Tsai H, Bobek L A
Department of Oral Biology, School of Dental Medicine, State University of New York at Buffalo, 14214, USA.
Antimicrob Agents Chemother. 1997 Oct;41(10):2224-8. doi: 10.1128/AAC.41.10.2224.
Histatins are a group of small, cationic, antifungal peptides present in human saliva. A previous molecular modeling analysis suggested structural similarity between the Phe14-His15 and His18-His19 dipeptide sequences in histatin-5 (Hsn-5; a 24-amino-acid polypeptide) and the sequence of miconazole (one of the azole-based antifungal therapeutic agents), implying that the mechanisms of killing of Candida albicans by these two molecules may be similar. To further elaborate on this observation, we have produced two variants of Hsn-5 in which Phe14-His15 or His18-His19 dipeptide sequences were replaced by Ala-Ala (F14A/H15A and H18A/H19A) to eliminate the phenyl and imidazole rings of the side chains and assessed their candidacidal activities against C. albicans. In addition, we tested azole-resistant C. albicans and Candida glabrata strains for their susceptibilities to Hsn-5. Analysis of the purified recombinant proteins for their candidacidal activities indicated that both variants were significantly less effective (the molar concentrations required to kill half of the maximum number of cells [ED50s], approximately 67 and approximately 149 microM for F14A/H15A and H18A/H19A, respectively) than the unaltered Hsn-5 (ED50, approximately 8 microM) at killing C. albicans, suggesting that the two dipeptide sequences are important for the candidacidal activity of Hsn-5. Assessment of the candidacidal activity of Hsn-5 with the well-characterized azole-resistant strains of C. albicans and C. glabrata, however, suggested that the mode of action of histatins against Candida is distinct from that of azole-based antifungal agents because Hsn-5 kills both azole-sensitive and azole-resistant strains equally well.
组蛋白是存在于人类唾液中的一组小的阳离子抗真菌肽。先前的分子模拟分析表明，组蛋白-5（Hsn-5；一种24个氨基酸的多肽）中的Phe14-His15和His18-His19二肽序列与咪康唑（一种基于唑类的抗真菌治疗剂）的序列在结构上相似，这意味着这两种分子杀死白色念珠菌的机制可能相似。为了进一步阐述这一观察结果，我们制备了Hsn-5的两种变体，其中Phe14-His15或His18-His19二肽序列被Ala-Ala取代（F14A/H15A和H18A/H19A），以消除侧链中的苯基和咪唑环，并评估它们对白色念珠菌的杀念珠菌活性。此外，我们测试了耐唑类的白色念珠菌和光滑念珠菌菌株对Hsn-5的敏感性。对纯化的重组蛋白的杀念珠菌活性分析表明，与未改变的Hsn-5（ED50，约8 microM）相比，两种变体在杀死白色念珠菌方面的效果均显著降低（杀死半数最大细胞数所需的摩尔浓度[ED50s]，F14A/H15A和H18A/H19A分别约为67和约149 microM），这表明这两个二肽序列对Hsn-5的杀念珠菌活性很重要。然而，用特征明确的耐唑类白色念珠菌和光滑念珠菌菌株评估Hsn-5的杀念珠菌活性表明，组蛋白对念珠菌的作用方式与基于唑类的抗真菌剂不同，因为Hsn-5对唑类敏感和耐唑类菌株的杀伤效果相同。
