One of three major isoforms of apolipoprotein E. In humans, Apo E2 differs from apolipoprotein e3 at one residue 158 where arginine is replaced by cysteine (R158--C). In contrast to Apo E3, Apo E2 displays extremely low binding affinity for LDL receptors (receptors, ldl) which mediate the internalization and catabolism of lipoprotein particles in liver cells. ApoE2 allelic homozygosity is associated with hyperlipoproteinemia type iii.