Drosophila vision involves a G protein-coupled phospholipase C-mediated signaling pathway that leads to membrane depolarization through activation of Na+ and Ca2+ channels. InaD mutant flies have a M442K point mutation and display a slow recovery of the Ca2+ dependent current. We report that anti-INAD antibodies coimmunoprecipitate TRP, identified by its electrophoretic mobility, cross reactivity with anti-TRP antibody, and absence in a null allele trp mutant. This interaction is abolished by the InaD point mutation in vitro and in vivo. Interaction was localized to the 19 amino acid C-terminus of TRP by overlay assays, and to the PDZ domain of INAD, encompassing the point mutation. Given the impaired electrophysiology of the InaD mutant, this novel interaction suggests that INAD functions as a regulatory subunit of the TRP Ca2+ channel.
Mutations of the Drosophila melanogaster ninaA gene affect phototransduction: ninaA mutant flies have a 10-fold reduction in the levels of rhodopsin in the R1-R6 photoreceptor cells. The ninaA gene was isolated and found to encode a 237-amino-acid protein that has over 40% amino-acid sequence identity with the vertebrate cyclosporin A-binding protein, cyclophilin, a protein that seems to be involved in T-lymphocyte activation. The remarkable evolutionary conservation of cyclophilin in two phylogenetically distant organisms and its involvement in diverse transduction processes suggests that this protein plays an important role in cellular metabolism. Indeed, cyclophilin has recently been shown to be a prolyl cis-trans isomerase that catalyses, in vitro, rate-limiting steps in the folding of a number of proteins. Here, we present evidence for the involvement of cyclophilin-like molecules in a defined cellular process. The availability of mutations in a cyclophilin gene provides a new model system for the study of cyclophilin and cyclosporin action.
A distant relative of catalase that is specialized for metabolism of a fatty acid hydroperoxide was identified. This heme peroxidase occurs in coral a s part of a fusion protein, the other component of which is a lipoxygenase that forms the hydroperoxide substrate. The end product is an unstable epoxide (an allene oxide) that is a potential precursor of prostaglandin-like molecules. These results extend the known chemistry of catalase-like proteins and reveal a distinct type of enzymatic construct involved in the metabolism of polyunsaturated fatty acids.
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