Do clustered beta-propeller domains within the N-terminus of LRP1 play a functional role?
The six beta-propellers located within the N-terminus of low density lipoprotein receptor-related protein 1 (LRP1) are arranged in two clusters that contain two and four beta-propellers, respectively. Working with LRP1 deletion mutants, we found that randomly removing large segments of amino acid sequences did not affect the intracellular trafficking of LRP1 as long as the clustered beta-propeller domains were retained. However, deletion mutants with crippled beta-propeller clusters invariably exhibited retarded exit from the endoplasmic reticulum (ER). To determine potential functions of the clustered beta-propellers, we generated a series of deletion mutants in which the beta-propellers were systematically removed from the C-terminal end of the second cluster. The resulting minireceptors, designated LRPbeta1-6, beta1-5, beta1-4, beta1-3, and beta1-2 containing decreasing numbers of the beta-propellers, were stably expressed in LRP1-null CHO cells. Binding/degradation assays with receptor-associated protein or alpha2-macroglobulin showed that removing one or more beta-propellers had little effect on binding or degradation of these ligands. However, minireceptors containing odd number of beta-propellers (i.e., LRPbeta1-3 and beta1-5) showed prolonged retention within the ER and remained endoglycosidase H-sensitive, whereas minireceptors containing even number of beta-propellers (i.e., LRPbeta1-2, beta1-4 and beta1-6) exited ER at variable rates. Cell surface biotinylation experiments showed that LRPbeta1-3 was absent from the cell surface. Prolonged retention of LRPbeta1-3 within the ER was accompanied by increased association with molecular chaperone Grp78/Bip. These results suggest that the clustered beta-propellers may play a role in folding and intracellular trafficking of LRP1.
Sun
Fengcheng
F
Lipoprotein and Atherosclerosis Research Group, University of Ottawa Heart Institute, Ottawa, Canada K1Y 4W7.
Avramoglu
Rita Kohen
RK
Vassiliou
Gerard
G
Brown
Robert J
RJ
Ko
Kerry W S
KW
McPherson
Ruth
R
Yao
Zemin
Z
D000818:Animals; D016466:CHO Cells; D019556:COS Cells; D006224:Cricetinae; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins / Q000378:metabolism; D008024:Ligands; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000737:chemistry* / Q000502:physiology; D018832:Molecular Chaperones / Q000378:metabolism; D017510:Protein Folding; D021381:Protein Transport
D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D008024:Ligands; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D018832:Molecular Chaperones