Mechanistic Characterization of NABi as a Selective Inhibitor of SOD1G93A Aggregation: Structural Basis and Therapeutic Implications for ALS

Abstract

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by the progressive loss of motor neurons, with familial ALS (fALS) frequently caused by mutations in Cu/Zn superoxide dismutase (SOD1). The G93A mutation, one of the most aggressive forms, promotes the formation of cytotoxic protein aggregates through cross-β-sheet structures, leading to neuronal dysfunction and death. In this study, we investigated the therapeutic potential of NABi (natural Aβ binder and Aβ-aggregation inhibitor), a stable small engineered protein composed of the N-terminal 90 amino acids of SOD1, originally developed to target amyloid-β aggregation in Alzheimer’s disease. Given the shared β-sheet-rich aggregation mechanisms between amyloid-β and mutant SOD1 proteins, we hypothesized that NABi could serve as a dual-action therapeutic for both diseases. Through an integrated approach involving structural, biochemical, and cellular analyses, we demonstrate that NABi exhibits a 4-fold greater binding affinity for SOD1G93A compared to SOD1WT, selectively targeting the mutant protein via specific hydrophobic interactions. Structural modeling using AlphaFold2 reveals that the G93A mutation exposes hydrophobic residues that create an optimal binding interface for NABi. Functionally, NABi effectively inhibits SOD1G93A aggregation, as demonstrated by filter trap assays and immunofluorescence microscopy, while maintaining the protein in a soluble, nontoxic state. Importantly, coexpression of NABi reduces SOD1G93A-induced cytotoxicity by approximately 4-fold, significantly enhancing neuronal survival. These findings establish NABi as a promising therapeutic candidate for SOD1G93A-associated familial ALS, demonstrating its capacity to selectively target pathological protein conformations while preserving normal cellular function. Our results support the development of NABi as an innovative pan-therapeutic approach targeting shared aggregation pathways across multiple neurodegenerative diseases.