TAILIEUCHUNG - Báo cáo khoa học: The complex of the insect LDL receptor homolog, lipophorin receptor, LpR, and its lipoprotein ligand does not dissociate under endosomal conditions

The insect low-density lipoprotein (LDL) receptor (LDLR) homolog, lipo-phorin receptor (LpR), mediates endocytic uptake of the single insect lipo-protein, high-density lipophorin (HDLp), which is structurally related to LDL. However, in contrast to the fate of LDL, which is endocytosed by LDLR, we previously demonstrated that after endocytosis, HDLp is sorted to the endocytic recycling compartment and recycled for resecretion in a transferrin-like manner. | ỊFEBS Journal The complex of the insect LDL receptor homolog lipophorin receptor LpR and its lipoprotein ligand does not dissociate under endosomal conditions Sigrid D. Roosendaal1 Jana Kerver1 Maria Schipper2 Kees W. Rodenburg1 and Dick J. Van der Horst1 1 Division of Endocrinology and Metabolism Department of Biology Institute of Biomembranes Utrecht University the Netherlands 2 Department of Biology Centre for Biostatistics Utrecht University the Netherlands Keywords acidic pH apolipophorin calcium endocytic recycling compartment ligand recycling Correspondence K. W. Rodenburg Division of Endocrinology and Metabolism Department of Biology and Institute of Biomembranes Utrecht University NL-CH Utrecht the Netherlands Fax 31 30 253 2837 Tel 31 30 253 9331 E-mail Received 26 December 2007 revised 10 February 2008 accepted 12 February 2008 doi The insect low-density lipoprotein LDL receptor LDLR homolog lipo-phorin receptor LpR mediates endocytic uptake of the single insect lipoprotein high-density lipophorin HDLp which is structurally related to LDL. However in contrast to the fate of LDL which is endocytosed by LDLR we previously demonstrated that after endocytosis HDLp is sorted to the endocytic recycling compartment and recycled for resecretion in a transferrin-like manner. This means that the integrity of the complex between HDLp and LpR is retained under endosomal conditions. Therefore in this study the ligand-binding and ligand-dissociation capacities of LpR were investigated by employing a new flow cytometric assay using LDLR as a control. At pH the LpR-HDLp complex remained stable whereas that of LDLR and LDL dissociated. Hybrid HDLp-binding receptors containing either the b-propeller or both the b-propeller and the hinge region of LDLR appeared to be unable to release ligand at endosomal pH revealing that the stability of the complex is imparted by the ligandbinding domain of LpR. The LpR-HDLp .

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