Binding of retinol

Figure B3.6.11 The binding of retinol to p-lactoglobutin that has been denatured by exposure to high pressure. The sample contaiining 270 pM p-lactoglobulin was pressurized to 400 MPa for 15 min. After release of pressure, retinol in ethanol was added and fluorescence was measured as a function of time. Parameters final protein concentration 8.5 pM in 20 mM phosphate buffer . ex = 330 nm k9m = 470 nm. Circles, native p-lactoglobulin triangles, pressurized p-lactoglobulin. Reprinted from Ikeuchi et al. (2001) with permission from the American Chemical Society.

Tschanz CL and Noy N (1997) Binding of retinol in both retinoid-binding sites of interphotoreceptor retinoid-binding protein (IRBP) is stabilized mainly by hydrophobic mtetActiom,. Journal of Biological Chemistry 272,30201-7. 

Fig. 13.11. Binding of retinol to the active site of retinol binding protein (IRBP, stereo-diagram). The ligand is completely encapsulated in the protein with the y -ionone ring in the center and the unsaturated isoprene chromophore stretching to the solvent surface along the main axis of the fi barrel packing motif in this protein...

Figure 4.23 Schematic representation of the tertiary structure of bovine -lactoglobulin. showing the binding of retinol arrows indicate antiparallel -sheet structures (from Papiz et...

At variance with the relatively fast binding of retinol to apo-CRBP, which takes place in less than 1 mm, the kinetics of RME binding to apo-CRBP is rather slow. Therefore, several minutes of incubation after the addition of RME to apo-CRBP are required before absorbance and fluorescence spectra of the CRBP-RME complex are run. 

Apply the mixture to a Lipidex-1000 resin (column bed volume -2 mL) and elute with three column volumes of 10 mM Tris-HCl, pH 7 5 Collect the eluant and freeze-dry (Excess retinol will be retained by the resin.) Dissolve the protein in a suitable volume of PBS and measure the absorbance spectrum to confirm the binding of retinol to the protein... 

Binding of Retinol to the Hydrophobic Retinoid-Binding Site ofIRBP... 

Binding of Retinol at Both Retinoid-Binding Sites of IRBP... 

Fig. 2. Cartoon model of the RBP-TTR complex. TTR is shown as a tetramer containing a central channel that is the site of thyroxine (T4) binding. The locations of the different binding sites suggest the known relations between the several interactions RBP and T4 bind at independent sites on TTR, whereas the binding of retinol to RBP is stabilized by formation of the protein-protein complex. (Reproduced with permission from Smith and Goodman, 1979.)...

These studies with retinoids have provided some information about the structural requirements of the retinol binding site on RBP. No information is, however, available about the amino acid residues in RBP that are involved in the binding site. Acetylation of lysine residues of RBP did not affect its binding of retinol (Heller and Horwitz, 1975). Modification of one of eight tyrosine residues and two of four tryptophan residues of RBP also had no effect on the retinol-RBP interaction (Heller and Horwitz, 1975 Horwitz and Heller, 1974b). The binding site was, however, disrupted by reduction and alkylation of disulfide bonds (Raz et al., 1970). 

A requirement for binding to CRBP appears to be a free alcohol in the C-15 position (Ong and Chytil, 1975b). Retinyl acetate or retinyl palmitate (A4) do not compete for the binding of retinol to partially purified CRBP. In unfractionated cytosols, however, an excess of retinyl acetate or palmitate competed... 

Vitamin A is essential for epidermal proliferation and reepithelialisation binding of retinol to cell surface receptors. It is also important in the inflammatory phase of the chronic wound healing process, which is one of the main reasons for delayed healing. Vitamin A is also related with collagen synthesis and infection. Vitamin B promotes cell proliferation, which helps healthy skin and muscle tone, and also enhances immune and nervous system function. 

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