title: Cartilage Acidic Protein 2 a hyperthermostable, high affinity calcium-binding protein.
abstract: Cartilage Acidic Protein 2 (CRTAC2) is a novel protein present from prokaryotes to vertebrates with abundant expression in the teleost fish pituitary gland and an isoform of CRTAC1, a chondrocyte marker in humans. The two proteins are non-integrins containing N-terminal integrin-like Ca(2+)-binding motifs and their structure and function remain to be assigned. Structural studies of recombinant sea bream (sb)CRTAC2 revealed it is composed of 8.8% α-helix, 33.4% β-sheet and 57.8% unordered protein. sbCRTAC2 bound Ca(2+) with high affinity (K(d)=1.46nM) and favourable Gibbs free energy (∆G=-12.4kcal/mol). The stoichiometry for Ca(2+) bound to sbCRTAC2 at saturation indicated six Ca(2+) ligand-binding sites exist per protein molecule. No conformational change in sbCRTAC2 occurred in the presence of Ca(2+). Fluorescence emission revealed that the tertiary structure of the protein is hyperthermostable between 25°C and 95°C and the fully unfolded state is only induced by chemical denaturing (4M GndCl). sbCRTAC has a widespread tissue distribution and is present as high molecular weight aggregates, although strong reducing conditions promote formation of the monomer. sbCRTAC2 promotes epithelial cell outgrowth in vitro suggesting it may share functional homology with mammalian CRTAC1, recently implicated in cell-cell and cell-matrix interactions.
authors.affiliation: Comparative and Molecular Endocrinology Group, CCMAR, CIMAR-Laboratório Associado, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal. lanjos@ualg.pt
authors.forename: Liliana
authors.initials: L
authors.lastname: Anjos
authors.forename: Ana S
authors.initials: AS
authors.lastname: Gomes
authors.forename: Eduardo P
authors.initials: EP
authors.lastname: Melo
authors.forename: Adelino V
authors.initials: AV
authors.lastname: Canário
authors.forename: Deborah M
authors.initials: DM
authors.lastname: Power
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D015153:Blotting, Western; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D002942:Circular Dichroism; D004848:Epithelium / Q000187:drug effects / Q000254:growth & development; D029941:Fish Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D021541:Sea Bream / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D002135:Calcium-Binding Proteins; D029941:Fish Proteins; D011994:Recombinant Proteins; D002118:Calcium