A distant angiogenin variant causes amyotrophic lateral sclerosis through loss-of-function mechanisms: Insights from long-timescale atomistic simulations and conformational dynamics.

Amyotrophic Lateral Sclerosis (ALS) is a progressive and incurable neurodegenerative disorder characterized by the degeneration of motor neurons leading to severe muscle atrophy, respiratory failure and death within 3-5 years of disease onset. Missense mutations in Angiogenin (ANG) cause ALS through loss of either ribonucleolytic activity or nuclear translocation activity or both of these functions. Although loss-of-function mechanisms of several rare and ALS-causing ANG variants have been studied before, the structure-function relationship and subsequent functional loss mechanisms of certain novel and uncharacterized rare variants have not been deciphered hitherto. In this study, the structural and dynamic properties of the distantly-located I71V variant, on the functional sites of ANG have been investigated to understand its role in ALS etiology and progression. The I71V variant has a minor allele frequency of <0.06% and thus is classified as a rare variant. Our extensive in silico investigation comprising 1-μs molecular dynamics (MD) simulations, conformational dynamics and related integrated analyses reveal that the I71V variant induces a characteristic conformational switching of catalytic His114 residue resulting in loss of ribonucleolytic activity. Molecular docking and a residue-residue interaction network propagated by an allosteric pathway further support these findings. Moreover, while no conformational alteration of nuclear localization signal governing the nuclear translocation activity was observed, an escalation in mutant plasticity was detected in the structural and essential dynamics simulations. Overall, our study emphasizes that the structure-function relationship of frequently mutating novel ANG variants needs to be established and prioritized in order to advance the pathophysiology and therapeutics of ALS.