Session topic


Title: Structural and functional characterization of Scavenger receptor B1
ID: PS 22
Type: Poster session
Talk time: 3 + 2 min
Session: Poster session 1
Receptors and entry

Speaker: Giacomo Castoro (Hannover/DE)

Abstract - Text

Abstract text (incl. references and figure legends)

Scavenger receptor class B type 1 (SR-B1), a member of the CD36 superfamily, is a 509 amino acid long multi-ligand membrane receptor. It has an N- and C-terminal transmembrane domain framing a large extracellular domain of approximately 408 residues carrying 10 N-linked glycosylation sites. SR-B1 is involved in the delivery of cholesterol esters (CE) to the liver and steroidogenic tissues and has been described to oligomerize into hydrophobic channels to exert this function. Its activity decreases plasma CE levels and thereby reduces the risk of cardiovascular disease making it an attractive target to modulate CE levels via specific activating small molecules.

In addition, SR-B1 plays a crucial role in cell entry of hepatitis C virus (HCV). Two distinct mechanisms have been proposed how SR-B1 promotes infection of HCV. SR-B1 can either directly interact with the hypervariable region 1 of the major HCV glycoprotein E2, or it can form a complex with high density lipoproteins (HDL) associated with the HCV lipoviral particles. However, the precise mechanism-of-action of SR-B1 in HCV entry remains elusive to date.

Our goal is to gain insights into the role of SR-B1 in both HCV entry and lipid uptake. Therefore, we have expressed and purified important amounts of a soluble SR-B1 ectodomain (SR-B1e) in insect cells. Characterization of this purified ectodomain revealed an equilibrium between monomeric and dimeric SR-B1e, in line with results observed for soluble forms of the related scavenger protein CD36. Unexpectedly, in low pH buffers we observed a tendency to form a more stable monomeric SR-B1e. Using this mixture we immunized mice to generate an SR-B1-specific single chain variable fragment (scFv) library. The use of specific antibody fragments will enable us to functionally characterize ligand binding of SR-B1 and ultimately represent invaluable tools for structure determination of the SR-B1 ectodomain using X-ray crystallography.