A Structurally Deviant Member of the Euplotes raikovi Pheromone Family: Er‐23

Abstract

Pheromones of Euplotes raikovi form a homologous family of proteins with 37- to 40-amino acid residues, including six cysteines that form three strictly conserved disulfide bridges. The determination of the primary structure of the pheromone Er-23, which was isolated from cells derived from natural populations of E. raikovi that secrete the other known pheromones, has now revealed a novel structure type. The polypeptide chain of this pheromone contains 51 residues, 10 of which are cysteines presumably involved in the formation of five disulfide bridges, and lacks a carboxyl-terminal tail following the last cysteine of the sequence. The elongation of the Er-23 molecule is presumed to result from multiple events of gene duplication starting from an ancestral motif Xxx(2-4)-Cys-Xxx(5-7)-Cys.

Characterization of the pheromone gene family of an Antarctic and Arctic protozoan ciliate, Euplotes nobilii

“…This peculiar organization of the E. nobilii pheromone genes probably reflects a conserved inclusion of intron sequences, whose splicing might have a fundamental role in the mechanism of expression of these genes. This hypothesis receives support in particular from previous functional analysis of E. raikovi pheromone genes [26,27], showing that the primary transcripts of these genes undergo intron splicing (at not canonical sites) to generate membranebound pheromone isoforms that cells use as autocrine pheromone receptors [9]. Its assessment, in addition to being crucial to elucidate the mechanism of expression of the E. nobilii pheromone gene family, may also contribute insightful information on the more general problem of the functional organization of the sub-chromosomic, gene-sized macronuclear genomes of the hypotrich ciliates.…”

“…As is the case in pheromone genes of other species of Euplotes [14,26,27], these functions are presumably correlated with the inclusion of intron sequences the splicing of which results in the expression of new ORF's and the synthesis of new and functionally diversified pheromone isoforms. This possibility is supported by the common conservation in the 5' regions of, (i) multiple ATG start codons, (ii) A + T rich sequences, and (iii) consensus donor GT (5') and acceptor AG (3') splice-site junctions [28,29].…”

Cold-adaptation in Sea-water-borne Signal Proteins: Sequence and NMR Structure of the Pheromone En-6 from the Antarctic Ciliate Euplotes nobilii

“…Amazingly, this basic structural motif is also retained in a structurally deviant member of the Er family, Er-23, which has a polypeptide chain of 51 residues, forms an additional α-helix and contains two additional disulfide bonds. 11,13,17 Because of their close structural homology, Er pheromones can compete with each other in receptor binding reactions, through which they may Abbreviations used: En, pheromone of Euplotes nobilii; Er, pheromone of Euplotes raikovi; NOE, nuclear Overhauser effect; NOESY, NOE spectroscopy. …”

Ciliate pheromone structures and activity: a review

“…Nine distinct amino acid sequences, designated Er-1, Er-2, Er-7, Er-10, Er-11, Er-20, Er-21, Er-22 and Er-23 (where E and r stand for Euplomone and raikovi, respectively, and the numbers classify progressive pheromone characterizations), have been determined for the E. raikovi pheromone family (Raffioni et al 1992;Giuseppe et al 2002;Luporini et al 2005). As is the case for the B. japonicum Gamone 1 and exocytotic proteins in general, these E. raikovi pheromones also appear to be synthesized as pre-pro-pheromones and secreted after two proteolytic cleavages that remove the pre (signal-peptide) and pro segments (Miceli et al 1991).…”