Since this area of the protein is conserved in amino acid sequence and structure, it can be characterized by function or binding partner. IQGAP1 has 5 well-known domains separated by other amino acids. Starting at the N-terminus (or front of the protein), IQGAP1 contains a calponin homology domain (CHD), which mediates actin-binding and binds calponin. The WW, or poly-proline protein-protein domain, so named because of two functionally conserved tryptophans, W, is a protein-protein interaction domain that associates with proline-rich regions of other proteins. The WW domain is followed by 4 IQ motifs which form an IQ domain. This domain binds calmodulin, a protein known as a calcium sensor that can bind and regulate many target proteins. A GRD (rasGAP-related domain) follows the IQ domain. This domain is highly similar to the functional subunit of Ras GTPase-activating proteins (GAPs) and was thus thought to have GAP function. IQGAP1 does bind Rho GTPases CDC42 and RAC1, however, IQGAP1 is unusual in that it actually has no GAP function, and instead stabilizes the GTP-bound proteins in their active state. Finally, IQGAP1 has a RasGAP_c carboxy terminal sequence important for binding Beta-catenin and E-cadherin. Homologues of IQGAP1 are known in species as divergent as yeast, worms, and humans (as well as other mammals), though the domains are not always highly conserved. IQGAP1 is the most well studied member of the IQGAP family of scaffold proteins. The two other members of the family include IQGAP2 and IQGAP3 which have far more restricted expression patterns in comparison with IQGAP1. IQGAP2 is found in the liver, stomach, and platelets and is 62% identical to IQGAP1, but appears to have a drastically divergent function in terms of pathology. In the brain, IQGAP3 appears to play an important role in neuronal morphogenesis. This gene encodes a member of the IQGAP family. The protein contains four IQ domains, one calponin homology domain, one Ras-GAP domain and one WW domain. It interacts with components of the cytoskeleton such as the formin Dia1 (mDia1), with cell adhesion molecules (CAMs), and with several signaling molecules to regulate cell morphology and motility.