32-33-34-35-bacteriohopanetetrol and diploptene

Sterols play an essential role in modulating bilayer structure and dynamics. Coarse-grained molecular dynamics parameters for cholesterol and related molecules are available for the Martini force field and have been successfully used in multiple lipid bilayer studies. In this work, we focus on the use of virtual sites as a means of increasing the stability of cholesterol and cholesterol-like structures. We improve and extend the Martini parameterization of sterols in four different ways: 1-the cholesterol parameters were adapted to make use of virtual interaction sites, which markedly improves numerical stability; 2-cholesterol parameters were also modified to address reported shortcomings in reproducing correct lipid phase behavior in mixed membranes; 3-parameters for ergosterol were created and adapted from cholesterols; and 4-parameters for the hopanoid class of bacterial polycyclic molecules were created, namely, for hopane, diploptene, bacteriohopanetetrol, and for their polycyclic base structure.

Topics: Molecular Conformation; Molecular Dynamics Simulation; Polycyclic Compounds; Sterols; Triterpenes

Sterols are the hallmarks of eukaryotic membranes where they are often found in specialized functional microdomains of the plasma membrane called lipid rafts. Despite some notable exceptions, prokaryotes lack sterols. However, growing evidence has suggested the existence of raft-like domains in the plasma membrane of bacteria. A structurally related family of triterpenoids found in some bacteria called hopanoids has long been assumed to be bacterial surrogates for sterols in membranes. Although the effect of sterols, in particular cholesterol, on lipid bilayers has been extensively characterized through experimental and simulation studies, those of hopanoids have hardly been investigated. In this study, molecular dynamics simulations are used to examine the effect of two hopanoids, diploptene (hop-22(29)-ene) and bacteriohopanetetrol ((32R,33S,34S)-bacteriohopane-32,33,34,35-tetrol), on a model bilayer. The results are compared with those obtained for cholesterol and a pure phosphatidylcholine bilayer. It is shown that diploptene and bacteriohopanetetrol behave very differently under the conditions simulated. Whereas bacteriohopanetetrol adopted a cholesterol-like upright orientation in the bilayer, diploptene partitioned between the two leaflets inside the bilayer. Analysis of various structural properties (area per lipid, electron density profile, tilt angle of the lipids, and conformation and order parameters of the phosphatidylcholine tails) in bacteriohopanetetrol- and cholesterol-containing bilayers indicates that the condensing and ordering effect of bacteriohopanetetrol is weaker than that of cholesterol. The simulations suggest that the chemical diversity of hopanoids may lead to a broader range of functional roles in bacterial membranes than sterols in eukaryotic membranes.

Topics: Cholesterol; Lipid Bilayers; Models, Molecular; Molecular Structure; Phosphorylcholine; Sterols; Triterpenes

A rapid and sensitive method for determination of various hopanoids in microorganisms is described. Tetrahydroxybacteriohopane (THBH), THBH-ether and -glycoside were acetylated with acetanhydride/pyridine and were separated on a C18 reversed-phase HPLC column with a gradient of acetonitrile in methanol and subsequent monitoring of the eluant at 206 nm. Quantification is based on peak area calculation by using purified bacteriohopanoids as external standards. A linear response is found from 10 to 20 micrograms bacteriohopanetetrol and for up to 200 micrograms ether and glycoside of THBH. Diplopterol and diploptene were determined by GLC after silylation with BSTFA/TMSCl in pyridine; the detector response is linear from 0.1 to 2 micrograms.

Topics: Bacteria; Chromatography, Gas; Chromatography, High Pressure Liquid; Glycosides; Reference Standards; Spectrophotometry, Ultraviolet; Triterpenes