J Vet Sci.  2002 Dec;3(4):265-272.

Topology of Scavenger Receptor Class B Type I (SR-BI) on Brush Border Membrane

• Han CH
• Lee MH

Abstract

Both hydropathy plot and in vitro translation results predict the topology of SR-BI; the receptor is an integral membrane protein of 509 amino acids, consisting of a short cytoplasmic N-terminus of 9 amino acids followed by a first transmembrane domain of 22 amino acids, the extracellular domain of 408 amino acids, the second transmembrane domain of 22 amino acids, and the cytoplasmic C-terminus of 47 amino acids. The immunoblot of rBBMV in the presence or absence of pAb589 peptide antigen (the C-terminal 22 amino acid residues of SR-BI) confirmed that the bands at apparent molecular weight of 140 and 210 kDa are SR-BI related protein which might be multimeric forms of SR-BI. 125I apo A-I overlay analysis showed that SR-BI can bind to its ligand, apo A-I, only when it is thoroughly matured - glycosylated and dimerized. The antibody which was generated against extracellular domain of SR-BI (pAb230) not only prevented 125I-labeled apo A-I from binding to 140 kDa band but also inhibited the esterified cholesterol uptake of rabbit BBMV with its IC50 value of 40 microgram/ml of IgG. In contrast, the antibody generated against the C-terminal domain of SR-BI (pAb589) did not show any effect either on cholesterol uptake of rabbit BBMV or 125I-labeled apo A-I binding to 140 kDa band. Overall results show that the ligand binding site of SR-BI in rabbit BBMV is located in extracellular domain, and SR-BI is only functional when it is part of dimeric forms which rationalize the previously found cooperative nature of the binding interaction and maybe a fundamental finding towards the so far poorly understood mechanism of SR-BI function.

Keyword

scavenger recept or class B type I; brush border membrane; apolipoprotein A-I

MeSH Terms

Amino Acid Sequence
Animals
Antigens, CD36/*metabolism
Apolipoprotein A-I/metabolism
Binding Sites/physiology
Blotting, Western
Caco-2 Cells
Cholesterol Esters/metabolism
Humans
Intestinal Mucosa/metabolism
Intestine, Small/*metabolism/ultrastructure
Iodine Radioisotopes
Membrane Proteins/*metabolism
Microvilli/metabolism
Molecular Sequence Data
Rabbits
*Receptors, Immunologic
Receptors, Lipoprotein/*metabolism
Receptors, Scavenger
Scavenger Receptors, Class B
Surface Properties