Menaquinones (naphthoquinones, Vitamin K, abbreviated as MK) are isoprenoids that play key roles in the respiratory electron transport system of some prokaryotes by shuttling electrons between membrane-bound protein complexes and act as electron acceptors and donors. A truncated MK/Vitamin K analog, menaquinone-2 (MK-2), was synthesized and the studies presented herein characterize the conformation of the hydrophobic MK-2 molecule in various environments. Using 2D NMR spectroscopy, we established for the first time that MK-2 has a folded conformation defined by the isoprenyl side-chain folding back over the naphthoquinone in a U-shape, which depends on the specific environmental conditions found in different organic solvents. We used molecular mechanics to illustrate conformations determined from the 2D NMR experiments. Furthermore, MK-2 was found to associate with the interface of model membranes represented by Langmuir phospholipid monolayers and Aerosol-OT (AOT) reverse micelles. MK-2 adopts a slightly different U-shaped conformation within reverse micelles compared to within organic solution, which is in sharp contrast to the extended conformations illustrated in literature for MKs.

Vitamin K analog, menaquinone-2, adopts a folded conformation in solution and at a model membrane interface

2019 Spring National Meeting

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