Cell wall changes and proteome remodelling induced by Sida hermaphrodita seed extract in Candida albicans

Abstract Candida albicans is the leading etiological agent of both superficial and systemic candidiasis. Difficulties in the treatment of fungal infections result from the limited efficacy and high toxicity of the most commonly used antibiotics. The aim of this study was to analyse the effect of a protein extract from Sida hermaphrodita (Virginia mallow) seeds on cells of the clinical wild-type strain of C. albicans and to identify the cellular targets of this effect. Light microscopy, scanning electron microscopy, flow cytometry, infrared spectroscopy (FTIR), and LC–MS/MS Quantitative SWATH-MS were used to perform detailed analysis of changes occurring in cells after incubation with the seed extract at various concentrations (0.76–100 µg mL − 1 ). It was demonstrated that the extract at all concentrations significantly limited the growth of C. albicans cells and reduced their viability, causing cell death via necrosis (MIC 50 was 25 µg mL − 1 ). After treatment with the extract, the cells were characterised by more intense and uneven fluorescence of individual cell wall layers: chitin and β-1,3-glucan. The SEM analysis revealed deformations in the cell shape and cells with numerous post-division scars located across the entire surface or at one of the poles. The flow cytometric analysis of the cell wall showed that the seed extract caused exposure of the β-1,3-glucan and chitin layers in the fungal cells, with a simultaneous reduction in mannans. These observations were confirmed by FTIR analyses, which revealed a decrease in the intensity of signals characteristic for cell wall polysaccharides, mannans, in the extract-treated cells. The AFM analysis showed changes in the nanomechanical properties of cells after treatment with extract at the highest concentration, i.e. an increase in elasticity, compared to control cells. The proteomic analyses revealed that the seed extract caused metabolic flexibility, reflected by the upregulation of mitochondrial and energy-associated proteins and the repression of ribosome-associated and biosynthetic proteins. Raman analysis provided information on the content of secondary protein structures in the extract. Immunoblotting using antibodies directed against lipid transfer protein and vicilins revealed proteins with molecular mass of 17, 63 kDa and 30, 35, 48, and 60 kDa, respectively. The extract is a promising material for the development of a new antifungal preparation with activity against C. albicans .