BPS2026 – The C. albicans virulence factor candidalysin switches polymerization mode in solution and in the membrane

Candida albicans invasion of human cells requires the candidalysin (CL) peptide. When CL is secreted in solution, it assembles into a basic oligomeric subunit that shows strong propensity to interact forming a linear polymer. Our data indicate that CL can assemble through two distinct polymerization mechanisms. In solution, CL primarily undergoes head-to-toe polymerization, where oligomeric units link end to end to form linear chains. As these chains elongate, their ends can meet and cyclize into a loop, which is thought to represent the insertion-competent structure for pore formation. By contrast, once associated with lipid bilayers, CL tends to reorganize through side-by-side polymerization, where oligomers instead interact laterally. We observed that lateral subunit interaction stabilizes the peptide within the membrane and supports the formation of more complex pore morphologies observed in atomic force microscopy studies. We proposed that head-to-toe assembly dominates in solution as a pre-insertion mechanism, whereas side-by-side packing emerges within the membrane to stabilize functional pores. To test this hypothesis, we created three CL variants with selectively altered terminal charges through N-terminal acetylation (ac-CL), C-terminal amidation (CL-am) or both modifications (ac-CL-am). Results in lipid membranes showed that ac-CL induced more membrane damage. However, the double modified variant ac-CL-am showed slower membrane disruption. On the other hand, mass photometry of CL in solution showed that the polymerization of the altered variants was slower than CL WT. Taken together, our findings indicate that CL polymerization is environmentally dependent: in solution it assembles via a head-to-toe arrangement, whereas in membranes it preferentially employs a side-by-side polymerization mechanism. Understanding of CL polymerization yields essential insights into CL self-assembly, pore formation, and membrane damage, establishing a basis for developing new antifungal therapeutics.