Evectins: Vesicular proteins that carry a pleckstrin homology domain and localize to post-Golgi membranes

Abstract

We have identified two vesicular proteins, designated evectin (evt)-1 and -2. These proteins are Ϸ Ϸ25 kDa in molecular mass, lack a cleaved N-terminal signal sequence, and appear to be inserted into membranes through a Cterminal hydrophobic anchor. They also carry a pleckstrin homology domain at their N termini, which potentially couples them to signal transduction pathways that result in the production of lipid second messengers. evt-1 is specific to the nervous system, where it is expressed in photoreceptors and myelinating glia, polarized cell types in which plasma membrane biosynthesis is prodigious and regulated; in contrast, evt-2 is widely expressed in both neural and nonneural tissues. In photoreceptors, evt-1 localizes to rhodopsin-bearing membranes of the post-Golgi, an important transport compartment for which specific molecular markers have heretofore been lacking. The structure and subcellular distribution of evt-1 strongly implicate this protein as a mediator of postGolgi trafficking in cells that produce large membrane-rich organelles. Its restricted cellular distribution and genetic locus make it a candidate gene for the inherited human retinopathy autosomal dominant familial exudative vitreoretinopathy and suggest that it also may be a susceptibility gene for multiple sclerosis.

Identification of pleckstrin-homology-domain-containing proteins with novel phosphoinositide-binding specificities

“…AAC39675), interacted with several phosphoinositides (Figure 2). The PH domain of a protein of unknown function, termed evectin-2, which localizes to post-Golgi membranes [25], showed a moderate affinity for PtdIns(3,4,5)P $ , but also interacted more weakly with several other phosphoinositides (Figure 2). None of the PH domains for which lipid-binding properties were investigated (as shown in Figure 2) interacted with phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine or phosphatidylinositol in the protein-lipid overlay assay (results not shown).…”

Phosphoinositide 3-kinase signaling in the vertebrate retina

“…Two other proteins with PH domains play potentially important roles in the retina. Evictin-1 can localize to rhodopsin-laden, postGolgi membranes in photoreceptor cells, suggesting that the protein may be involved in postGolgi traffi cking of membranes ( 202 ). PHR1 is present in outer segments and binds to transducin ␤ ␥ subunits but does not bind to inositol phosphates; however, PI lipids were not tested ( 204 ).…”

“…The best examples are Akt isoforms ( 52,135 ), IRS-1, IRS-2 ( 52, 68, 69 ), Grb14 ( 157 ), Evictin-1 ( 202 ), PHR1 ( p leckstrin h omology domain r etinal protein) ( 203,204 ), and recently identifi ed Akt dephosphorylating enzymes PHLPP (PH domain and leucine rich repeat protein phosphatases) and PHLPPL (PH domain and leucine rich repeat protein phosphatase-like) ( 205 ). Deletion of two PI-binding proteins, Akt2 ( 135 ) and IRS-2 ( 69 ), in the retina results in photoreceptor degeneration.…”

PHR1, an integral membrane protein of the inner ear sensory cells, directly interacts with myosin 1c and myosin VIIa

“…Immunohistochemistry and chemical extraction studies on the photoreceptor outer segment have shown that PHR1 is an integral membrane protein (Xu et al, 1999). PHR1 contains an N-terminal pleckstrin homology domain (Krappa et al, 1999;Xu et al, 1999). Pleckstrin homology (PH) domains are 100-to 120-amino acid modules best known for their ability to bind to phosphoinositides (Lemmon et al, 2002).…”

“…We identified 71 clones by histidine nutritional selection and β-galactosidase (β-gal) activity. The inserts from the isolated clones were sequenced, leading to the identification of four overlapping clones that encode the C-terminal region of a protein named PHR1 (Krappa et al, 1999;Xu et al, 1999) (Fig. 1B).…”