Structure and Conservation of Amyloid Spines From the Candida albicans Als5 Adhesin.

Abstract

Candida Als family adhesins mediate adhesion to biological and abiotic substrates, as well as fungal cell aggregation, fungal-bacterial co-aggregation and biofilm formation. The activity of at least two family members, Als5 and Als1, is dependent on amyloid-like protein aggregation that is initiated by shear force. Each Als adhesin has a ∼300-residue N-terminal Ig-like/invasin region. The following 108-residue, low complexity, threonine-rich (T) domain unfolds under shear force to expose a critical amyloid-forming segment 322SNGIVIVATTRTV334 at the interface between the Ig-like/invasin domain 2 and the T domain of Candida albicans Als5. Amyloid prediction programs identified six potential amyloidogenic sequences in the Ig-like/invasin region and three others in the T domain of C. albicans Als5. Peptides derived from four of these sequences formed fibrils that bound thioflavin T, the amyloid indicator dye, and three of these revealed atomic-resolution structures of cross-β spines. These are the first atomic-level structures for fungal adhesins. One of these segments, from the T domain, revealed kinked β-sheets, similarly to LARKS (Low-complexity, Amyloid-like, Reversible, Kinked segments) found in human functional amyloids. Based on the cross-β structures in Als proteins, we use evolutionary arguments to identify functional amyloidogenic sequences in other fungal adhesins, including adhesins from Candida auris. Thus, cross-β structures are often involved in fungal pathogenesis and potentially in antifungal therapy.