This domain can be found in the C terminus of the IQGAP family members, including human IQGAP1/2/3, S. cerevisiae Iqg1 and S. pombe Rng2. Some members function in cytoskeletal remodelling []. Human IQGAP1 is a scaffolding protein that can assemble multi-protein complexes involved in cell-cell interaction, cell adherence, and movement via actin/tubulin-based cytoskeletal reorganization []. IQGAP1 is also a regulator of the MAPK and Wnt/beta-catenin signaling pathways []. Iqg1 and Rng2 are required for actomyosin ring construction during cytokinesis [, ].
This entry includes MISP/MISP3 from animals. MISP is an actin-binding protein that functions in spindle orientation probably by linking the astral microtubules (MTs) to the actin cytoskeleton [, ]. It has been shown to regulate IQGAP1 and Cdc42 to ensure proper mitotic progression and correct spindle orientation []. The function of MISP3 is not clear.
The IQ motif is an extremely basic unit of about 23 amino acids, whose conserved core usually fits the consensus A-x(3)-I-Q-x(2)-F-R-x(4)-K-K. The IQ motif, which can be present in one or more copies, serves as a binding site for different EF-hand proteins including the essential and regulatory myosin light chains, calmodulin (CaM), and CaM-like proteins [, ].Many IQ motifs are protein kinase C (PKC) phosphorylation sites [, ].Resolution of the 3D structure of scallop myosin has shown that the IQ motif forms a basic amphipathic helix [].Some proteins known to contain an IQ motif are listed below:A number of conventional and unconventional myosins.Neuromodulin (GAP-43). This protein is associated with nerve growth. It is a major component of the motile "growth cones"that form the tips of elongating axons.Neurogranin (NG/p17). Acts as a "third messenger"substrate of protein kinase C-mediated molecular cascades during synaptic development and remodeling.Sperm surface protein Sp17.Ras GTPase-activating-like protein IQGAP1. IQGAP1 contains 4 IQ motifs.This entry covers the entire IQ motif.
