Atypical G protein signaling in Cryptococcus neoformans

描述（由申请人提供）：异源三聚体G蛋白在人类致病真菌新型隐球菌中起重要的调节作用。G1亚基Gpa 1控制一个保守的cAMP依赖性信号通路，调节毒力，但Gpa 1异源三聚体G蛋白复合物的必要组成部分是未知的。以Gpa 1为诱饵蛋白，通过酵母双杂交筛选，我们鉴定出一种新的G2样/RACK 1蛋白，Gib 2，它与Gpa 1和G3亚基Gpg 1和Gpg 2结合，具有G2样功能。此外，我们发现Gib 2通过调节gpa 1突变株细胞内cAMP来调节毒力因子黑色素和荚膜的形成，并且Gib 2在血清型之间表现出共享和不同的功能：在var. neoformans，但需要完全毒力的变种。grubii。提出了四个具体的目标来表征Gib 2作为非典型G2调节cAMP，作为毒力因子和作为多功能蛋白的机制。Gib 2介导的非典型G蛋白信号传导和Gib 2功能的鉴定和表征不仅对我们理解调节细胞生长、分化和发病机制的信号转导机制具有重要意义，而且对我们寻求抗真菌治疗的新靶点也具有重要意义。 相关性：新型隐球菌是一种常见的机会致病菌，可引起人类真菌性脑膜脑炎。G蛋白介导的信号转导在真菌的生理和致病过程中起着重要的调节作用。了解G蛋白信号传导的分子事件可能有助于揭示抗真菌治疗的新靶点。

DESCRIPTION (provided by applicant): The heterotrimeric G protein plays an important regulatory role in the human pathogenic fungus Cryptococcus neoformans. The G1 subunit Gpa1 governs a conserved cAMP-dependent signaling pathway that regulates virulence, but the necessary components of a Gpa1 heterotrimeric G protein complex are not known. Using Gpa1 as protein bait and through a yeast two-hybrid screen, we have identified a novel G2- like/RACK1 protein, Gib2, which exhibits a G2-like function by association with Gpa1 and G3 subunits Gpg1 and Gpg2. In addition, we found that Gib2 regulates formation of virulence factors melanin and capsule through modulation of intracellular cAMP in a gpa1 mutant strain, and Gib2 exhibits shared and distinct functions across serotypes: essential in var. neoformans, but required for full virulence of var. grubii. Four specific aims are proposed to characterize the mechanism by which Gib2 functions as an atypical G2 in regulation of cAMP, as a virulence factor, and as a multi-functional protein. Identification and characterization of Gib2-mediated atypical G protein signaling and Gib2 function is significant not only for our understanding of signal transduction mechanisms regulating cellular growth, differentiation, and pathogenesis but also in our pursuing of novel targets for antifungal therapy. Relevance: Cryptococcus neoformans is a prevalent opportunistic pathogen that causes fungal meningoencephalitis in humans. G protein-mediated signal transduction plays an important regulatory role in the physiology and pathogenesis of the fungus. Understanding the molecular events that underlie G protein signaling may help to reveal novel targets for antifungal therapy.