Abstract
Lipocalins represent the most important protein family of the mammalian respiratory allergens. Four of the seven named dog allergens are lipocalins: Can f 1, Can f 2, Can f 4, and Can f 6. We present the structure of Can f 6 along with data on the biophysical and biological activity of this protein in comparison with other animal lipocalins. The Can f 6 structure displays the classic lipocalin calyx-shaped ligand binding cavity within a central β-barrel similar to other lipocalins. Despite low sequence identity between the different dog lipocalin proteins, there is a high degree of structural similarity. On the other hand, Can f 6 has a similar primary sequence to cat, horse, mouse lipocalins as well as a structure that may underlie their cross reactivity. Interestingly, the entrance to the ligand binding pocket is capped by a His instead of the usually seen Tyr that may help select its natural ligand binding partner. Our highly pure recombinant Can f 6 is able to bind to human IgE (hIgE) demonstrating biological antigenicity.
Highlights
Analyses over the last 2 decades have revealed that most allergens can be grouped into a few families of proteins[1]
Unique regions in the capping region and shape of the ligand binding pocket may play a role in ligand recognition, binding, and ultimate function in vivo. We describe both unique and common features of Can f 6 and similar lipocalins that underlie their allergenicity
The cDNA sequence based on Can f 6[11] was synthetically created from KEGG cfa: 481674 encompassing the entire protein but without the signal sequence and cloned with a C-terminal His6-tag
Summary
Analyses over the last 2 decades have revealed that most allergens can be grouped into a few families of proteins[1]. One such family is made up of lipocalins. These are amongst the most important inhalant animal allergens. Lipocalins are small proteins, usually composed of less than 200 amino acids. In spite of their shared ability to act as allergens they have limited sequence homology with each other, even as low as 20%.
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