Hello, kitty: could cat allergy be a form of intoxication?

Abstract

Background: The relationship between slow loris (Nycticebus spp.) venom (BGE protein) and the major cat allergen (Fel d 1) from domestic cat (Felis catus) is known for about two decades. Along this time, evidence was accumulated regarding convergences between them, including their almost identical mode of action.

Methods: Large-scale database mining for Fel d 1 and BGE proteins in Felidae and Nycticebus spp., alignment, phylogeny proposition and molecular modelling, associated with directed literature review were assessed.

Results: Fel d 1 sequences for 28 non-domestic felids were identified, along with two additional loris BGE protein sequences. Dimer interfaces are less conserved among sequences, and the chain 1 shows more sequence similarity than chain 2. Post-translational modification similarities are highly probable.

Conclusions: Fel d 1 functions beyond allergy are discussed, considering the great conservation of felid orthologs of this protein. Reasons for toxicity being found only in domestic cats are proposed in the context of domestication. The combination of the literature review, genome-derived sequence data, and comparisons with the venomous primate slow loris may point to domestic cats as potentially poisonous mammals.

Keywords: Allergy; Cat; Domestication; Fel d 1; Loris; Secretoglobin.

Figure 1.. Sequence alignment for felid Fel d 1 and loris BGE protein. (A) Chain 1, (B) chain 2. Characters are colored highlighting differences from majority rule consensus. Structurally relevant positions are highlighted according to the legend box and include Cys-Cys pairs, interface hydrophobic residues, Ca²⁺ binding residues and a glycosylation site.

Figure 2.. Sequence conservation mapped onto Fel d 1 structure. The information from sequence alignments (Figure 1) was used to locate tridimensionally the positions of greater amino acid conservation. Structure based on PDB ID: 2EJN [17]. A scheme indicating the orientation of each dimer in the tetramer (dimer-of-dimers) is also shown.

Figure 3.. Phylogenetic analyses of felid Fel d 1 and loris BGE protein. (A) Chain 1, (B) chain 2. Felid species are colored according to their current grouping [41]. Branch support is shown as aLRT gradient.