THE RHIZOBIAL COPPER NITRITE REDUCTASE FROM BRADYRHIZOBIUM JAPONICUM USDA110: STRUCTURE AND BIOPHYSICS

RAMIREZ, C.S.; TOLMIE, C; OPPERMAN, D.J.; RIVAS, M.G.; GONZALEZ, PABLO; BRONDINO, C.D.; FERRONI, F.M.

Mar del Plata

Congreso; XVIII Reunión Anual de la Asociación Argentina de Cristalografía; 2023

Asociación Argentina de Cristalografía (AACr)/INTEMA (CONICET)/UNiversidad del mar del Plata

Denitrification plays a key role in soil and nitrogen metabolism in Rhizobacteria used as bioinoculants [1]. The regulation of the number of endosymbiont-Bradyrhizobium nodules in the roots of soya plants is determined in part by the nitrite reductase activity [2]. We report here the crystal structure of the copper-containing nitrite reductase from the Gram-negative bacterium B. japonicum USDA110 (BjNirK) solved at 1.3 Å. It showed a striking resemblance with the overall structure of the well-known class I NirKs composed of two Greek key β-barrel domains [3]. The enzyme had lower activity than the class I NirKs, which can likely be ascribed to structural differences in the secondary proton channel (SPC), which transports two protons required by the stoichiometry of nitrite reduction to nitric oxide. We performed biophysics studies (EPR, UV-vis spectroscopy, and Resonance RAMAN) and bioinformatics to complement the structural data. We analyze the interaction with the physiological electron donor cytochrome c550 (BjCycA), the proton channels, and the main functional features (T1Cu and T2CU centers).