Human apolipoprotein E3 in aqueous solution. I. Evidence for two structural domains.

摘要: The stability and structure of human apolipoprotein (apo) E3 in aqueous solution were investigated by guanidine HCl denaturation limited proteolysis. curve, as monitored circular dichroism spectroscopy, was biphasic; the two transition midpoints occurred at 0.7 2.5 M HCl, indicating that there are stable intermediate structures unfolding apoE. Limited proteolysis apoE with five enzymes demonstrated proteolytically resistant regions, an amino-terminal domain (residues 20-165) a carboxyl-terminal 225-299). region between them highly susceptible to proteolytic cleavage. Because their similarity 1-191) 216-299) thrombolytic fragments used models for domains. Guanidine carboxyl- gave 2.4 respectively. results establish domains identified correspond detected protein experiments. Therefore, useful free energies calculated from curves intact or model approximately 4 8-12 kcal/mol domains, value is similar those previously characterized apolipoproteins, whereas considerably higher resembles soluble globular proteins. These studies suggest that, solution, unlike other apolipoproteins it contains independently folded structural markedly different stabilities: domain, separated residues may act hinge region.