Apolipoproteins structural motif

The amphipathic helix, in which residues are spaced so that the helical periodicity places hydrophobic side chains on one side of the helix and hydrophilic side chains on the other, is a common structural motif used by the peripheral apolipoproteins to bind lipid (Segrest et al., 1992) it is also a structural element present in globular proteins (Perutz et al., 1965). 

THE AMPHIPATHIC a HELIX A MULTIFUNCTIONAL STRUCTURAL MOTIF IN PLASMA APOLIPOPROTEINS... 

What, if anything, can be said about the evolutionary relationship between apoLp-III and exchangeable vertebrate apolipoproteins Both bind to lipoproteins and seem to have similar structural motifs. Whether apoLp-III is the ancestor of the vertebrate proteins can not be stated with... 

In humans, apoA-IV is found primarily in the free protein (nonlipoprotein) portion of plasma. Although the reason is not clear, it is possible that the lack of class A motif in the amphipathic helical domains of human apoA-IV causes it to associate poorly with the lipoprotein surface. In rats, however, apoA-IV is seen on HDLs. Examination of individual amphipathic helical domains of rat apoA-IV does show the presence of the class A motif in its structure, thus supporting our hypothesis that the class A motif is essential for binding of apolipoproteins to lipoproteins. 

The key structural features predicted for the amphipathic helix by the original model (Segrest et al., 1974) enabled three laboratories to study independently how amino acid variability determined the properties of the amphipathic helix (Kanellis et al., 1980 Fukushima et al., 1980 Sparrow et al., 1981). The strategy adapted by these investigators was based, not on the primary sequence of naturally occurring apolipoproteins, but on incorporating the periodicity of the secondary structural features of the amphipathic helix motif into the sequences of the peptide analogs. 

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