Atomic structure of the autosomal recessive hypercholesterolemia phosphotyrosine-binding domain in complex with the...

Area of Science:

• Biochemistry
• Molecular Biology
• Structural Biology

Background:

• Hypercholesterolemia, characterized by high LDL cholesterol, is a primary risk factor for atherosclerosis.
• LDL clearance primarily occurs in the liver via LDL receptor (LDLR)-mediated endocytosis.
• The autosomal recessive hypercholesterolemia (ARH) protein facilitates LDLR internalization by binding its cytoplasmic tail.

Purpose of the Study:

• To determine the molecular basis of the ARH-LDLR interaction by solving their complex structure.
• To elucidate how mutations in ARH or LDLR lead to hypercholesterolemia and atherosclerosis.

Main Methods:

• X-ray crystallography was used to determine the structure of the ARH PTB domain bound to an LDLR tail peptide at 1.37-Å resolution.
• Biophysical measurements were employed to assess the stability of ARH-LDLR complexes and the impact of mutations.

Main Results:

• The crystal structure revealed that ARH binds a longer segment of the LDLR tail (I(-7)xF(-5)xNPxY(0)QK(+2)) than previously known.
• The LDLR tail adopts a unique "Hook"-like conformation, interacting with specific ARH structural features, including an extended hydrogen-bonding platform and hydrophobic pockets.
• The Y(0) residue of the LDLR tail is accommodated in a distinctive hydrophobic pocket within ARH, explaining ARH's ability to bind both FxNPxY(0) and FxNPxF(0) motifs.
• Mutations associated with hypercholesterolemia were shown to destabilize the ARH-LDLR complex.

Conclusions:

• The determined structure provides unprecedented molecular insight into the ARH-LDLR interaction essential for hepatic LDL uptake.
• The unique binding mode and structural complementarity explain the physiological role of ARH in cholesterol homeostasis.
• The findings illuminate the molecular mechanisms underlying LDL internalization defects in patients with hypercholesterolemia due to ARH or LDLR mutations.