K114 (trans, trans)-bromo-2,5-bis(4-hydroxystyryl)benzene is an efficient detector of cationic amyloid fibrils

Cationic amyloid fibrils found in human semen enhance the transmission of the human immunodeficiency virus (HIV) and thus, are named semen-derived enhancer of virus infection (SEVI). The mechanism for the enhancement of transmission is not completely understood but it has been proposed that SEVI neutralizes the repulsion that exists between the negatively charged viral envelope and host cell membrane. Consistent with this view, here we show that the fluorescence of cationic thioflavin T (ThT) in the presence of SEVI is weak, and thus ThT is not an efficient detector of SEVI. On the other hand, K114 ((trans, trans)-bromo-2,5-bis(4-hydroxystyryl)benzene) forms a highly fluorescent, phenolate-like species on the cationic surface of SEVI. This species does not form in the presence of amyloid fibrils from insulin and amyloid-β protein, both of which are efficiently detected by ThT fluorescence. Together, our results show that K114 is an efficient detector of SEVI.