title: Collagen-binding matrix proteins from elastomeric extraorganismic byssal fibers.
abstract: The byssal threads of marine mussels represent a peculiar case of extraorganismic extracellular material. The threads consist of fibrous chimeric collagens such as preCol-P (with collagenous, elastin-like and histidine-rich domains) embedded in a microfibrillar matrix. We report here on the extraction, purification, and characterization of water-soluble proximal thread matrix protein 1 (PTMP1), which is preferentially located in the proximal portion of each byssal thread and decreases in a proximal to distal direction. PTMP1 has a mass of about 50 kDa as determined by matrix-assisted laser desorption-ionization with time-of-flight (MALDI-TOF) mass spectrometry. Glycine is the most common residue at 12.2 mol %, followed by asparagine/aspartic acid and glutamine/glutamic acid at 11.4 and 9.9 mol %, respectively. Glycosylation has been detected by Western blotting with biotinylated concanavalin A and neutral sugar analysis. With degenerate primers designed from the N-terminal sequence and an additional internal peptide derived by Lys-C endopeptidase digestion, a complete cDNA sequence for this protein was obtained by polymerase chain reaction (PCR) amplification of a Mytilus edulis foot cDNA library. Two variants with minor sequence differences limited to the N-terminus were found. The cDNA-deduced protein sequence reveals two symmetric internal repeats that together account for >85% of the protein. Sequence and epitope similarity of PTMP1 to the A domains of von Willebrand factor and integrin alpha(1)I suggest a capacity for collagen binding. Enzyme-linked immunosorbent assay (ELISA)-based measurement of PTMP1 binding to immobilized type I collagen shows high affinity (apparent K(D) = 0.25 microM), but the binding exhibits no dependence on metals. Using primers designed from M. edulis, we also found a PTMP1-like cDNA in a related species, M. galloprovincialis, with a deduced protein sequence having 97% identity with one M. edulis variant and 99% identity with the other. The corresponding cDNA sequences have 94% and 96% identity, respectively.
authors.affiliation: MCDB Department and Marine Science Institute, University of California at Santa Barbara, Santa Barbara, California 93106, USA.
authors.forename: Chengjun
authors.initials: C
authors.lastname: Sun
authors.forename: Jared M
authors.initials: JM
authors.lastname: Lucas
authors.forename: J Herbert
authors.initials: JH
authors.lastname: Waite
mesh_terms: D000818:Animals; D001672:Biocompatible Materials / Q000737:chemistry* / Q000302:isolation & purification; D049872:Bivalvia; D002241:Carbohydrates / Q000032:analysis; D003094:Collagen / Q000737:chemistry*; D020724:Elastomers; D016326:Extracellular Matrix Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification*; D006023:Glycoproteins / Q000737:chemistry / Q000302:isolation & purification; D007106:Immune Sera; D007118:Immunoassay; D008297:Male; D008969:Molecular Sequence Data; D011485:Protein Binding; D011817:Rabbits; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D020539:Sequence Analysis, Protein; D014841:von Willebrand Factor / Q000737:chemistry
chemical_list: D001672:Biocompatible Materials; D002241:Carbohydrates; D020724:Elastomers; D016326:Extracellular Matrix Proteins; D006023:Glycoproteins; D007106:Immune Sera; D014841:von Willebrand Factor; D003094:Collagen