Characterizing the role of cell-wall β-1,3-exoglucanase Xog1p in Candida albicans Adhesion by the human Antimicrobial Peptide LL-37

Abstract

Candida albicans is the major fungal pathogen of humans. Its adhesion to host-cell surfaces is the first critical step during mucosal infection. Antimicrobial peptides play important roles in the first line of mucosal immunity against C. albicans infection. LL-37 is the only member of the human cathelicidin antimicrobial peptide family and is commonly expressed in various tissues, including epithelium. We previously showed that LL-37 significantly reduced C. albicans adhesion to plastic, oral epidermoid OECM-1 cells, and urinary bladders of female BALB/c mice. The inhibitory effect of LL-37 on cell adhesion occurred via the binding of LL-37 to cell-wall carbohydrates. Here we showed that formation of LL-37-cell-wall protein complexes potentially inhibits C. albicans adhesion to polystyrene. Using phage display and ELISA, we identified 10 peptide sequences that could bind LL-37. A BLAST search revealed that four sequences in the major C. albicans cell-wall β-1,3-exoglucanase, Xog1p, were highly similar to the consensus sequence derived from the 10 biopanned peptides. One Xog1p-derived peptide, Xog1p90-115, and recombinant Xog1p associated with LL-37, thereby reversing the inhibitory effect of LL-37 on C. albicans adhesion. LL-37 reduced Xog1p activity and thus interrupted cell-wall remodeling. Moreover, deletion of XOG1 or another β-1,3-exoglucanase-encoding gene EXG2 showed that only when XOG1 was deleted did cellular exoglucanase activity, cell adhesion and LL-37 binding decrease. Antibodies against Xog1p also decreased cell adhesion. These data reveal that Xog1p, originally identified from LL-37 binding, has a role in C. albicans adhesion to polystyrene and, by inference, attach to host cells via direct or indirect manners. Compounds that target Xog1p might find use as drugs that prevent C. albicans infection. Additionally, LL-37 could potentially be used to screen for other cell-wall components involved in fungal cell adhesion. © 2011 Tsai et al.