title: Calcium-dependent conformational rearrangements and protein stability in chicken annexin A5.
abstract: The conformational rearrangements that take place after calcium binding in chicken annexin A5 and a mutant lacking residues 3-10 were analyzed, in parallel with human annexin A5, by circular dichroism (CD), infrared spectroscopy (IR), and differential scanning calorimetry. Human and chicken annexins present a slightly different shape in the far-UV CD and IR spectra, but the main secondary-structure features are quite similar (70-80% alpha-helix). However, thermal stability of human annexin is significantly lower than its chicken counterpart (approximately 8 degrees C) and equivalent to the chicken N-terminally truncated form. The N-terminal extension contributes greatly to stabilize the overall annexin A5 structure. Infrared spectroscopy reveals the presence of two populations of alpha-helical structures, the canonical alpha-helices (approximately 1650 cm(-1)) and another, at a lower wavenumber (approximately 1634 cm(-1)), probably arising from helix-helix interactions or solvated alpha-helices. Saturation with calcium induces: alterations in the environment of the unique tryptophan residue of the recombinant proteins, as detected by near-UV CD spectroscopy; more compact tertiary structures that could account for the higher thermal stabilities (8 to 12 degrees C), this effect being higher for human annexin; and an increase in canonical alpha-helix percentage by a rearrangement of nonperiodical structure or 3(10) helices together with a variation in helix-helix interactions, as shown by amide I curve-fitting and 2D-IR.
mesh_terms: D000818:Animals; D017302:Annexins / Q000737:chemistry*; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000378:metabolism*; D002152:Calorimetry, Differential Scanning; D002645:Chickens; D002942:Circular Dichroism; D018076:DNA, Complementary / Q000378:metabolism; D008958:Models, Molecular; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins; D013055:Spectrophotometry, Infrared; D013696:Temperature; D013816:Thermodynamics
chemical_list: D017302:Annexins; D018076:DNA, Complementary; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D002118:Calcium