Structural and functional insights into the rhizobial copper nitrite reductase from Bradyrhizobium japonicum USDA110

RAMÍREZ, CS; TOLMIE, C; OPPERMAN, DJ; BRONDINO, CD; FERRONI, FM

Rosario

Congreso; L Annual Meeting SAB; 2022

Sociedad Argentina de Biofísica

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 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 a resolution of 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, which transports two protons required by the stoichiometry of the reduction of nitrite to nitric oxide. We performed bioinformatic studies of cavities, surfaces and contact areas that are relevant for the biochemistry and function of the enzyme as well as on the physiological partner cytochrome c550 (BjCycA). We designed variants related to relevant structural features. We present here preliminary results about the effects of these variants on BjNirK activity.[1] Jaiswal S.K. et.al. (2021). Frontiers in Sustainable Food Systems. 4, 619676 [2] Delgado M.J. et.al. (2007). Chapter 6 - Denitrification in Rhizobia-Legume Symbiosis. In Biology of the Nitrogen Cycle. pp. 83-91, Elsevier, Amsterdam [3] Rose, S.L. et.al. (2022). Copper-Containing Nitrite Reductase. In Encyclopedia of Inorganic and Bioinorganic Chemistry, R.A. Scott (Ed.).