Institute of Molecular and Cellular Biology, National Tsing Hua University, Hsinchu, Taiwan.
PLoS One. 2011;6(6):e21394. doi: 10.1371/journal.pone.0021394. Epub 2011 Jun 21.
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, Xog1p(90-115), 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.
白色念珠菌是人类主要的真菌病原体。其与宿主细胞表面的黏附是黏膜感染过程中的第一步关键步骤。抗菌肽在针对白色念珠菌感染的黏膜固有免疫的第一道防线中发挥着重要作用。LL-37 是人类抗菌肽家族中唯一的一员，通常在包括上皮细胞在内的各种组织中表达。我们之前的研究表明，LL-37 可显著减少白色念珠菌对塑料、口腔表皮 OECM-1 细胞和雌性 BALB/c 小鼠膀胱的黏附。LL-37 抑制细胞黏附的作用是通过 LL-37 与细胞壁碳水化合物的结合来实现的。在这里，我们表明 LL-37-细胞壁蛋白复合物的形成可能抑制白色念珠菌对聚苯乙烯的黏附。通过噬菌体展示和 ELISA，我们鉴定出 10 个可以与 LL-37 结合的肽序列。BLAST 搜索显示，在主要的白色念珠菌细胞壁β-1,3-外葡聚糖酶 Xog1p 中有 4 个序列与从 10 个生物淘选肽衍生的共识序列高度相似。Xog1p 衍生肽 Xog1p(90-115)和重组 Xog1p 与 LL-37 结合，从而逆转了 LL-37 对白色念珠菌黏附的抑制作用。LL-37 降低了 Xog1p 的活性，从而中断了细胞壁重塑。此外，XOG1 或另一个β-1,3-外葡聚糖酶编码基因 EXG2 的缺失表明，只有当 XOG1 缺失时，细胞外葡聚糖酶活性、细胞黏附和 LL-37 结合才会减少。针对 Xog1p 的抗体也减少了细胞黏附。这些数据表明，最初从 LL-37 结合中鉴定出的 Xog1p 在白色念珠菌黏附聚苯乙烯方面发挥作用，并且通过直接或间接方式推断与宿主细胞附着。靶向 Xog1p 的化合物可能被用作预防白色念珠菌感染的药物。此外，LL-37 可能被用于筛选参与真菌细胞黏附的其他细胞壁成分。
