Table_2_Candida albicans Pma1p Contributes to Growth, pH Homeostasis, and Hyphal Formation.docx

Candida albicans occupies diverse ecological niches within the host and must tolerate a wide range of environmental pH. The plasma membrane H+-ATPase Pma1p is the major regulator of cytosolic pH in fungi. Pma1p extrudes protons from the cytosol to maintain neutral-to-alkaline pH and is a potential drug target due to its essentiality and fungal specificity. We characterized mutants in which one allele of PMA1 has been deleted and the other truncated by 18–38 amino acids. Increasing C-terminal truncation caused corresponding decreases in plasma membrane ATPase-specific activity and cytosolic pH. Pma1p is regulated by glucose: glucose rapidly activates the ATPase, causing a sharp increase in cytosolic pH. Increasing Pma1p truncation severely impaired this glucose response. Pma1p truncation also altered cation responses, disrupted vacuolar morphology and pH, and reduced filamentation competence. Early studies of cytosolic pH and filamentation have described a rapid, transient alkalinization of the cytosol preceding germ tube formation; Pma1p has been proposed as a regulator of this process. We find Pma1p plays a role in the establishment of cell polarity, and distribution of Pma1p is non-homogenous in emerging hyphae. These findings suggest a role of PMA1 in cytosolic alkalinization and in the specialized form of polarized growth that is filamentation.

白色念珠菌（Candida albicans）可定植于宿主内多种不同的生态位，且必须耐受大范围的环境pH波动。质膜H+-ATP酶Pma1p（plasma membrane H+-ATPase Pma1p）是真菌胞质pH的主要调控因子：Pma1p可将质子从胞质中排出，以维持中性至碱性的胞质pH；由于其必需性与真菌特异性，该酶亦是潜在的药物靶点。
我们对如下突变体开展了表征：其中PMA1基因的一个等位基因被敲除，另一个等位基因则被截短18~38个氨基酸。随着Pma1p C端截短程度增加，质膜ATP酶比活性与胞质pH均出现相应下降。
Pma1p的活性受葡萄糖调控：葡萄糖可快速激活该ATP酶，引发胞质pH的急剧升高；而Pma1p截短程度的增加则严重削弱了这一葡萄糖响应过程。此外，Pma1p截短还改变了细胞的阳离子响应、破坏了液泡形态与pH稳态，并降低了菌株的菌丝形成能力。
早期关于胞质pH与菌丝形成的研究曾报道，芽管形成前会出现胞质快速、短暂的碱化现象，并曾提出Pma1p是该过程的调控因子。我们的研究发现，Pma1p参与细胞极性的建立，且在新生菌丝中Pma1p的分布并不均匀。
上述研究结果表明，PMA1基因参与胞质碱化过程，并在菌丝形成这种特化的极性生长形式中发挥作用。