Unveiling the structural features of nonnative trimers of human superoxide dismutase 1

• Published in: Biochimica et biophysica acta. General subjects 2020-03, Vol.1864 (3), p.129483, Article 129483
• Main Authors: Chao, Wei-Chih, Lu, Jyh-Feng, Wang, Jinn-Shyan, Chiang, Tzu-Hsuan, Lin, Li-Ju, Lee, Yao-Lin, Chou, Pi-Tai
• Format: Article
• Language: English
• ISSN: 0304-4165; 1872-8006
• DOI: 10.1016/j.bbagen.2019.129483

Human SOD1 contains a single tryptophan residue (W32) which has been identified as a site of oxidative modification and a potentiator of aggregation involving in familial amyotrophic lateral sclerosis (fALS). In situ substitution of a tryptophan analog, 2,6-diazatryptophan ((2,6-aza)Trp) with its unique water-catalyzed proton transfer property, into proteins exhibits extraordinary sensitivity in the detection of subtle water-associated structural changes with only a few micro-molar concentration of samples. A combination of size-exclusion chromatography and water-catalyzed fluorescent emission was utilized to probe the structural features of metastable SOD1 nonnative trimers, the potential neurotoxic species in the fALS. The monomer of apo-A4V SOD1 exhibits variable conformations and the fastest trimeric formation rate compared to that of wild type and I113T. The trimeric A4V SOD1 exhibits the least water molecules surrounding the W32, while I113T and the wild type appear to have more water molecules in the proximity of W32. A small molecule stabilizer, 5-fluorouridine, effects the structural conformation of SOD1 nonnative trimers. Our studies unveil new insights into water-associated structural changes of SOD1 nonnative trimers and demonstrate that in situ incorporation of (2,6-aza)Trp is a sensitive and powerful tool for probing subtle changes of water environments during protein aggregation. The water-sensitive probe, (2,6-aza)Trp, demonstrates superior sensitivity for detecting modulation of water microsolvation, structural conformation during oligomer formation and 5FUrd binding to both wild type and mutant SOD1. [Display omitted] •A combination method was utilized to probe the structural features of metastable SOD1 nonnative trimers.•Subtle changes of water microenvironment around W32 are detected by the (2,6-aza)Trp with superior sensitivity.•The trimeric A4V SOD1 exhibits least water molecules around W32, followed by I113T, and the wild type.•A small molecules stabilizer, 5-fluorouridine,effects on both the formation and conformation of SOD1 nonnative trimers.