Atypical G protein signaling in Cryptococcus neoformans

描述（由申请人提供）：异三聚体G蛋白在人类致病性真菌新隐球菌中起重要的调节作用。G1亚基Gpa1控制着一个保守的camp依赖性信号通路，该通路调节毒力，但Gpa1异三聚体G蛋白复合物的必要成分尚不清楚。我们以Gpa1为蛋白诱饵，通过酵母双杂交筛选，鉴定出一种新的G2样/RACK1蛋白Gib2，该蛋白通过与Gpa1和G3亚基Gpg1和Gpg2结合而具有G2样功能。此外，我们发现，在gpa1突变株中，Gib2通过调节细胞内cAMP调节毒力因子黑色素和荚膜的形成，并且Gib2在不同血清型中表现出共同的和不同的功能：在变体新生生物中必不可少，但在变体grubii中则需要完全的毒力。我们提出了四个特定的目标来描述Gib2在cAMP调控中作为非典型G2、毒力因子和多功能蛋白的作用机制。鉴定和表征Gib2介导的非典型G蛋白信号和Gib2功能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。

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.