lipid-a and 3-hydroxydodecanoic-acid

PagL and LpxO are enzymes that modify lipid A. PagL is a 3-O deacylase that removes the primary acyl chain from the 3 position, and LpxO is an oxygenase that 2-hydroxylates specific acyl chains in the lipid A. pagL and lpxO homologues have been identified in the genome of Bordetella bronchiseptica, but in the current structure for B. bronchiseptica lipid A the 3 position is acylated and 2-OH acylation is not reported. We have investigated the role of B. bronchiseptica pagL and lpxO in lipid A biosynthesis. We report a different structure for wild-type (WT) B. bronchiseptica lipid A, including the presence of 2-OH-myristate, the presence of which is dependent on lpxO. We also demonstrate that the 3 position is not acylated in the major WT lipid A structures but that mutation of pagL results in the presence of 3-OH-decanoic acid at this position, suggesting that lipid A containing this acylation is synthesized but that PagL removes most of it from the mature lipid A. These data refine the structure of B. bronchiseptica lipid A and demonstrate that pagL and lpxO are involved in its biosynthesis.

Topics: Bacterial Proteins; Bordetella bronchiseptica; Carboxylic Ester Hydrolases; Lauric Acids; Lipid A; Myristates; Oxygenases

The first step of lipid A biosynthesis is catalyzed by LpxA in Escherichia coli (EcLpxA), an acyltransferase selective for UDP-GlcNAc and R-3-hydroxymyristoyl-acyl carrier protein (ACP). Leptospira interrogans LpxA (LiLpxA) is extremely selective for R-3-hydroxylauroyl-ACP and an analogue of UDP-GlcNAc, designated UDP-GlcNAc3N, in which NH(2) replaces the GlcNAc 3-OH group. EcLpxA does not discriminate between UDP-GlcNAc and UDP-GlcNAc3N; however, E. coli does not make UDP-GlcNAc3N. With LiLpxA, R-3-hydroxylauroyl-methylphosphopantetheine efficiently substitutes for R-3-hydroxylauroyl-ACP. We now present crystal structures of free LiLpxA and its complexes with its product UDP-3-N-(R-3-hydroxylauroyl)-GlcNAc3N and with its substrate R-3-hydroxylauroyl-methylphosphopantetheine. The positions of the acyl chains of the R-3-hydroxylauroyl-methylphosphopantetheine and the UDP-3-N-(R-3-hydroxylauroyl)-GlcNAc3N are almost identical and are similar to that of the acyl chain in the EcLpxA/UDP-3-O-(R-3-hydroxymyristoyl)-GlcNAc complex. The selectivity of LiLpxA for UDP-GlcNAc3N may be explained by the orientation of the backbone carbonyl group of Q68, which differs by approximately 82 degrees from the corresponding Q73 carbonyl group in EcLpxA. This arrangement provides an extra hydrogen-bond acceptor for the 3-NH(2) group of UDP-GlcNAc3N in LiLpxA. The R-3-hydroxylauroyl selectivity of LiLpxA is explained by the position of the K171 side chain, which limits the length of the acyl-chain-binding groove. Our results support the role of LiLpxA H120 (which corresponds to EcLpxA H125) as the catalytic base and provide the first structural information about the orientation of the phosphopantetheine moiety during LpxA catalysis.

Topics: Acyltransferases; Biocatalysis; Catalytic Domain; Crystallography, X-Ray; Fatty Acids; Hydrogen Bonding; Kinetics; Lauric Acids; Leptospira interrogans; Lipid A; Models, Molecular; Pantetheine; Protein Conformation; Protein Structure, Secondary; Recombinant Proteins; Substrate Specificity; Uridine Diphosphate N-Acetylglucosamine

The lipopolysaccharide (LPS) of the outer membrane of Caulobacter crescentus was purified and analyzed. Two distinct strains of the species, NA 1000 and CB2A, were examined; despite differences in other membrane-related polysaccharides, the two gave similar LPS composition profiles. The LPS was the equivalent of the rough LPS described for other bacteria in that it lacked the ladder of polysaccharide-containing species that results from addition of variable amounts of a repeated sequence of sugars, as detected by gel electrophoresis in smooth LPS strains. The purified LPS contained two definable regions: (i) an oligosaccharide region, consisting of an inner core of three residues of 2-keto-3-deoxyoctonate, two residues of alpha-L-glycero-D-mannoheptose, and one alpha-D-glycero-D-mannoheptose unit and an outer core region containing one residue each of alpha-D-mannose, alpha-D-galactose, and alpha-D-glucose, with the glucose likely phosphorylated and (ii) a region equivalent to the lipid A region of the archetype, consisting primarily of an esterified fatty acid, 3-OH-dodecanoate. The lipid A-like region was resistant to conclusive analysis; in particular, although a variety of analytical methods were used, no amino sugars were detected, as is found in the lipid A of the LPS of most bacteria.

Topics: Antigens, Bacterial; Caulobacter crescentus; Cell Membrane; Galactose; Genetic Variation; Glucose; Heptoses; Lauric Acids; Lipid A; Lipids; Lipopolysaccharides; Mannose; Oligosaccharides; Sugar Acids

The fatty acid composition of the bound lipids of 17 strains from Phenylobacterium immobile was investigated. Ester-linked 3-hydroxy-5c-dodecenoic acid was found to be the major substituent in the lipopolysaccharide. Therefore the occurrence of this unusual acid can be taken as a useful marker for the determination of P. immobile by simple fatty acid analysis. Lipid A backbone was found to consist of 2,3-diamino-2,3-dideoxy-D-glucose, which up to this time has only been detected in group I of purple nonsulfur bacteria and their non-phototrophic relatives. A convenient chemical synthesis for 3-hydroxy-5c-dodecenoic acid is described. The polysaccharide region of P. immobile strain K2 lipopolysaccharide was investigated. The methods used included gel filtration procedures, methylation analysis, periodate oxidation, Smith degradation, oxidation with chromium trioxide and enzymic degradations of the isolated oligosaccharide. We found that strain K2 has a rough-type lipopolysaccharide, devoid of an O-specific side chain. For the core oligosaccharide the following structure is proposed: (Formula: see text) beta-D-Glcp(1-3)-L-alpha-D-Hep rho(1-3)-L-alpha-D-Hep rho(1-3-L-alpha-D-Hep rho(1-4/5)dOclA.

Topics: Carbohydrate Conformation; Chemical Phenomena; Chemistry; Chromatography, Gel; Fatty Acids; Gram-Negative Bacteria; Lauric Acids; Lipid A; Lipids; Lipopolysaccharides; Molecular Weight; Oligosaccharides