Disease relevance of RBP4

• Several mutants of RBP were generated and produced in Escherichia coli, and their Zn(II)-binding properties were investigated in equilibrium dialysis experiments [1].
• Through use of bpRBP antiserum, immunoreactive RBP was detected in uterine flushings collected from cows in the late luteal phase of the estrous cycle and early pregnancy by Western blotting, and in medium conditioned by uterine explants prepared at Days 13-29 of pregnancy by immunoprecipitation [2].

High impact information on RBP4

• The three-dimensional structures of complexes between bovine plasma retinol-binding protein (RBP) and three retinol analogs with different end groups (fenretinide, all-trans retinoic acid, and axerophthene) have been determined to 1.8-1.9-A resolution [3].
• While confirming that an intact hydroxyl end group is not an absolute requirement for a correct retinoid binding to RBP, this study has shown the occurrence of conformational changes, although limited, in the rather flexible loop region at the entrance of the beta-barrel upon fenretinide and retinoic acid binding [3].
• However, the binding of the retinoid to RBP abolishes or greatly reduces the affinity of RBP for transthyretin [4].
• In retinal pigment epithelium the RBP receptor appears to be an oligomeric protein complex, and we have previously identified a 63-kDa membrane protein as part of this receptor [5].
• The three-dimensional structure of bovine plasma retinol-binding protein (RBP) complexed with N-ethyl retinamide has been determined at 1.9-A resolution [4].

Biological context of RBP4

• The RBP cDNA clone, designated bcRBP-700, is 732 bp in length and codes for a protein whose predicted amino acid sequence is identical to that of bovine plasma RBP [6].
• A cDNA clone encoding retinol-binding protein (RBP) was isolated from a bovine conceptus cDNA library by use of an antiserum specific for bovine conceptus RBP (bcRBP) [6].
• Finally, we present experimental evidence that the binding sites of RBP, BLG, and OBP are in different regions of the molecules [7].
• In contrast to the observation on lipocalins as retinol binding protein (RBP), major urinary protein (MUP) or bovine odorant binding protein (bOBP), no naturally occurring ligand was found in the beta-barrel cavity of pOBP [8].
• In pigs, RBP gene expression was low to undetectable at Days 0, 5, and 10 of the estrous cycle and Day 10 of pregnancy [9].

Anatomical context of RBP4

• In addition, RBP mRNA was detected in cotyledons, the sites of chorionic attachment to the uterine endometrium and physiological exchange between the embryo and its mother [6].
• RBP mRNA was localized in epithelial cells lining the chorion, allantois, and amnion at Day 45 of pregnancy [6].
• Expression of RBP in expanding conceptuses, developing extraembryonic membranes, and sites of fetal-maternal attachment suggests that the extraembryonic membranes regulate retinol transport and availability within the conceptus [6].
• Strong immunostaining for RBP and hybridization signals for RBP mRNA were observed in trophectoderm of tubular but not spherical Day 13 blastocysts [6].
• We have used x-ray diffraction techniques on single crystals of human and bovine RBP, bovine milk BLG, and bovine nasal mucosa OBP to investigate this problem [7].

Associations of RBP4 with chemical compounds

• The loops that surround the opening of the beta-barrel are also particularly conserved, in contrast with the presence of several substitutions in parts of the RBP molecule opposite the opening of the calyx that binds retinol [10].
• For this purpose, we have developed a cell-free system composed of plasma membrane-enriched fractions from bovine retinal pigment epithelium which selectively incorporates exogenous vitamin A when presented as a retinol-RBP complex [11].
• This behavior further supports the hypothesis that the area of the entrance of the beta-barrel, which includes the ethyl group of the retinoid bound to RBP, is involved in the interaction with transthyretin [4].
• Retinol, a metabolic precursor of retinal and retinoic acid, is transported in plasma by the plasma retinol-binding protein (RBP) [5].
• In fact, the replacement of the retinol hydroxyl group and quite small structural changes in the above region of the RBP molecule drastically affect the protein-protein recognition [4].

Analytical, diagnostic and therapeutic context of RBP4

• The size of the RBP mRNA transcript in bovine chorioallantois was approximately 1.4 kb as determined by Northern blot analysis [6].
• The bovine plasma retinol-binding protein. Amino acid sequence, interaction with transthyretin, crystallization and preliminary X-ray data [12].
• Placental RBP was immunoprecipitated from radiolabeled allantois and chorion culture medium and was detected in allantoic membrane culture medium and allantoic fluid by Western blotting [13].
• Amino-terminal sequence analysis of 3B3 isolated from allantoic fluid on the first 43 amino acids showed that 3B3 had 93% and 91% homology with rabbit and human plasma retinol-binding protein (RBP), respectively [13].
• Thus it was possible to use the grafted metal-binding site for the efficient purification of the engineered, bifunctional RBP via immobilized metal affinity chromatography from the bacterial protein extract [1].

References