RING finger, HC subclass, found in E3 ubiquitin-protein ligase Hakai, zinc finger protein 645 (ZNF645), and similar proteins
Hakai, also known as Casitas B-lineage lymphoma-transforming sequence-like protein 1, RING finger protein 188 (RNF188), or c-Cbl-like protein 1 (CBLL1), is an E3 ubiquitin ligase that disrupts cell-cell contacts in epithelial cells and is upregulated in human colon and gastric adenocarcinomas. It was identified to mediate the posttranslational downregulation of E-cadherin (CDH1), a major component of adherens junctions in epithelial cells and a potent tumor suppressor. It also promotes ubiquitination of several other tyrosine-phosphorylated Src substrates, including cortactin (CTTN) and DOK1. Hakai acts as a homodimer with a novel HYB (Hakai pTyr-binding) domain that forms a phosphotyrosine-binding pocket upon, and consists of a pair of monomers arranged in an anti-parallel configuration. Each monomer contains a C3HC4-type RING-HC finger and a short pTyr-B domain that incorporates a novel, atypical C2H2-type Zn-finger coordination motif. Both domains are important for dimerization. ZNF645 is a novel testis-specific E3 ubiquitin-protein ligase that plays a role in sperm production and quality control. It has a structure similar to that of the c-Cbl-like protein Hakai. In contrast to Hakai, its HYB domain demonstrates different target specificities. It interacts with v-Src-phosphorylated E-cadherin, but not to cortactin.