Medical Faculty, Institute of Biochemistry and Molecular Biology II, University Hospital Düsseldorf, Heinrich Heine University Düsseldorf, 40225 Düsseldorf, Germany.
Department of Pathology and Molecular Medicine, McMaster University, Hamilton, ON L8S 4L8, Canada.
Int J Mol Sci. 2021 Nov 22;22(22):12596. doi: 10.3390/ijms222212596.
IQ motif-containing GTPase-activating proteins (IQGAPs) modulate a wide range of cellular processes by acting as scaffolds and driving protein components into distinct signaling networks. Their functional states have been proposed to be controlled by members of the RHO family of GTPases, among other regulators. In this study, we show that IQGAP1 and IQGAP2 can associate with CDC42 and RAC1-like proteins but not with RIF, RHOD, or RHO-like proteins, including RHOA. This seems to be based on the distribution of charged surface residues, which varies significantly among RHO GTPases despite their high sequence homology. Although effector proteins bind first to the highly flexible switch regions of RHO GTPases, additional contacts outside are required for effector activation. Sequence alignment and structural, mutational, and competitive biochemical analyses revealed that RHO GTPases possess paralog-specific residues outside the two highly conserved switch regions that essentially determine the selectivity of RHO GTPase binding to IQGAPs. Amino acid substitution of these specific residues in RHOA to the corresponding residues in RAC1 resulted in RHOA association with IQGAP1. Thus, electrostatics most likely plays a decisive role in these interactions.
富含 IQ 基序的 GTP 酶激活蛋白（IQGAPs）通过作为支架并将蛋白质成分驱动到不同的信号网络中来调节广泛的细胞过程。它们的功能状态被认为受到 RHO 家族 GTP 酶等调节剂的控制。在这项研究中，我们表明 IQGAP1 和 IQGAP2 可以与 CDC42 和 RAC1 样蛋白结合，但不能与 RIF、RHOD 或 RHO 样蛋白（包括 RHOA）结合。这似乎基于带电表面残基的分布，尽管 RHO GTPases 具有高度的序列同源性，但它们之间的差异很大。尽管效应蛋白首先结合到 RHO GTPases 的高度灵活的开关区域，但还需要额外的外部接触才能激活效应蛋白。序列比对和结构、突变和竞争生化分析表明，RHO GTPases 在两个高度保守的开关区域之外具有独特的残基，这些残基基本上决定了 RHO GTPase 与 IQGAPs 的结合选择性。将 RHOA 中的这些特定残基突变为 RAC1 中的相应残基，导致 RHOA 与 IQGAP1 结合。因此，静电作用很可能在这些相互作用中起决定性作用。
