Department of Biotechnology, Sri Ramachandra Institute of Higher Education and Research (DU), Porur, Chennai 600116, Tamil Nadu, India.
Wellcome Trust Research Laboratory, Division of Gastrointestional Sciences, Christian Medical College and Hospital, Vellore 632004, Tamil Nadu, India.
Curr Comput Aided Drug Des. 2022;18(5):327-336. doi: 10.2174/1573409918666220818120645.
BACKGROUND & OBJECTIVE: Candida albicans (C.-P. Robin) Berkhout, the pathogenic yeasts' ability to transform from yeast to hyphal forms in the bloodstream is essential during systemic infections. Among the several virulence factors studied, secreted aspartic proteinases (SAPs) involved in hyphal penetration are targets of putative hyphal inhibitors. Upregulation of SAP6 gene, (two-to 31- fold high) during budded to hyphal transition and lack of studies on its inhibition, prompted us to investigate this particular protein using in silico tools.
Hyphal inhibition of germinating yeast cells by melianone, a triterpenoid, from Swietenia mahagoni (L.) Jacq. (Meliaceae) was observed at 0.1 μM (IC50). One of the targets of putative hyphal inhibitors, SAP, was assayed and for the first time, 50 % of the biological SAP activity was found to be inhibited by melianone at 0.125 μM. This data on SAP inhibition led us to analyse the 3-dimensional structure for SAP6 protein that was constructed through a combination of homology modelling and ab-initio method (Phyre2) and validated before performing Induced Fit Docking (IFD). Melianone formed H-bond and hydrophobic interactions with the crucial residues (ASP108, TYR160, ALA161, ASP162, ASP294, THR297, ASP379) in the catalytic site of SAP6 with a glide energy (-)54.9327 kcal/mol upon Induced Fit Docking (IFD).
We report here for the first time on the SAP inhibitory ability of melianone at 0.125 uM. Being a small molecular mass inhibitor, binding with high affinity to the S3 pocket sites of SAP proteins provides evidence for pre-clinical testing of such compounds against fungal pathogens. The study is a valuable insight for further research on novel and effective inhibitors targeting SAP.
白色念珠菌（C.-P. Robin）Berkhout，致病性酵母在血流中从酵母形态转变为菌丝形态的能力在全身感染过程中至关重要。在研究的几种毒力因子中，参与菌丝穿透的分泌天冬氨酸蛋白酶（SAP）是潜在菌丝抑制剂的靶标。在芽殖到菌丝过渡期间，SAP6 基因的上调（高达 2-31 倍），以及缺乏对其抑制作用的研究，促使我们使用计算机工具研究这种特殊的蛋白质。
在 0.1μM（IC50）时，来自 Swietenia mahagoni（L.）Jacq.（Meliaceae）的三萜类化合物 melianone 抑制发芽酵母细胞的菌丝形成。作为潜在菌丝抑制剂的靶标之一，SAP 进行了测定，结果首次发现，melianone 在 0.125μM 时抑制了 50%的生物学 SAP 活性。关于 SAP 抑制的数据促使我们分析 SAP6 蛋白的三维结构，该结构通过同源建模和从头计算方法（Phyre2）构建，并在进行诱导契合对接（IFD）之前进行了验证。Melianone 与 SAP6 催化位点的关键残基（ASP108、TYR160、ALA161、ASP162、ASP294、THR297、ASP379）形成氢键和疏水相互作用，在诱导契合对接（IFD）时 Glide 能量为（-）54.9327 kcal/mol。
我们首次报道了 melianone 在 0.125μM 时对 SAP 的抑制能力。作为一种小分子质量抑制剂，它与 SAP 蛋白的 S3 口袋位点高亲和力结合，为针对真菌病原体进行此类化合物的临床前测试提供了证据。该研究为进一步研究针对 SAP 的新型有效抑制剂提供了有价值的见解。
