title: Tissue-specific co-expression and in vitro heteropolymer formation of the two small branchiostoma intermediate filament proteins A3 and B2.
abstract: The two small intermediate filament (IF) proteins A3 and B2 of the cephalochordate Amphioxus were investigated. Blot overlays indicated a heterotypic interaction pattern of the recombinant proteins. While the individual proteins formed only aggregates, the stoichiometric mixture formed obligatory heteropolymeric filaments. Mutant proteins with a single cysteine residue in equivalent positions gave rise to filaments that oxidize to the disulfide-linked heterodimer, which can again form IF. Thus the A3/B2 filaments, which are expressed in the intestinal epithelium, are based on a hetero coiled coil. This keratin-like assembly process of A3 plus B2 was unexpected, since previous evolutionary tree calculations performed by two laboratories on the various Amphioxus IF proteins identified keratin I and II orthologs but left the A/B group as a separate branch. We discuss obvious evolutionary aspects of the Amphioxus IF multigene family, including the previously made observation that B1, the closest relative of B2, forms homopolymeric IF in vitro and is, like vertebrate type III proteins, expressed in mesodermally derived tissues.
authors.affiliation: Department of Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, Goettingen, 37077, Germany. akarabil@gwdg.de
authors.forename: Anton
authors.initials: A
authors.lastname: Karabinos
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schünemann
authors.forename: David A D
authors.initials: DA
authors.lastname: Parry
authors.forename: Klaus
authors.initials: K
authors.lastname: Weber
mesh_terms: D000375:Aging / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D001704:Biopolymers / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D002816:Chordata, Nonvertebrate / Q000737:chemistry* / Q000254:growth & development / Q000378:metabolism; D016384:Consensus Sequence; D019281:Dimerization; D004220:Disulfides / Q000378:metabolism; D019143:Evolution, Molecular; D005455:Fluorescent Antibody Technique; D006801:Humans; D007381:Intermediate Filament Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D007633:Keratins / Q000737:chemistry; D007814:Larva / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010802:Phylogeny; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D055672:Static Electricity
chemical_list: D001704:Biopolymers; D004220:Disulfides; D007381:Intermediate Filament Proteins; D007633:Keratins