Baker Lorina G, Specht Charles A, Donlin Maureen J, Lodge Jennifer K
Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, Saint Louis, MO 63104, USA.
Eukaryot Cell. 2007 May;6(5):855-67. doi: 10.1128/EC.00399-06. Epub 2007 Mar 30.
Cryptococcus neoformans is an opportunistic fungal pathogen that causes cryptococcal meningoencephalitis, particularly in immunocompromised patients. The fungal cell wall is an excellent target for antifungal therapies as it is an essential organelle that provides cell structure and integrity, it is needed for the localization or attachment of known virulence factors, including the polysaccharide capsule, melanin, and phospholipase, and it is critical for host-pathogen interactions. In C. neoformans, chitosan produced by the enzymatic removal of acetyl groups from nascent chitin polymers has been implicated as an important component of the vegetative cell wall. In this study, we identify four putative chitin/polysaccharide deacetylases in C. neoformans. We have demonstrated that three of these deacetylases, Cda1, Cda2, and Cda3, can account for all of the chitosan produced during vegetative growth in culture, but the function for one, Fpd1, remains undetermined. The data suggest a model for chitosan production in vegetatively growing C. neoformans where the three chitin deacetylases convert chitin generated by the chitin synthase Chs3 into chitosan. Utilizing a collection of chitin/polysaccharide deacetylase deletion strains, we determined that during vegetative growth, chitosan helps to maintain cell integrity and aids in bud separation. Additionally, chitosan is necessary for maintaining normal capsule width and the lack of chitosan results in a "leaky melanin" phenotype. Our analysis indicates that chitin deacetylases and the chitosan made by them may prove to be excellent antifungal targets.
新型隐球菌是一种机会性真菌病原体,可引起隐球菌性脑膜脑炎,尤其是在免疫功能低下的患者中。真菌细胞壁是抗真菌治疗的理想靶点,因为它是一种重要的细胞器,提供细胞结构和完整性,已知的毒力因子(包括多糖荚膜、黑色素和磷脂酶)的定位或附着需要它,并且它对宿主 - 病原体相互作用至关重要。在新型隐球菌中,由新生几丁质聚合物的乙酰基酶促去除产生的壳聚糖被认为是营养细胞壁的重要组成部分。在本研究中,我们鉴定了新型隐球菌中的四种假定的几丁质/多糖脱乙酰酶。我们已经证明,其中三种脱乙酰酶Cda1、Cda2和Cda3可以解释培养物营养生长期间产生的所有壳聚糖,但其中一种Fpd1的功能仍未确定。数据表明了一种在营养生长的新型隐球菌中产生壳聚糖的模型,其中三种几丁质脱乙酰酶将几丁质合酶Chs3产生的几丁质转化为壳聚糖。利用一组几丁质/多糖脱乙酰酶缺失菌株,我们确定在营养生长期间,壳聚糖有助于维持细胞完整性并有助于芽分离。此外,壳聚糖对于维持正常的荚膜宽度是必需的,并且缺乏壳聚糖会导致“黑色素渗漏”表型。我们的分析表明,几丁质脱乙酰酶及其产生的壳聚糖可能被证明是优秀的抗真菌靶点。