Unveiling Cell Wall Structure and Echinocandin Response in Candida auris and Candida albicans via Solid-State NMR

Invasive candidiasis affects 1.6 million people annually, implicating high mortality and morbidity in immunocompromised and hospitalized patients. Echinocandins, inhibitors of {beta}-1,3-glucan synthesis, are used as a first-line treatment; however, their efficacy is increasingly compromised by resistance and tolerance. To understand how echinocandins remodel Candida cell wall structures, thereby reducing drug effectiveness, this study compares the effects of echinocandin exposure on the cell walls of the prevalent pathogen Candida albicans and the recently emerged multidrug-resistant superbug Candida auris. High-resolution solid-state NMR analysis revealed a conserved cell wall structure in both species, with a rigid inner layer composed of closely associated chitin microfibrils and {beta}-1,3-glucans, supported by a flexible network of {beta}-1,6-glucans and additional {beta}-1,3-glucans. Despite the presence of N-mannan fibrils in the outer layer, mannan components are mobile and rely on -1,2-linked mannoside sidechains to maintain contact with chitin and {beta}-1,3-glucans. Caspofungin treatment rigidifies certain mannan sidechains and {beta}-1, 6-glucans to reinforce the cell wall in response to the depletion of most {beta}-1,3-glucans. While caspofungin treatment reduced water permeability in both species, only C. albicans responded by inducing cell wall thickening and changes in chitin and {beta}-1,3-glucan dynamics. Furthermore, the deletion of KRE6 genes encoding {beta}-1,6-glucan synthase reduced the echinocandin susceptibility of C. auris, and the impaired {beta}-1,6-glucan biosynthesis were offset by compensatory upregulation of this wall component due to caspofungin treatment. The profound alterations induced by caspofungin in Candida cell wall architecture suggest that cell wall structural contribute substantially to drug resistance and tolerance.