The bovine plasma retinol‐binding protein

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Abstract
1 The primary structure of bovine plasma retinol-binding protein (RBP) has been determined and found to be more than 90% identical to human and rabbit RBPs, and more than 80% identical to rat RBP. Main changes in amino acid sequence are observed in two regions on the surface of the protein molecule (residues 138–148 and 169–183). 2 The interactions of bovine RBP with bovine and human transthyretins were investigated using the technique of fluorescence polarization. Bovine RBP was able to form high affinity complexes (K′d= 0.34 ± 0.02 μM) with both bovine and human transthyretins, displaying a stoichiometry of approximately 2 molecules RBP/molecule transthyretin in both cases. The sites that participate in protein-protein interactions are thus very similar, and this tends to exclude the involvement of the superficial regions more significantly substituted in mammalian RBPs (residues 138–151 and 167–183) in the protein–protein recognition. 3 Bovine RBP has been crystallized (space group P212121, with a= 4.61 nm, b= 4.91 nm, c= 7.61 nm) and the crystals are suitable for high-resolution X-ray diffraction studies.