School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, Scotland, UK.
J Biol Chem. 2010 Apr 16;285(16):12087-95. doi: 10.1074/jbc.M109.081513. Epub 2010 Feb 17.
The cell wall proteins of fungi are modified by N- and O-linked mannosylation and phosphomannosylation, resulting in changes to the physical and immunological properties of the cell. Glycosylation of cell wall proteins involves the activities of families of endoplasmic reticulum and Golgi-located glycosyl transferases whose activities are difficult to infer through bioinformatics. The Candida albicans MNT1/KRE2 mannosyl transferase family is represented by five members. We showed previously that Mnt1 and Mnt2 are involved in O-linked mannosylation and are required for virulence. Here, the role of C. albicans MNT3, MNT4, and MNT5 was determined by generating single and multiple MnTDelta null mutants and by functional complementation experiments in Saccharomyces cerevisiae. CaMnt3, CaMnt4, and CaMnt5 did not participate in O-linked mannosylation, but CaMnt3 and CaMnt5 had redundant activities in phosphomannosylation and were responsible for attachment of approximately half of the phosphomannan attached to N-linked mannans. CaMnt4 and CaMnt5 participated in N-mannan branching. Deletion of CaMNT3, CaMNT4, and CaMNT5 affected the growth rate and virulence of C. albicans, affected the recognition of the yeast by human monocytes and cytokine stimulation, and led to increased cell wall chitin content and exposure of beta-glucan at the cell wall surface. Therefore, the MNT1/KRE2 gene family participates in three types of protein mannosylation in C. albicans, and these modifications play vital roles in fungal cell wall structure and cell surface recognition by the innate immune system.
真菌细胞壁蛋白通过 N-和 O-链接甘露糖基化和磷酸甘露糖基化修饰，从而改变细胞的物理和免疫学特性。细胞壁蛋白的糖基化涉及内质网和高尔基体定位的糖基转移酶家族的活性，这些酶的活性很难通过生物信息学推断出来。白色念珠菌 MNT1/KRE2 甘露糖基转移酶家族由五个成员组成。我们之前表明，Mnt1 和 Mnt2 参与 O-链接甘露糖基化，并且是毒力所必需的。在这里，通过生成单个和多个 MnTDelta 缺失突变体以及在酿酒酵母中的功能互补实验，确定了白色念珠菌 MNT3、MNT4 和 MNT5 的作用。CaMnt3、CaMnt4 和 CaMnt5 不参与 O-链接甘露糖基化，但 CaMnt3 和 CaMnt5 在磷酸甘露糖基化中具有冗余活性，负责附着在 N-链接甘露糖上的大约一半磷酸甘露聚糖。CaMnt4 和 CaMnt5 参与 N-甘露聚糖分支。CaMNT3、CaMNT4 和 CaMNT5 的缺失影响白色念珠菌的生长速度和毒力，影响人单核细胞对酵母的识别和细胞因子刺激，并导致细胞壁几丁质含量增加和β-葡聚糖在细胞壁表面暴露。因此，MNT1/KRE2 基因家族参与白色念珠菌中三种类型的蛋白质甘露糖基化，这些修饰在真菌细胞壁结构和固有免疫系统对细胞表面的识别中起着至关重要的作用。
