Liprotides: Nano-Sized Cytotoxic Protein-Fatty Acid Complexes with a Core-Shell or Multi-Layer Structure

Abstract

The retroviral polyprotein Gag is an essential component for the formation of virus in infected cells. HIV-1 Gag is expressed in the cytoplasm, migrates to the cellular periphery and eventually targets the surface of the plasma membrane (PM), where assembly of immature virus occurs. The N-terminal matrix (MA) domain of Gag is the structural motif that mediates assembly on the PM. Distinct molecular mechanisms complement each other in positioning the protein in an orientation productive for assembly on the correct target membrane: electrostatic interaction between a patch of basic residues on the protein and anionic membrane lipids, hydrophobic interaction between MA's myristoylated N-terminus and the membrane, and specific binding of the protein to phophatidylinositol-4,5-bisphosphate (PI(4,5)P2) selectively enriched in the PM. A comparative study of non-myristoylated (-myr) and myristoylated (þmyr) MA association with well-defined membrane models of progressively higher compositional complexity was carried out. The systematic characterization of MA binding reveals that the various membrane components are highly cooperative in their interaction with the protein. More specifically, surface plasmon resonance shows weak binding of -myrMA to membranes containing physiological amounts of phosphatidylserine lipids. A significant increase in membrane affinity is observed for þmyrMA, which demonstrates that PI(4,5)P2 is not required for myristoyl exposure and membrane insertion. We find that þmyrMA has a preference to associate with cholesterol-rich membrane regions, increasing both binding affinity and total surface coverage of protein. PI(4,5)P2, which associates to a specific binding site on MA, was identified as the strongest single contributor to membrane binding. Our results show that the most complex lipid composition, which approaches the complexity of the biological membrane, is most effective in attracting the MA protein. This might explain the selective recruitment of those lipids into the viral membrane shell.

Preparation and characterization of liprotides prepared from protein extracts of mung beans (Vigna radiata (L.))

“…This type of core-shell structure was first reported by Håkansson et al (1995) via the synthesis of the cytotoxic human alpha-lactalbumin made lethal to tumor cells, which they called HAMLET, complex consisting of a cis-monounsaturated OA surrounded by alpha-lactalbumin (aLA). Over the years, various unrelated proteins and different kinds of fatty acids have been used to prepare these complexes having a core-shell structure or even larger multi-layered-structure, i.e., extra layer of fatty acids and proteins enveloping the inner core-shell body, when a higher fatty acid-protein molar ratio is used (Frislev et al, 2016). Liprotides are known for their cancer cell cytotoxicity, which have been proposed to arise from the transfer of the fatty acid, e.g.…”