Nitration at tyrosine 61 residue of Macrophomina phaseolina secretory glucanase brings a conformational change through a lock-unlock mechanism.

Abstract

Nitration of Tyrosine residue, is a footprint of its preceding nitrosative stress conditions that make nitric oxide-derived oxidants abundant. Such a post-translational chemical modification, as byproduct of a stressed condition, could be an onset of a functional pathway. Macrophomina phaseolina, which is a global devastating necrotrophic fungal pathogen, is hereby reported to have at least nine tyrosine nitrated proteins in its secretome; among them Glucanase is an important virulence secretory protein that gets nitrated at Y61. The immediate impact on the Glucanase is likely to be a perturbation on the protein itself, which would prepare the protein to function, i.e. structurally ready to recognize binding partners which could not get recognized otherwise. Y61 nitration stabilizes the enzyme's structure, particularly, its central channel within the enzyme's core. Its mechanical consequences operate at both local and global scales. The key driving factor is a positional switch of Y61 which is triggered by charge-charge repulsion between D63 and Y61 upon nitration. This switching is responsible for a critical 'lock-unlock' mechanism at the upper junction of the channel that regulates solvent exposure, underscoring Y61's pivotal role as a gating residue for the channel. While it's 'gating-in' at the junction unlocks and distorts the channel shape, its 'gating-out' locks the channel into a well-guarded conformation systematically regulating its overall exposure that can potentiate precise substrate routing towards the active site. The findings suggest that Y61 nitration-induced conformational changes have the potential to drive enzyme activation, representing a novel insight into the behavior of M. phaseolina glucanase.