Apolipoproteins and the structural organization of plasma lipoproteins: human plasma high density lipoprotein-3.

The structural properties and functions of the plasma high density lipoproteins (HDL) have recently become the center of attention, largely because of their possible participation in the control of both lipid metabolism and the pathogenesis of atherosclerosis. In the past, several structural models of HDL have been proposed, each trying to encompass the rather scanty information available on the physical and chemical properties of these lipoproteins and of their constituents. With the accumulation of relevant experimental data, the theoretical models became more detailed and hence more useful for guiding the experimental work. We recently described a general model of lipoprotein structure, based largely on compositional data of the serum lipoproteins and on the molecular volumes and surface areas of their lipid and polypeptide constituents; at that time, we made no attempt to describe the surface organization of the apoproteins. In recent years, empirical methods have been developed for prediction of the probability of secondary structure from amino acid sequence data. The reasonable success of some of these methods prompted us to apply them to the prediction of the secondary structure of the apolipoproteins at the lipoprotein surface. Thus, in the present studies we addressed ourselves to the question of themore » relationship between the secondary structure of apoproteins and the structure of plasma lipoproteins. We focused primarily on human HDL/sub 3/, because the primary amino acid sequence has been determined for its two main apolipoproteins: apoA-I and apoA-II. The C-peptides, although recognized as constituents of HDL/sub 3/, occur only in substoichiometric amounts. Since they probably have no essential structural role in HDL/sub 3/, they will only be considered in the context of the discussion.« less