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C2 domain found in Human protein Kibra Kibra is thought to be a regulator of the Salvador (Sav)/Warts (Wts)/Hippo (Hpo) (SWH) signaling network, which limits tissue growth by inhibiting cell proliferation and promoting apoptosis. The core of the pathway consists of a MST and LATS family kinase cascade that ultimately phosphorylates and inactivates the YAP/Yorkie (Yki) transcription coactivator. The FERM domain proteins Merlin (Mer) and Expanded (Ex) are part of the upstream regulation controlling pathway mechanism. Kibra colocalizes and associates with Mer and Ex and is thought to transduce an extracellular signal via the SWH network. The apical scaffold machinery that contains Hpo, Wts, and Ex recruits Yki to the apical membrane facilitating its inhibitory phosphorlyation by Wts. Since Kibra associates with Ex and is apically located it is hypothesized that KIBRA is part of the scaffold, helps in the Hpo/Wts complex, and helps recruit Yki for inactivation that promotes SWH pathway activity. Kibra contains two amino-terminal WW domains, an internal C2-like domain, and a carboxy-terminal glutamic acid-rich stretch. The C2 domain was first identified in PKC. C2 domains fold into an 8-standed beta-sandwich that can adopt 2 structural arrangements: Type I and Type II, distinguished by a circular permutation involving their N- and C-terminal beta strands. Many C2 domains are Ca2+-dependent membrane-targeting modules that bind a wide variety of substances including bind phospholipids, inositol polyphosphates, and intracellular proteins. Most C2 domain proteins are either signal transduction enzymes that contain a single C2 domain, such as protein kinase C, or membrane trafficking proteins which contain at least two C2 domains, such as synaptotagmin 1. However, there are a few exceptions to this including RIM isoforms and some splice variants of piccolo/aczonin and intersectin which only have a single C2 domain. C2 domains with a calcium binding region have negatively charged residues, primarily aspartates, that serve as ligands for calcium ions. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",