Calcium-binding protein 4 (CABP4) can be found in retina and in the inner hair cells (IHC) of the cochlea [, ]. In retina CABP4 is essential for the development and maintenance of the mouse photoreceptor synapse []. It controls the continuous release of the glutamate neurotransmitter in dark state photoreceptor cells []by regulating L-type calcium channels (Cav1.4) [, , ]. In IHC it acts as an integral subunit and modulator of Cav channels [].
This entry represents protein unc-119 homologue A (UNC119) from vertebrates, also known as retinal protein 4 (RG4) [], and the homologue from Drosophila []. It is highly expressed in retinal photoreceptor inner segments and synaptic regions. Nevertheless, UNC119 has been detected in leukocytes (eosinophils), T-cells, lung fibroblasts, the adrenal glands, cerebellum and kidney. It interacts with several diverse proteins, such as Arf-like GTPases ARL2/ARL3 [, ]and the Ca2+-binding protein CaBP4 []. It has been shown to activate Src-type tyrosine kinases associated with the interleukin-5 receptor and the T-cell receptor. It is also required for G protein trafficking in sensory neurons [].Mutations in the UNC119 gene cause immunodeficiency 13 (IMD13), a rare and heterogeneous syndrome defined by a reproducible reduction in the CD4 T-lymphocyte count [].
