Proteome and transcriptional analysis of ethanol-grown Sulfolobus solfataricus P2 reveals ADH2, a potential alcohol dehydrogenase

10.1021/pr070232yJournal of Proteome Research6103985-3994JPRO

Cartilage Acidic Protein 2 a hyperthermostable, high affinity calcium-binding protein

Cartilage Acidic Protein 2 (CRTAC2) is a novel protein present fromprokaryotes to vertebrateswith abundant expression in the teleost fish pituitary gland and an isoformof CRTAC1, a chondrocyte marker in humans. The two proteins are non-integrins containingN-terminal integrin-like Ca2+-bindingmotifs 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 Ca2+ with high affinity (Kd= 1.46 nM) and favourable Gibbs free energy (ΔG=−12.4 kcal/mol). The stoichiometry for Ca2+ bound to sbCRTAC2 at saturation indicated six Ca2+ ligand-binding sites exist per protein molecule. No conformational change in sbCRTAC2 occurred in the presence of Ca2+. 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 (4 MGndCl). sbCRTAC has awidespread tissue distribution and is present as highmolecular 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