Cupredoxin domain 1 of Copper-containing nitrite reductase and two-domain laccase
Copper-containing nitrite reductase (CuNIR), which catalyzes the reduction of NO2- to NO, is the key enzyme in the denitrification process in denitrifying bacteria. CuNIR contains at least one type 1 copper center and a type 2 copper center, which serves as the active site of the enzyme. A histidine, bound to the Type 2 Cu center, is responsible for binding and reducing nitrite. A Cys-His bridge plays an important role in facilitating rapid electron transfer from the type 1 center to the type 2 center. A reduced type I blue copper protein (pseudoazurin) was found to be a specific electron transfer donor for the copper-containing NIR in bacteria Alcaligenes faecalis. The two-domain laccase (small laccase) in this family differs significantly from all laccases. It resembles two domain nitrite reductase in both sequence homology and structure similarity. It consists of two domains and forms trimers and hence resembles the quaternary structure of nitrite reductases more than that of larger laccases.
Jiyao W et al.(2023). "The conserved domain database in 2023.",