Effects of His mutations on the fibrillation of amyloidogenic Vλ6 protein Wil under acidic and physiological conditions

Recently, we showed that the recombinant (r) Vλ6 protein Wil exhibits a more disrupted residual structure and a longer lag time for fibril formation than the rVλ6 protein Jto under highly unfolding conditions at pH 2. Here, we focused on the roles of three histidine residues specific for Wil, which are positively charged at pH 2 and could repel one another. Heteronuclear relaxation experiments revealed that a mutant Wil with H34Q, H53Q and H93S mutations (3HmutWil) had larger R₂ values only in the region of residues 22-55 and formed fibrils much earlier than Wil at pH 2. 3HmutWil also showed a decrease in ThT fluorescence intensity compared with Wil in fibrillation experiments at pH 7.5. The present results suggest that these three histidine residues play important roles in the fibrillation of Wil at both pH 2 and pH 7.5.