Willger Sven D, Ernst Joachim F, Alspaugh J Andrew, Lengeler Klaus B
Institut für Mikrobiologie, Molekulare Mykologie, Heinrich-Heine-Universität, Düsseldorf, Germany.
PLoS One. 2009 Jul 27;4(7):e6321. doi: 10.1371/journal.pone.0006321.
Protein-O-mannosyltransferases (Pmt's) catalyze the initial step of protein-O-glycosylation, the addition of mannose residues to serine or threonine residues of target proteins.
METHODOLOGY/PRINCIPAL FINDINGS: Based on protein similarities, this highly conserved protein family can be divided into three subfamilies: the Pmt1 sub-family, the Pmt2 sub-family and the Pmt4 sub-family. In contrast to Saccharomyces cerevisiae and Candida albicans, but similar to filamentous fungi, three putative PMT genes (PMT1, PMT2, and PMT4) were identified in the genome of the human fungal pathogen Cryptococcus neoformans. Similar to Schizosaccharomyces pombe and C. albicans, C. neoformans PMT2 is an essential gene. In contrast, the pmt1 and pmt4 single mutants are viable; however, the pmt1/pmt4 deletions are synthetically lethal. Mutation of PMT1 and PMT4 resulted in distinct defects in cell morphology and cell integrity. The pmt1 mutant was more susceptible to SDS medium than wild-type strains and the mutant cells were enlarged. The pmt4 mutant grew poorly on high salt medium and demonstrated abnormal septum formation and defects in cell separation. Interestingly, the pmt1 and pmt4 mutants demonstrated variety-specific differences in the levels of susceptibility to osmotic and cell wall stress. Delayed melanin production in the pmt4 mutant was the only alteration of classical virulence-associated phenotypes. However, the pmt1 and pmt4 mutants showed attenuated virulence in a murine inhalation model of cryptococcosis.
CONCLUSION/SIGNIFICANCE: These findings suggest that C. neoformans protein-O-mannosyltransferases play a crucial role in maintaining cell morphology, and that reduced protein-O-glycosylation leads to alterations in stress resistance, cell wall composition, cell integrity, and survival within the host.
蛋白质 O-甘露糖基转移酶（Pmt）催化蛋白质 O-糖基化的起始步骤，即将甘露糖残基添加到靶蛋白的丝氨酸或苏氨酸残基上。
方法/主要发现：基于蛋白质相似性，这个高度保守的蛋白质家族可分为三个亚家族：Pmt1 亚家族、Pmt2 亚家族和 Pmt4 亚家族。与酿酒酵母和白色念珠菌不同，但与丝状真菌相似，在人类真菌病原体新型隐球菌的基因组中鉴定出三个假定的 PMT 基因（PMT1、PMT2 和 PMT4）。与粟酒裂殖酵母和白色念珠菌相似，新型隐球菌 PMT2 是一个必需基因。相比之下，pmt1 和 pmt4 单突变体是可行的；然而，pmt1/pmt4 缺失是合成致死的。PMT1 和 PMT4 的突变导致细胞形态和细胞完整性出现明显缺陷。pmt1 突变体比野生型菌株对 SDS 培养基更敏感，且突变细胞增大。pmt4 突变体在高盐培养基上生长不良，表现出异常的隔膜形成和细胞分离缺陷。有趣的是，pmt1 和 pmt4 突变体在对渗透和细胞壁应激的敏感性水平上表现出种属特异性差异。pmt4 突变体中黑色素产生延迟是经典毒力相关表型的唯一改变。然而，pmt1 和 pmt4 突变体在小鼠隐球菌病吸入模型中显示出毒力减弱。
结论/意义：这些发现表明，新型隐球菌蛋白质 O-甘露糖基转移酶在维持细胞形态方面起关键作用，并且蛋白质 O-糖基化减少会导致应激抗性、细胞壁组成、细胞完整性以及在宿主体内的存活发生改变。
