Structural and ligand binding analysis of recombinant blo t 13 allergen from Blomia tropicalis mite, a fatty acid binding protein.

BACKGROUND: We have previously described a cDNA (clone Bt6) encoding a novel allergen from Blomia tropicalis, which showed sequence similarities to the FABP/P2/cellular retinoic acid binding protein/cellular retinol binding protein, a family of cytosolic lipid transport proteins (cLTPs). This work was planned to better characterize this allergen to which the official name Blo t 13 had been assigned.
METHODS: Fluorescence-based lipid ligand binding assays and secondary structure analysis by circular dicroism were carry out using recombinant Blo t 13 (rBlo t 13) protein. Structural predictions and molecular modelling were performed based on the amino acid sequence inferred from the open reading frame of Bt6 cDNA sequence.
RESULTS: rBlot t 13 binds the natural fluorescent fatty acid cis-parinaric acid and oleic acid by competition, but not retinol, retinoic acid, cholesterol, dansylated or anthroxylated fatty acids such as dansyl-DL-aminocaprylic acid and 12-(9-anthroyloxy)-stereate. Circular dichroism analysis indicated that rBlo t 13 comprises 45% beta-sheet and 13% alpha-helix. The amino acid sequence of Blo t 13 modelled well to known crystal structures of cLTPs providing a tertiary structural model comprising ten beta-strands organized into two beta-sheets, and two short alpha-helices.
CONCLUSION: Blo t 13 is a fatty acid-specific member of the beta-rich cLTP family of proteins.