This entry represents the SH3 domain of MPP1, which is a ubiquitously-expressed scaffolding protein that plays roles in regulating neutrophil polarity, cell shape, hair cell development, and neural development and patterning of the retina [, ]. It was originally identified as an erythrocyte protein that stabilizes the actin cytoskeleton to the plasma membrane by forming a complex with 4.1R protein and glycophorin C [, ]. MPP1 belongs to the membrane-associated guanylate kinase (MAGUK) p55 subfamily.The membrane-associated guanylate kinase (MAGUK) p55 subfamily (also known as MPP subfamily) members include the Drosophila Stardust protein and its vertebrate homologues, MPP1-7. They contain the core of three domains characteristic of MAGUK (membrane-associated guanylate kinase) proteins: PDZ, SH3, and guanylate kinase (GuK). In addition, they also contain the Hook (Protein 4.1 Binding) motif in between the SH3 and GuK domains []. MPP2-7 have two additional L27 domains at their N terminus. The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain [].
