title: cDNA sequences of two arylphorin subunits of an insect biliprotein: phylogenetic differences and gene duplications during evolution of hexamerins-implications for hexamer formation.
abstract: Arylphorins represent a conserved class of hexameric ∼500 kDa insect hemolymph glycoproteins, rich in aromatic amino acids, which are produced in large quantities at the larval stage as reserves for metamorphosis and egg development. The recently isolated arylphorin from the moth Cerura vinula is unique in being complexed to a novel farnesylated bilin. Protein sequencing suggested the presence of two different ∼85 kDa subunits. Here, we report the complete coding sequences of two cDNAs encoding two arylphorins subunits with 67% identity and calculated physicochemical characteristics in agreement with the isolated holoprotein. Our phylogenetic analyses of the hexamerins revealed monophyletic origins not only for each of the arylphorins and methionine-rich proteins (H-type and M-type), the two major classes of hexamerins, but also for the minor groups of arylphorin-like and riboflavin-binding hexamerins. We named the latter proteins X-type (mixed type) hexamerins because they share sequence features with both major groups, and they show unique deletions and insertions at conserved sites located on the protein surface. We present a phylogenetic tree of lepidopteran hexamerins, which is in agreement with actual systematics. Overall, duplications of hexamerin genes occurred independently in several lepidopteran lineages. We also analyzed the hexamerin sequences for key parameters, which characterize each type of hexamerins. Based on the crystal structure of the homomeric arylphorin from Antheraea pernyi, we present a model for the heteromeric Cerura protein focusing on the role of N-glycan structures in stabilizing the hexamer structure.
authors.affiliation: Institut für Zoologie, Johannes Gutenberg-Universität, Mainz, Germany.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Lieb
authors.affiliation: Institut für Zoologie, Johannes Gutenberg-Universität, Mainz, Germany.
authors.forename: Bettina
authors.initials: B
authors.lastname: Ebner
authors.affiliation: Institute of General Zoology and Endocrinology, Ulm University, Ulm, Germany.
authors.forename: Hartmut
authors.initials: H
authors.lastname: Kayser
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics*; D020440:Gene Duplication; D005786:Gene Expression Regulation / Q000502:physiology*; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D009036:Moths / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D021122:Protein Subunits; D013045:Species Specificity
chemical_list: D018076:DNA, Complementary; D019476:Insect Proteins; D021122:Protein Subunits; C041137:storage proteins, Insecta