Low density lipoprotein receptor-related protein 1 (alpha-2-macroglobulin receptor), also known as LRP1 or CD91, is a protein forming a receptor found in the plasma membrane of human cells involved in receptor-mediated endocytosis.Neurons require cholesterol to function. Cholesterol is imported into the neuron by the apolipoprotein apoE4 via LRP1 receptors on the cell surface. It is thought that a causal factor in Alzheimer's is the malfunction of this process which damages neurons by starving them of cholesterol.The protein showed strong calcium binding. Kristensen et al. (1990) and Strickland et al. (1990) demonstrated that LRP is identical to the alpha-2-macroglobulin (A2M) receptor (A2MR). Like the mannose-6-phosphate receptor, the A2MR/LRP molecule is probably bifunctional.