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Biophys J, October 2002, p. 2280-2291, Vol. 83, No. 4

Calcium-Dependent Conformational Rearrangements and Protein Stability in Chicken Annexin A5

Javier Turnay,* Nieves Olmo,* María Gasset,dagger Ibón Iloro,Dagger José Luis R. Arrondo,Dagger and M. Antonia Lizarbe*

 *Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain;  dagger Instituto Rocasolano de Química-Física, CSIC, 28006 Madrid, Spain; and  Dagger Unidad de Biofísica (Centro Mixto CSIC-UPV) y Departamento de Bioquímica, Universidad del País Vasco, Apdo. 644, 48080 Bilbao, Spain

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 (~8°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 (~1650 cm-1) and another, at a lower wavenumber (~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°C), this effect being higher for human annexin; and an increase in canonical alpha -helix percentage by a rearrangement of nonperiodical structure or 310 helices together with a variation in helix-helix interactions, as shown by amide I curve-fitting and 2D-IR.

Biophys J, October 2002, p. 2280-2291, Vol. 83, No. 4
© 2002 by the Biophysical Society   0006-3495/02/10/2280/12  $2.00


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