MCAT Style Quiz Question 12.1

A 10-year-old female presents with chest pain and xanthomas over her elbows and knees. Her father died of a heart attack at age 35. Her mother has high cholesterol. Her physician suspects heterozygous familial hypercholesterolemia in the parents with homozygous disease in the daughter. This disease results from mutations in the receptor for low-density lipoprotein (LDL) or the ligand portion of its apoprotein coat. Which ONE of the following apoproteins might be mutated?