title: Structural and functional characterization of recombinant mouse annexin A11: influence of calcium binding.
abstract: Annexin A11 is one of the 12 vertebrate subfamilies in the annexin superfamily of calcium/phospholipid-binding proteins, distinguishable by long, non-homologous N-termini rich in proline, glycine and tyrosine residues. As there is negligible structural information concerning this annexin subfamily apart from primary sequence data, we have cloned, expressed and purified recombinant mouse annexin A11 to investigate its structural and functional properties. CD spectroscopy reveals two main secondary-structure contributions, alpha-helix and random coil (approx. 30% each), corresponding mainly to the annexin C-terminal tetrad and the N-terminus respectively. On calcium binding, an increase in alpha-helix and a decrease in random coil are detected. Fluorescence spectroscopy reveals that its only tryptophan residue, located at the N-terminus, is completely exposed to the solvent; calcium binding promotes a change in tertiary structure, which does not affect this tryptophan residue but involves the movement of approximately four tyrosine residues to a more hydrophobic environment. These calcium-induced structural changes produce a significant thermal stabilization, with an increase of approx. 14 degrees C in the melting temperature. Annexin A11 binds to acidic phospholipids and to phosphatidylethanolamine in the presence of calcium; weaker calcium-independent binding to phosphatidylserine, phosphatidic acid and phosphatidylethanolamine was also observed. The calcium-dependent binding to phosphatidylserine is accompanied by an increase in alpha-helix and a decrease in random-coil contents, with translocation of the tryptophan residue towards a more hydrophobic environment. This protein induces vesicle aggregation but requires non-physiological calcium concentrations in vitro. A three-dimensional model, consistent with these data, was generated to conceptualize annexin A11 structure-function relationships.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias Químicas, Universidad Complutense, 28040 Madrid, Spain.
authors.forename: Emilio
authors.initials: E
authors.lastname: Lecona
authors.forename: Javier
authors.initials: J
authors.lastname: Turnay
authors.forename: Nieves
authors.initials: N
authors.lastname: Olmo
authors.forename: Ana
authors.initials: A
authors.lastname: Guzmán-Aránguez
authors.forename: Reginald O
authors.initials: RO
authors.lastname: Morgan
authors.forename: Maria-Pilar
authors.initials: MP
authors.lastname: Fernandez
authors.forename: Ma Antonia
authors.initials: MA
authors.lastname: Lizarbe
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017302:Annexins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002942:Circular Dichroism; D018076:DNA, Complementary / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010743:Phospholipids / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D011994:Recombinant Proteins; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D013696:Temperature; D014364:Tryptophan / Q000737:chemistry; D014443:Tyrosine / Q000378:metabolism
chemical_list: D017302:Annexins; D018076:DNA, Complementary; D010743:Phospholipids; D011994:Recombinant Proteins; D014443:Tyrosine; D014364:Tryptophan; D002118:Calcium