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Src homology 3 domain of the Tight junction proteins, Zonula occludens (ZO) proteins ZO proteins are scaffolding proteins that associate with each other and with other proteins of the tight junction, zonula adherens, and gap junctions. They play roles in regulating cytoskeletal dynamics at these cell junctions. They are considered members of the MAGUK (membrane-associated guanylate kinase) protein family, which is characterized by the presence of a core of three domains: PDZ, SH3, and guanylate kinase (GuK). The GuK domain in MAGUK proteins is enzymatically inactive; instead, the domain mediates protein-protein interactions and associates intramolecularly with the SH3 domain. Vertebrates contain three ZO proteins (ZO-1, ZO-2, and ZO-3) with redundant and non-redundant roles. They contain three PDZ domains, followed by SH3 and GuK domains; in addition, ZO-1 and ZO-2 contains a proline-rich (PR) actin binding domain at the C-terminus while ZO-3 contains this PR domain between the second and third PDZ domains. The C-terminal regions of the three ZO proteins are unique. The SH3 domain of ZO-1 has been shown to bind ZONAB, ZAK, afadin, and Galpha12. SH3 domains are protein interaction domains that bind to proline-rich ligands with moderate affinity and selectivity, preferentially to PxxP motifs. They play versatile and diverse roles in the cell including the regulation of enzymes, changing the subcellular localization of signaling pathway components, and mediating the formation of multiprotein complex assemblies. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",