Apolipoprotein-E degradation in human very low density lipoproteins by plasma protease(s): Chemical and biological consequences

Serine proteases coisolate with human very low density lipoproteins (VLDL) which degrade apolipoprotein E and cause hypertriglyceridemic VLDL to lose the ability to interact with the LDL receptor of human skin fibroblasts. We identified proteolytic fragments of apolipoprotein-E in isolated VLDL which can be produced by the action of thrombin on purified apoE. There are two major thrombin cleavage products: M_r ∼ 22,000 (E-22) and M_r ∼ 12,000 (E-12), the N- and C-terminal fragments, respectively, of apoE. We conclude that the structural integrity and the ability of VLDL to interact with cell receptors are a function of not only VLDL constituents but also of the extent to which VLDL apoprotein E has been degraded.