Localization of Drosophila retinal degeneration B, a membrane-associated phosphatidylinositol transfer protein

Abstract

Abstract. The Drosophila retinal degeneration B(rdgB) mutation causes abnormal photoreceptor response and light-enhanced retinal degeneration. Immunoblots using polyclonal anti-rdgB serum showed that rdgB is a 160-kD membrane protein. The antiserum localized the rdgB protein in photoreceptors, antennae, and regions of the Drosophila brain, indicating that the rdgB protein functions in many sensory and neuronal cells. In photoreceptors, the protein localized adjacent to the rhabdomeres, in the vicinity of the subrhabdomeric cisternae. The rdgB protein's aminoterminal 281 residues are >40% identical to the rat brain phosphatidylinositol transfer protein (PI-TP). A truncated rdgB protein, which contains only this amino-terminal domain, possesses a phosphatidylinositol transfer activity in vitro. The remaining 773 carboxyl terminal amino acids have additional functional domains. Nitrocellulose overlay experiments reveal that an acidic amino acid domain, adjacent to the PI transfer domain, binds 45Ca+2. Six hydrophobic segments are found in the middle of the putative translation product and likely function as membrane spanning domains. These results suggest that the rdgB protein, unlike the small soluble PI-TPs, is a membrane-associated PI-TP, which may be directly regulated by light-induced changes in intracellular calcium.

Coordinated Lipid Transfer between the Endoplasmic Reticulum and the Golgi Complex Requires the VAP Proteins and Is Essential for Golgi-mediated Transport

“…In rdgB mutants, light activation of phospholipase C hydrolyzes PIP 2 . Because PI cannot be replenished in the rhabdomeres of rdgB mutants, the membrane experiences a decrease in PI or PIP 2 levels, thereby leading to degeneration (Vihtelic et al, 1993). Consistent with this hypothesis, we show here that Nir2 can restore the Golgi morphology of VAP-depleted cells in its PI-transfer activity-dependent manner.…”

“…Early localization studies of rdgB in photoreceptor cells suggest that it is localized to the subrhabdomeric cisternal (SRC) membranes adjacent to the rhabdomeres (Vihtelic et al, 1993;Suzuki and Hirosawa, 1994). The SRC is an extensive network of membranes derived from the rough ER and thought to play a critical role in maintenance of the rhabdomeric membranes (Matsumoto-Suzuki et al, 1989).…”

Phototransduction and retinal degeneration in Drosophila

“…Light-dependent retinal degeneration results from disruption of other proteins that function in the PIP 2 regeneration cycle, including RDGB (PI transfer protein), CDS (CDP-DAG synthase), and dPIS (PI synthase) [28,29,131,132,229]. Overexpression of PLD, which might lead to the generation of higher levels of PIP 2 through conversion of PC to PA, suppresses the retinal degeneration in the rdgB mutant [137].…”

Insect retinal pigments: Spectral characteristics and physiological functions

“…A recent report by Wu et al (1995) reveals that a photoreceptor-specific CDP-DAG synthase, encoded by the cds gene, participates in the crucial cycle of phosphatidylinositol-4,5-bisphosphate activation and resynthesis; together with a DAG kinase, encoded by D. G. Stavenga the rdgA gene (Masai et al, 1992), a phosphatidylinositol transfer protein, encoded by the rdgB gene (Vihtelic et al, 1993) and the norpA product PLC, of course (Fig. 11).…”