CHOLESTRUCTURE · REGULATION OF CHOLESTEROL HOMEOSTASIS BY THE ARH-MEDIATED ENDOCYTOSIS OF THE LDL RECEPTOR

Hypercholesterolemia, high levels of plasma LDL-cholesterol, is a major risk factor for atherosclerosis and premature coronary heart disease (CHD), a leading cause of death in worldwide. The clearance of LDL from the circulation occurs via endocytosis with the LDL-receptor (LDLR) mainly by liver cells. This hepatic recruitment of the LDL-LDLR complex to the clathrin-coated pits is dependent on the endocytic adaptor protein, autosomal recessive hypercholesterolemia (ARH), which recognizes the NPxY internalization signal on the LDLR cytoplasmic tail. Consequently, naturally occurring mutations in either LDLR or in ARH lead to sever hypercholesterolemia and premature onset of CHD. Therefore, studying the molecular interactions ARH forms at the cell surface to facilitate endocytosis of the LDLR is central to our understanding of cholesterol homeostasis.I recently solved a novel crystal structure of the LDLR-ARH interface at atomic resolution. Surprisingly, the structure reveals that the phosphotyrosine-binding (PTB) domain of ARH recognizes a longer portion of the LDLR tail than previously believed, and that ARH has discrete structural determinants for somewhat promiscuous binding of NPxY containing signals of various flanking specificities.To gain a detailed mechanistic understanding for the unique endoctytic function of ARH, this proposal will investigate (1) The molecular basis for receptor recognition by solving crystal structures of ARH with all the receptor tails it is known to bind