
Pedro A
PA
Fernandes
Pablo J
PJ
Gonzalez
José J G
JJ
Moura
Maria J
MJ
Ramos
D003198:Computer Simulation; D005560:Formate Dehydrogenases / Q000737:chemistry*; D008958:Models, Molecular; D050901:Nitrate Reductase / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry*
D013455:Sulfur; D005560:Formate Dehydrogenases; D050901:Nitrate Reductase