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Asymmetric Spontaneous Intercalation of Lutein into a Phospholipid Bilayer, a Computational Study.

ABSTRACT: Lutein, a hydroxylated carotenoid, is a pigment synthesised by plants and bacteria. Animals are unable to synthesise lutein, nevertheless, it is present in animal tissues, where its only source is dietary intake. Both in plants and animals, carotenoids are associated mainly with membranes where they carry out important physiological functions. Their trafficking to and insertion into membranes are not well recognised due to experimental difficulties. In this paper, a computational approach is used to elucidate details of the dynamics and energetics of lutein intercalation from the water to the phospholipid bilayer phase. The dynamics is studied using molecular dynamics simulation, and the energetics using umbrella sampling. Lutein spontaneous insertion into the bilayer and translocation across it proceed via formation of hydrogen bonds between its hydroxyl groups and water and/or phospholipid oxygen atoms as well as desolvation of its polyene chain. As lutein molecule is asymmetric, its bilayer intercalation is also asymmetric. The course of events and timescale of the intercalation are different from those of helical peptides. The time of full lutein intercalation ranges from 20 to 100 ns and its final orientation is predominately vertical. Nevertheless, some lutein molecules are in the final horizontal position and some aggregate in the water phase and remain there for the whole simulation time. The highest energy barrier for the intercalation process is ~2.2 kcal/mol and the energy gain is ~18 kcal/mol. The results obtained for lutein can be applied to other xanthophylls and molecules of a similar structure.

SUBMITTER: Makuch K

PROVIDER: S-EPMC6465758 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:This study aims to investigate the interactions appearing when the beta-2-glycoprotein-1 binds to a lipid bilayer. The inter- and intra-molecular forces acting between the two macromolecular systems have been investigated using a molecular dynamics simulation method. The importance of water bridges has also been addressed. Additionally, the viscoelastic response of the bilayer has been studied. In detail, the (saturated-chain) 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and (unsaturated-chain) 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) bilayers have been chosen to test their behavior near the protein. Both of the lipids have a polar head but different chemical structures and are similar to the main phospholipids present in the synovial fluid. This study is meaningful for further explaining the worsening friction properties in articular cartilage, as the inactivation of phospholipid bilayers by beta-2-glycoprotein-1 is believed to be a cause of the destruction of cartilage in most rheumatic diseases and osteoarthritis. It was found that the protein binds stronger to the DPPC bilayer than to the POPE, but in both cases, it has the potential to change the local bilayer stability. Nevertheless, the binding forces are placed within a small area (only a few lipids contribute to the binding, creating many interactions). However, together, they are not stronger than the covalent bonds between C-O, thus, potentially, it is possible to push the lipids into the bilayer but detaching the lipids' heads from the tail is not possible. Additionally, the protein causes water displacement from the vicinity of the bilayer, and this may be a contributor to the instability of the bilayer (disrupting the water bridges needed for the stabilization of the bilayer, especially in the case of DPPC where the heads are not so well stabilized by H-bonds as they are in POPE). Moreover, it was found that the diffusivity of lipids in the DPPC bilayer bound to the protein is significantly different from the diffusivity of the ones which are not in contact with the protein. The POPE bilayer is stiffer due to intramolecular interactions, which are stronger than in the DPPC; thus, the viscous to elastic effects in the POPE case are more significant than in the case of the DPPC. It is, therefore, harder to destabilize the POPE bilayer than the DPPC one.

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Asymmetric Spontaneous Intercalation of Lutein into a Phospholipid Bilayer, a Computational Study.

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