Sap6,a secreted aspartyl proteinase,participates in maintenance the cell surface integrity of Candida albicans

Background: the polymorphic species candida albicans is the major cause of candidiasis in humans. the secreted aspartyl proteinases (saps) of c. albicans,encoded by a family of 10 sap genes,have been investigated as the virulent factors during candidiasis. however,the biological functions of most sap proteins are still uncertain. in this study,we applied co-culture system of c. albicans and thp-1 human monocytes to explore the pathogenic roles and biological functions of sap proteinases. results: after 1 hr of co-culture of c. albicans strains and thp-1 human monocytes at 37°c,more than 60% of the thp-1-engulfed wild type and δsap5 candida cells were developing long hyphae. however,about 50% of thp-1-engulfed δsap6 candida cells were generating short hyphae,and more dead candida cells were found in δsap6 strain that was ingested by thp-1 cells (about 15% in δsap6 strain vs. 2 ∼ 2.5% in sc5314 and δsap5 strains). the immunofluorescence staining demonstrated that the sap6 is the major hyphal tip located sap protein under thp-1 phagocytosis. the sap6-deleted strains (δsap6,δsap4/6,and δsap5/6) appeared slower growth on congo red containing solid medium at 25°c,and the growth defect was exacerbated when cultured at 37°c in congo red or sds containing medium. in addition,more proteins were secreted from δsap6 strain and the β-mercaptoethanol (β-me) extractable surface proteins from δsap6 mutant were more abundant than that of extracted from wild type strain,which included the plasma membrane protein (pma1p),the er-chaperone protein (kar2p),the protein transport-related protein (arf1p),the cytoskeleton protein (act1),and the mitochondrial outer membrane protein (porin 1). moreover,the cell surface accessibility was increased in sap6-deleted strains. conclusion: from these results,we speculated that the cell surface constitution of c. albicans δsap6 strain was defect. this may cause the more accessible of β-me to disulfide-bridged cell surface components and may weaken the resistance of δsap6 strain encountering phagocytosis of thp-1 cells. sap6 protein displays a significant function involving in maintenance the cell surface integrity. © 2013 buu and chen; licensee biomed central ltd.