Mechanistic insights into the host cell damage mechanism of Candida albicans virulence factor candidalysin

Candida albicans is a commensal fungus that can causes epithelial infections and life-threatening invasive candidiasis. The fungus secretes candidalysin (CL), a peptide that causes host cell damage and immune activation by permeation of epithelial membranes. The mechanism of CL action involves strong peptide assembly into polymers in solution. The ends of linear CL polymers can join, forming loops that become pores upon binding to membranes. CL polymers constitute a therapeutic target for candidiasis, but little is known about mechanistic details of CL self-assembly. We have examined the assembly mechanism of CL using biophysical tools, including atomic force microscopy. This single-molecule method revealed that CL polymerization involves a convolution of four processes. Self-assembly begins with the formation of a basic CL subunit that acts as the polymer seed. CL polymerization proceeds via addition of subunits, and as polymers grow they can curve and form loops. Additionally, secondary polymerization can occur and cause branching. Interplay between the different rates of these reactions determines the distribution of CL particle types, indicating a kinetic control mechanism. This presentation will summarize recent work in this direction which was recently published [J Biol Chem 300, 107370 (2024); PMID: 38750794]. We will also discuss ongoing work focused on identifying the role the CL termini play in the polymerization reaction(s) and subsequent membrane damage. Taken together this work elucidates key physical attributes underlying CL self-assembly and evokes potential pharmaceutical development.