RESUMO
Lipid A isolated from the Rickettsia typhi lipopolysaccharide (LPS) was investigated for its composition and structure using chemical analyses, gas chromatography-mass spectrometry (GC-MS), and electrospray ionization (ESI) combined with the tandem mass spectrometry (MS/MS). Our studies revealed a noticeable compositional and structural heterogeneity of lipid A with respect to the content of phosphate groups and the degree of acylation. It appeared that at least two molecular species were present in lipid A. The major species represented the hexaacyl lipid A consisting of the ß-(1--> 6)-linked D-glucosamine (GlcN) disaccharide backbone carrying two phosphate groups. One of them was linked to the glycosidic hydroxyl group of the reducing GlcN I and the other was ester linked to the O-4´ position of the non-reducing GlcN II. The primary fatty acids consisted of two 3-hydroxytetradecanoic [C14:0(3-OH)] and two 3-hydroxyhexadecanoic [C16:0(3-OH)] acids. The former were ester- and the latter amide-linked to both GlcN. Two secondary fatty acids were represented by the octadecanoic (C18:0) and hexadecanoic (C16:0) acids that were ester-linked at the N-2´ and O-3´ positions, respectively. In the minor lipid A species, ester-linked C18:0 was substituted by C16:0 at the C16:0(3-OH) of GlcN II. The R. typhi lipid A resembles structurally the classical forms of enterobacterial lipids A with high endotoxicity.
Assuntos
Lipídeo A/química , Rickettsia typhi/química , Acilação , Ácidos Graxos/análise , Cromatografia Gasosa-Espectrometria de Massas/métodos , Lipídeo A/análise , Lipídeo A/isolamento & purificação , Lipopolissacarídeos/análise , Lipopolissacarídeos/química , Lipopolissacarídeos/isolamento & purificação , Ácidos Mirísticos/química , Ácido Palmítico/química , Fosfatos/análise , Ácidos Esteáricos/química , Espectrometria de Massas em Tandem/métodosRESUMO
The composition and structure of lipid A isolated from the lipopolysaccharide (LPS) of Piscirickettsia salmonis were investigated by chemical analyses, gas chromatography/mass spectrometry (GCMS), and electrospray ionization (ESI) combined with the tandem mass spectrometry (MS/MS). Our study revealed moderate compositional and structural heterogeneity of lipid A with respect to the content of phosphate groups and 4-amino-4-deoxy-L-arabinopyranose (Ara4N) residues and with regard to the degree of acylation. It appeared that at least two molecular species were present in lipid A. The major species represented the hexaacyl lipid A consisting of the ss-(1--> 6)-linked D-glucosamine (GlcN) disaccharide backbone carrying two phosphate groups. The first one at the glycosidic hydroxyl group of the reducing GlcN I and the second one at the O-4' position of the non-reducing GlcN II. The primary fatty acids consisted of three 3-hydroxytetradecanoic [C14:0(3-OH)] and one 3-hydroxyhexadecanoic [C16:0(3-OH)] acids. The latter was amide-linked to GlcN I and one C14:0(3-OH) was amide-linked to GlcN II. Two secondary fatty acids were represented by C14:0(3-OH) and were equally distributed between the O-2' and O-3' positions. The phosphate group at O-4' carried a non-stoichiometric substituent Ara4N. The minor lipid A species contained exclusively C14:0(3-OH) with an asymmetric distribution (4+2) at GlcN II and GlcN I, respectively. The P. salmonis lipid A resembles structurally strongly endotoxic enterobacterial lipid A. This could be one of the reasons for the observed high endotoxicity of P. salmonis.
