Origins of a cyanobacterial 6-phosphogluconate dehydrogenase in plastid-lacking eukaryotes

BackgroundPlastids have inherited their own genomes from a single cyanobacterial ancestor, but the majority of cyanobacterial genes, once retained in the ancestral plastid genome, have been lost or transferred into the eukaryotic host nuclear genome via endosymbiotic gene transfer. Although previous studies showed that cyanobacterial gnd genes, which encode 6-phosphogluconate dehydrogenase, are present in several plastid-lacking protists as well as primary and secondary plastid-containing phototrophic eukaryotes, the evolutionary paths of these genes remain elusive. ResultsHere we show an extended phylogenetic analysis including novel gnd gene sequences from Excavata and Glaucophyta. Our analysis demonstrated the patchy distribution of the excavate genes in the gnd gene phylogeny. The Diplonema gene was related to cytosol-type genes in red algae and Opisthokonta, while heterolobosean genes occupied basal phylogenetic positions with plastid-type red algal genes within the monophyletic eukaryotic group that is sister to cyanobacterial genes. Statistical tests based on exhaustive maximum likelihood analyses strongly rejected that heterolobosean gnd genes were derived from a secondary plastid of green lineage. In addition, the cyanobacterial gnd genes from phototrophic and phagotrophic species in Euglenida were robustly monophyletic with Stramenopiles, and this monophyletic clade was moderately separated from those of red algae. These data suggest that these secondary phototrophic groups might have acquired the cyanobacterial genes independently of secondary endosymbioses. ConclusionWe propose an evolutionary scenario in which plastid-lacking Excavata acquired cyanobacterial gnd genes via eukaryote-to-eukaryote lateral gene transfer or primary endosymbiotic gene transfer early in eukaryotic evolution, and then lost either their pre-existing or cyanobacterial gene

<Regular article>Opioid Receptor Affinities of Tyrosine ω-Phenylalkyl Esters, Simple Enkephalin Pharmacophore-mimics.

In order to substantiate the hypothesis that the μ-, δ-, or κ-opioid receptor Affinity of opioid peptides can be elicited by an amino-terminus tyrosine residue and the 4th phenylalanine aromatic ring lying in the proper spatial disposition, a series of simple peptide-mimic tyrosine esters, in which tyrosine is linked to aromatic ring separated by a variety of methylene spacers, were prepared and evaluated by in vitro radioligand receptor assay. Compounds having the 6 or 7 methylene spacers were more potent in opioid receptor affinity than those having fewer or more methylene spacers. The N-monomethyl- and N, N-dimethyltyrosine congeners were more potent than the corresponding tyrosine esters. The order of the receptor type selectivity of these compounds was μ>>δ>κ