title: Engineering, biophysical characterisation and binding properties of a soluble mutant form of annexin A2 domain IV that adopts a partially folded conformation.
abstract: The four approximately 75-residue domains (repeats) that constitute the annexin core structure all possess an identical five-alpha-helix bundle topology, but the physico-chemical properties of the isolated domains are different. Domain IV of the annexins has previously been expressed only as inclusion bodies, resistant to solubilisation. Analysis of the conserved, exposed hydrophobic residues of the four annexin domains reveals that domain IV contains the largest number of hydrophobic residues involved in interfacial contacts with the other domains. We designed five constructs of domain IV of annexin A2 in which several interfacial hydrophobic residues were substituted by hydrophilic residues. The mutant domain, in which all fully exposed hydrophobic interfacial residues were substituted, was isolated as a soluble protein. Circular dichroism measurements indicate that it harbours a high content of alpha-helical secondary structure and some tertiary structure. The CD-monitored (lambda=222 nm) thermal melting profile suggests a weak cooperative transition. Nuclear magnetic resonance (1H-15N) correlation spectroscopy reveals heterogeneous line broadening and an intermediate spectral dispersion. These properties are indicative of a partially folded protein in which some residues are in a fairly structured conformation, whereas others are in an unfolded state. This conclusion is corroborated by 1-anilinonaphthalene-8-sulfonate fluorescence (ANS) analyses. Surface plasmon resonance measurements also indicate that this domain binds heparin, a known ligand of domain IV in the full-length annexin A2, although with lower affinity.
authors.affiliation: Department of Biomedicine, University of Bergen, N-5009 Bergen, Norway.
authors.forename: Ingvild
authors.initials: I
authors.lastname: Aukrust
authors.forename: Lasse
authors.initials: L
authors.lastname: Evensen
authors.forename: Hanne
authors.initials: H
authors.lastname: Hollås
authors.forename: Frode
authors.initials: F
authors.lastname: Berven
authors.forename: R Andrew
authors.initials: RA
authors.lastname: Atkinson
authors.forename: Gilles
authors.initials: G
authors.lastname: Travé
authors.forename: Torgeir
authors.initials: T
authors.lastname: Flatmark
authors.forename: Anni
authors.initials: A
authors.lastname: Vedeler
mesh_terms: D000595:Amino Acid Sequence; D017306:Annexin A2 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D012995:Solubility
chemical_list: C472822:ANXA2 protein, human; D017306:Annexin A2; D008024:Ligands; D011993:Recombinant Fusion Proteins