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.

Alzheimer’s Disease-Associated β-Amyloid Is Rapidly Seeded by Herpesviridae to Protect against Brain Infection

“…Consistent with specificity for Aβ binding, signal was attenuated for anti-Aβ immunodepleted culture samples and scrambled Aβ42 peptide. Competitive inhibition of pathogen binding by soluble microbial sugars is a hallmark for AMPs with activities mediated by lectin-like carbohydrate binding (Tsai et al, 2011b). Consistent with carbohydrate-mediated virus binding, the yeast polysaccharide mannan inhibited Aβ binding to immobilized HSV1 (Figure 3A).…”

“…However, carbohydrate-binding and fibrillization are considered normally protective activities among AMPs, playing key roles in microbial targeting and agglutination (Chu et al, 2012; Torrent et al, 2012; Tsai et al, 2011a, b; Yount et al, 2006). Data are consistent with Aβ’s carbohydrate-binding activity mediating targeting and binding of viral surface glycoproteins (Figure 3).…”

LL37 and hBD-3 elevate the β-1,3-exoglucanase activity of Candida albicans Xog1p, resulting in reduced fungal adhesion to plastic

“…The AMP LL37 is also a broad-spectrum antimicrobial that is active against Gram-positive and Gramnegative bacteria and pathogenic fungi [33]. We also found that C. albicans cell-wall Xog1p is an LL37 receptor [36], which suggested that LL37 may prevent C. albicans-host cell interactions. We previously showed that LL37 interacts with C. albicans cell-wall carbohydrates and reduces C. albicans adhesion to plastic and mouse bladders [35].…”

Glucanase Induces Filamentation of the Fungal Pathogen Candida albicans

“…C. albicans possesses three cell wall related exo-beta-1, 3-glucanases, Xog1, Exg2, and Spr1 [11]. CAMP65 was also identified as a putative beta -glucanase and is required for hyphal morphogenesis [12].…”