Gib2, a novel Gβ-like/RACK1 homolog, functions as a Gβ subunit in cAMP signaling and is essential in Cryptococcus neoformans
Gib2, a novel Gβ-like/RACK1 homolog, functions as a Gβ subunit in cAMP signaling and is essential in Cryptococcus neoformans
复制标题
DOI：
10.1074/jbc.m602768200
复制
发表时间：
2006-10-27
影响因子：
4.8
通讯作者：
Wang, Ping
中科院分区：
文献类型：
--
作者：
Palmer, Daniel A.;Thompson, Jill K.;Wang, Ping
典型G蛋白是异三聚体，由α、β和γ亚基组成。尽管真菌中有多个G α亚基，但每个物种中只有一个G β亚基，这表明在这个多样化的真核生物群体中存在非传统的G蛋白信号。利用在cAMP信号中起作用的G α亚基Gpa1作为诱饵，在双杂交筛选中，我们从人类致病性真菌新隐球菌中鉴定出一种新的G β样/RACK1蛋白同源物Gib2。Gib2包含一个7个WD-40重复基序，预计会形成β转导素特征的7叶β螺旋桨结构。Gib2还分别与两个G β亚基同源物Gpg1和Gpg2相互作用，类似于传统的G β亚基Gpb1。与gpa1的过表达促进交配反应相反，Gib2的过度产生抑制gpa1突变在黑化和被囊形成方面的缺陷，这些表型由cAMP信号调节并与毒力相关。此外，由于反义抑制而导致的Gib2缺失会导致严重的生长缺陷，这表明Gib2是必不可少的。最后，Gib2也被证明与Gpa1-cAMP信号的下游靶点Smg1和蛋白激酶C同源物Pkc1相互作用，表明Gib2也是一个多功能的rack1样蛋白。
Canonical G proteins are heterotrimeric, consisting of alpha, beta, and gamma subunits. Despite multiple G alpha subunits functioning in fungi, only a single G beta subunit per species has been identified, suggesting that non-conventional G protein signaling exists in this diverse group of eukaryotic organisms. Using the G alpha subunit Gpa1 that functions in cAMP signaling as bait in a two-hybrid screen, we have identified a novel G beta-like/RACK1 protein homolog, Gib2, from the human pathogenic fungus Cryptococcus neoformans. Gib2 contains a seven WD-40 repeat motif and is predicted to form a seven-bladed beta propeller structure characteristic of beta transducins. Gib2 is also shown to interact, respectively, with two G gamma subunit homologs, Gpg1 and Gpg2, similar to the conventional G beta subunit Gpb1. In contrast to Gpb1 whose overexpression promotes mating response, overproduction of Gib2 suppresses defects of gpa1 mutation in both melanization and capsule formation, the phenotypes regulated by cAMP signaling and associated with virulence. Furthermore, depletion of Gib2 by antisense suppression results in a severe growth defect, suggesting that Gib2 is essential. Finally, Gib2 is shown to also physically interact with a downstream target of Gpa1-cAMP signaling, Smg1, and the protein kinase C homolog Pkc1, indicating that Gib2 is also a multifunctional RACK1-like protein.