Heterologous production and functional characterization of Bradyrhizobium japonicum copper-containing nitrite reductase and its physiological redox partner cytochrome c550

Abstract

Two domain copper-nitrite reductases (NirK) contain two types of copper centers, one electron transfer (ET) center of type 1 (T1) and a catalytic site of type 2 (T2). NirK activity...

Copper nitrite reductase from Sinorhizobium meliloti 2011: Crystal structure and interaction with the physiological versus a nonmetabolically related cupredoxin‐like mediator

“…In line with this observation, Sm NirK has a hydrophobic Val residue at this position and, as reported in our previous work, MV‐dependent activity of Sm NirK shows only 12% of the Ax NirK maximum turnover 22 . This correlation seems consistent as the same position is occupied by hydrophobic Leu residues in both Br 2D NirK 37 and Bj NirK, 17 which show less than 10% of the Ax NirK maximal activity 17,37 . A synchrotron radiation X‐ray (SRX) structure of Br 2D NirK (PDB ID: 6THF) showed an increased number of waters within the SC compared to our Sm NirK SRX structure, conserving the T2Cu‐coordinated water 37 .…”

“…Hydrophobic residues substituting Asn107 were also observed in the two‐domain rhizobial NirKs from Bradyrhizobium sp. ORS 375 ( Br 2D NirK) and B. japonicum USDA110 ( Bj NirK), both showing turnover numbers lower than those of Af NirK and Ac NirK 17,37 . In line with this observation, Sm NirK has a hydrophobic Val residue at this position and, as reported in our previous work, MV‐dependent activity of Sm NirK shows only 12% of the Ax NirK maximum turnover 22 .…”

“…We also evaluated the catalytic performance of Sm NirK using Sm Paz2 as mediator by chronoamperometry following a procedure reported for the Sm NirK‐ Sm Paz1 couple 17 . The results, analyzed with a Michaelis–Menten model, yielded i max = 3.79 ± 0.07 μA and K m app = 320 ± 20 μM nitrite, which indicates, in line with the solution kinetics, that Sm Paz2 can also act as a suitable in vitro ED to Sm NirK (Figure 3b).…”

“…NirKs receive electrons from physiological electron donors (EDs) such as small proteins like azurins, pseudoazurins, and cytochromes, which are genetically determined 5 . For example, Pseudomona chlororaphis ( Pc ) and Alcaligenes xyloxidants ( Ax ) NirKs receive electrons from an azurin, 13,14 S. meliloti ( Sm ) and Alcaligenes faecalis ( Af ) NirKs from pseudoazurins, 15,16 and Bradyrhizobium japonicum USDA110 ( Bj ) and Rhodobacter sphaeroides (Rs) NirKs from Type‐ c cytochromes 17,18 . All NirKs show a well‐conserved region above T1Cu that facilitates the interaction with external physiological EDs.…”

The effect of salinity stress on the Phaseolus vulgaris L. plant

“…The gradual increment of the soil EC amount may be related to the gradual high applied salt concentrations. However, a few studies have shown the adverse influence of salinity on pH and EC under different concentrations of salts (Cristaldi et al, 2020).…”