Structural analysis by reductive cleavage with LiAlH4 of an allyl ether choline‐phospholipid, archaetidylcholine, from the hyperthermophilic methanoarchaeon Methanopyrus kandleri

Abstract

A choline-containing phospholipid (PL-4) in Methanopyrus kandleri cells was identified as archaetidylcholine, which has been described by Sprott et al. (1997). The PL-4 consisted of a variety of molecular species differing in hydrocarbon composition. Most of the PL-4 was acid-labile because of its allyl ether bond. The identity of PL-4 was confirmed by thin-layer chromatography followed by positive staining with Dragendorff reagent and fast-atom bombardment-mass spectrometry. A new method of LiAlH4 hydrogenolysis was developed to cleave allyl ether bonds and recover the corresponding hydrocarbons. We confirmed the validity of the LiAlH4 method in a study of the model compound synthetic unsaturated archaetidic acid (2,3-di-O-geranylgeranyl-sn-glycerol-1-phosphate). Saturated ether bonds were not cleaved by the LiAlH4 method. The hydrocarbons formed following LiAlH4 hydrogenolysis of PL-4 were identified by gas-liquid chromatography and mass spectrometry. Four kinds of hydrocarbons with one to four double bonds were detected: 47% of the hydrocarbons had four double bonds; 11% had three double bonds; 14% had two double bonds; 7% had one double bond; and 6% were saturated species. The molecular species composition of PL-4 was also estimated based on acid lability: 77% of the molecular species had two acid-labile hydrocarbons; 11% had one acid-labile and one acid-stable hydrocarbon; and 11% had two acid-stable hydrocarbons. To our knowledge, this is the first report of a specific chemical degradation method for the structural analysis of allyl ether phospholipid in archaea.

In Vitro Study of Lipid Biosynthesis in an Anaerobically Methane-Oxidizing Microbial Mat

“…Monounsaturated archaeols were shown to originate from hydroxyarchaeol under acidic conditions as laboratory conversion products (9). However, recent studies described this compound as a constitutive membrane lipid of the hyperthermophilic methanogen Methanopyrus kandleri (28). Under the conditions used in this study (mild alkaline hydrolysis), conversion of hydroxyarchaeol to unsaturated archaeol has not been reported and was successfully applied to analysis of hydroxyarchaeol-containing samples (25,36).…”

Recent Advances in Structural Research on Ether Lipids from Archaea Including Comparative and Physiological Aspects

“…The results were almost consistent with the hydrocarbon composition described as above. 34) This was the first example of estimation of molecular species composition of archaeal ether phospholipid. In addition to archaetidylcholine, six phospholipids, including phosphorylated N-acetylglucosaminyl archaeol, archaetidylinositol, hydroxyarchaetidylserine, hydroxyarchaetidylethanolamine or unsaturated archaetidylglycerol, A, C40 isoprenoid with three cyclopentane rings at an unusual position; 23) B, C31 non-isoprenoid hydrocarbon with three methyl branches; 25) C, C30 non-isoprenoid hydrocarbon with a cyclopentane ring; 25) D, C35 hybrid hydrocarbon apparently formed by combination of C20 isoprenoid and iso-branched C15 non-isoprenoid hydrocarbon; 25) E, cyclic archaeol with two cylopentane rings.…”

“…But Sprott et al 33) have shown the presence of unsaturated archaeol-based phospholipids, the most abundant of which is unsaturated archaetidylcholine, in the same archaeon by MS of total lipids. Nishihara et al 34) reexamined HCl-methanolysis for choline-containing phospholipids, and they found that most of the phospholipids were degraded during methanolysis but that a small amount of the lipid remained intact, composed of saturated archaeol as a core. They assumed that the aciddegraded portion of the phospholipids was composed of acid-labile allyl ether core lipids.…”

“…To confirm this assumption, they developed a LiAlH 4 reductive cleavage method of allyl ether bonds. 34) Allyl ether-bonded hydrocarbon was released as intact hydrocarbon by their method. The products were identified as unsaturated isoprenoid hydrocarbons with one, two, three, or four double bonds by GLC-MS.…”

“…Unsaturated archaeol (geranylgeranyl group-containing archaeol) is present in psychrophilic Methanococcoides burtonii 37) that can grow at 2 C as well as in hyperthermophilic Methanopyrus kandleri (98 C). 34) The same ether lipids of archaea can be utilized at both high and low temperatures because of their liquid crystalline phase and low permeability in a wide range of temperatures. Such a lipid can be called a ''heat tolerant'' lipid.…”