title: Characterization of the matrilin coiled-coil domains reveals seven novel isoforms.
abstract: Matrilins constitute a family of four oligomeric extracellular proteins that are involved in the development and homeostasis of cartilage and bone. To reveal their homo- and heterotypic oligomerization propensities, we analyzed the four human matrilin coiled-coil domains by biochemical and biophysical methods. These studies not only confirmed the homo- and heterotypic oligomerization states reported for the full-length proteins but revealed seven novel matrilin isoforms. Specific heterotrimeric interactions of variable chain stoichiometries were observed between matrilin-1 and matrilin-2, matrilin-1 and matrilin-4, and matrilin-2 and matrilin-4. In addition, matrilin-1 formed two different specific heterotetramers with matrilin-3. Interestingly, a distinct heterotrimer consisting of three different chains was formed between matrilin-1, matrilin-2, and matrilin-4. No interactions, however, were observed between matrilin-2 and matrilin-3 or between matrilin-3 and matrilin-4. Both homo- and heterotypic oligomers folded into parallel disulfide-linked structures, although coiled-coil formation was not dependent on disulfide bridge formation. Our results indicate that the heterotypic preferences seen for the matrilin coiled-coil domains are the result of the packing of the hydrophobic core rather than ionic interactions. Mass spectrometry revealed that the concentrations of the individual chains statistically determined the stoichiometry of the heteromers, suggesting that formation of the different matrillin chain combinations is controlled by expression levels.
authors.affiliation: Department of Biophysical Chemistry, Biozentrum, University of Basel, CH-4056 Basel, Switzerland.
authors.forename: Sabine
authors.initials: S
authors.lastname: Frank
authors.forename: Therese
authors.initials: T
authors.lastname: Schulthess
authors.forename: Ruth
authors.initials: R
authors.lastname: Landwehr
authors.forename: Ariel
authors.initials: A
authors.lastname: Lustig
authors.forename: Thierry
authors.initials: T
authors.lastname: Mini
authors.forename: Paul
authors.initials: P
authors.lastname: Jenö
authors.forename: Jürgen
authors.initials: J
authors.lastname: Engel
authors.forename: Richard A
authors.initials: RA
authors.lastname: Kammerer
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D004591:Electrophoresis, Polyacrylamide Gel; D016326:Extracellular Matrix Proteins / Q000737:chemistry*; D006023:Glycoproteins / Q000737:chemistry*; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D020033:Protein Isoforms / Q000737:chemistry*; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D016326:Extracellular Matrix Proteins; D006023:Glycoproteins; D020033:Protein Isoforms; D011994:Recombinant Proteins