%0 Journal Article
%T Structural and functional characteristics of xenavidin, the first frog avidin from Xenopus tropicalis
%A Juha AE M£¿£¿tt£¿
%A Satu H Helppolainen
%A Vesa P Hyt£¿nen
%A Mark S Johnson
%A Markku S Kulomaa
%A Tomi T Airenne
%A Henri R Nordlund
%J BMC Structural Biology
%D 2009
%I BioMed Central
%R 10.1186/1472-6807-9-63
%X Xenavidin was identified from an EST sequence database for Xenopus tropicalis and produced in insect cells using a baculovirus expression system. The recombinant xenavidin was found to be homotetrameric based on gel filtration analysis. Biacore sensor analysis, fluorescently labelled biotin and radioactive biotin were used to evaluate the biotin-binding properties of xenavidin - it binds biotin with high affinity though less tightly than do chicken avidin and bacterial streptavidin. X-ray crystallography revealed structural conservation around the ligand-binding site, while some of the loop regions have a unique design. The location of structural water molecules at the entrance and/or within the ligand-binding site may have a role in determining the characteristic biotin-binding properties of xenavidin.The novel data reported here provide information about the biochemically and structurally important determinants of biotin binding. This information may facilitate the discovery of novel tools for biotechnology.Avidins are high-affinity biotin-binding proteins found in the eggs of oviparous vertebrates including bird, reptilian and amphibian species [1-5]. In addition to its production in the oviduct and secretion to egg white, avidin is expressed in several other tissues of the chicken during injury and inflammation [6]. Avidins analogous to those found in the earliest diverging tetrapod species have been isolated from a few bacterial species: Streptomyces avidinii (streptavidin; [7,8]) Bradyrhizobium japonicum (bradavidin; [9]) and Rhizobium etli (rhizavidin; [10]).Avidins are homotetrameric proteins, the only known exception being rhizavidin, which is a homodimer [10]. The avidin subunits consist of eight anti-parallel ¦Â-strands, which form a ¦Â-barrel structure that has a biotin-binding pocket at the open end of the barrel. Avidins interact extraordinarily tightly with a water-soluble vitamin, D-biotin (Kd in the range of 10-13 to 10-15 M). This exceptional strengt
%U http://www.biomedcentral.com/1472-6807/9/63