Howlett Alyson C, Gray Amy J, Hunter Jesse M, Willardson Barry M
From the Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602.
From the Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602.
J Biol Chem. 2009 Jun 12;284(24):16386-16399. doi: 10.1074/jbc.M900800200. Epub 2009 Apr 17.
The G protein betagamma subunit dimer (Gbetagamma) and the Gbeta5/regulator of G protein signaling (RGS) dimer play fundamental roles in propagating and regulating G protein pathways, respectively. How these complexes form dimers when the individual subunits are unstable is a question that has remained unaddressed for many years. In the case of Gbetagamma, recent studies have shown that phosducin-like protein 1 (PhLP1) works as a co-chaperone with the cytosolic chaperonin complex (CCT) to fold Gbeta and mediate its interaction with Ggamma. However, it is not known what fraction of the many Gbetagamma combinations is assembled this way or whether chaperones influence the specificity of Gbetagamma dimer formation. Moreover, the mechanism of Gbeta5-RGS assembly has yet to be assessed experimentally. The current study was undertaken to directly address these issues. The data show that PhLP1 plays a vital role in the assembly of Ggamma2 with all four Gbeta1-4 subunits and in the assembly of Gbeta2 with all twelve Ggamma subunits, without affecting the specificity of the Gbetagamma interactions. The results also show that Gbeta5-RGS7 assembly is dependent on CCT and PhLP1, but the apparent mechanism is different from that of Gbetagamma. PhLP1 seems to stabilize the interaction of Gbeta5 with CCT until Gbeta5 is folded, after which it is released to allow Gbeta5 to interact with RGS7. These findings point to a general role for PhLP1 in the assembly of all Gbetagamma combinations and suggest a CCT-dependent mechanism for Gbeta5-RGS7 assembly that utilizes the co-chaperone activity of PhLP1 in a unique way.
G蛋白βγ亚基二聚体（Gβγ）和Gβ5/鸟苷酸结合蛋白信号调节因子（RGS）二聚体分别在G蛋白信号通路的传导和调节中发挥着重要作用。当各个亚基不稳定时，这些复合物如何形成二聚体，这一问题多年来一直未得到解决。就Gβγ而言，最近的研究表明，类光感受器蛋白1（PhLP1）作为一种共伴侣蛋白，与胞质伴侣蛋白复合物（CCT）共同作用，折叠Gβ并介导其与Gγ的相互作用。然而，尚不清楚众多Gβγ组合中有多大比例是以这种方式组装的，也不清楚伴侣蛋白是否会影响Gβγ二聚体形成的特异性。此外，Gβ5-RGS组装的机制尚未通过实验进行评估。当前的这项研究旨在直接解决这些问题。数据表明，PhLP1在Gγ2与所有4种Gβ1-4亚基的组装以及Gβ2与所有12种Gγ亚基的组装过程中发挥着至关重要的作用，且不影响Gβγ相互作用的特异性。结果还表明，Gβ5-RGS7的组装依赖于CCT和PhLP1，但其明显机制与Gβγ不同。PhLP1似乎会稳定Gβ5与CCT的相互作用，直到Gβ5折叠完成，之后它会被释放，使Gβ5能够与RGS7相互作用。这些发现表明PhLP1在所有Gβγ组合的组装中具有普遍作用，并提示了一种依赖于CCT的Gβ5-RGS7组装机制，该机制以独特的方式利用了PhLP1的共伴侣活性。
