D-Alanyl-lipoteichoic acid (D-alanyl-LTA) contains D-alanine ester residues which control the ability of this polymer to chelate Mg2". In Lactobacillus casei a two-step in vitro reaction sequence catalyzed by the D-alanine-activating enzyme and D-alanine:membrane acceptor ligase incorporates D-alanine into membrane acceptor. In this paper we provide additional evidence that the in vitro system

Lipophilic and hydrophilic D-alanyl-lipoteichoic acids are elongated in Lactobacillus casei by the transfer of sn-glycerol 1-phosphate units from phosphatidylglycerol to the poly(glycerophosphate) moiety of the polymer. These sn-glycerol 1phosphate units are added to the end of the poly(glycerophosphate) which is distal to the glycolipid anchor; 1,2-diglyceride results from this addition. The presence of a diglyceride kinase was suggested by the ATP-dependent phosphorylation of 1,2-diglyceride to phosphatidic acid. Inorganic phosphate was used to initiate the synthesis of lipophilic lipoteichoic acid (LTA) and the elongation of both lipophilic and hydrophilic LTA. Three observations suggest that phosphate and other anions play a role in the in vitro synthesis of LTA and its precursors. First, the conversion of 1,2-diglyceride to phosphatidic acid by diglyceride kinase was stimulated. Second, the synthesis of phosphatidylglycerol was increased. Third, the elongation of lipophilic and hydrophilic LTA was enhanced. These observations indicated that one effect of phosphate might be to enhance the utilization of 1,2-diglyceride for the synthesis of phosphatidic acid. This phospholipid is a precursor of phosphatidylglycerol, the donor of sn-glycerol 1-phosphate for elongation of LTA. Phosphatidylglycerol (PG) has been proposed to be the donor of sn-glycerol 1-phosphate (GroP) units of the poly(glycerophosphate) moiety of lipoteichoic acid (LTA) (8,9,13,14) according to the following reaction: tion would result in a cycling of the diglyceride moiety of this phospholipid.The goals of these experiments with Lactobacillus casei were to characterize further the effect of phosphate on the assembly of the LTA, PG + LTA-poly(glycerophosphate)" -* LTA-poly(glycerophosphate),+1 + 1,2-diglyceride Inorganic phosphate stimulates both the synthesis of PG and the elongation of D-alanyl-lipophilic LTA in vitro (4). These observations supported the proposed role for PG in the elongation of LTA.During the elongation of LTA, one of the reaction products is 1,2-diglyceride. Significant amounts of this diglyceride might be expected to accumulate during chain elongation. Since large amounts of diglyceride are not commonly found in bacteria (25), it is proposed that the diglyceride is either degraded or reutilized for phospholipid synthesis. A diglyceride kinase similar to that found in Escherichia coli (24) could phosphorylate the diglyceride to phosphatidic acid, a known precursor of PG (25). This phosphorylat Present address: College of Dentistry, University of Illinois at the Medical Center, Chicago, IL 60612. to determine the site of the addition of GroP units to the growing polymer, and to suggest a fate for the 1,2-diglyceride. Toluene-treated cells were used to demonstrate the synthesis and elongation of D-alanyl-LTA as well as the synthesis of various phospholipids. These cells, which are permeable to GroP, ATP, and Dalanine, synthesized LTA and phospholipids in significant amounts. For detecting diglyceride kinase, membranes were u...

D-Alanyl-lipoteichoic acid (D-alanyl-LTA) from Lactobacillus casei contains a poly(glycerol phosphate) moiety that is selectively acylated with D-alanine ester residues. To characterize further the mechanism of D-alanine substitution, intermediates were sought that participate in the assembly of this LTA. From the incorporation system utilizing either toluene-treated cells or a combination of membrane fragments and supernatant fraction, a series of membrane-associated D-[14C]alanyl-lipophilic compounds was found. The assay of these compounds depended on their extractability into monophasic chloroform-methanol-water (0.8:3.2:1.0, vol/vol/vol) and subsequent partitioning into chloroform. Four lines of evidence suggested that the D-alanyl-lipophilic compounds are intermediates in the synthesis of D-alanyl-LTA. First, partial degradation of the poly(glycerol phosphate) moiety of D-alanyl-LTA by phosphodiesterase II/phosphatase from Aspergillus niger generated a series of D-alanyl-lipophilic compounds similar to those extracted from the toluene-treated cells during the incorporation of D-alanine. Second, enzymatic degradation of the D-alanyl-lipophilic compounds by the above procedure gave D-alanyl-glycerol, the same degradation product obtained from D-alanyl-LTA. Third, the incorporation of D-alanine into these compounds required the same components as the incorporation of D-alanine into membrane-associated D-alanyl-LTA. Fourth, the phosphate-induced loss of D-[14C]alanine-labeled lipophilic compounds could be correlated with the stimulation of phosphatidylglycerol synthesis in the presence of excess phosphate. We interpreted these experiments to indicate that the D-alanyl-lipophilic compounds are D-alanyl-LTA with short polymer chains and are most likely intermediates in the assembly of the completed polymer, D-alanyl-LTA.

Lipoteichoic acid (LTA) from Lactobacilus casei contains poly(glycerophosphate) substituted with D-alanyl ester residues. The distribution of these residues in the in vitro-synthesized polymer is uniform. Esterification of LTA with D-alanine may occur in one of two modes: (i) addition at random or (ii) addition at a defined locus in the poly(glycerophosphate) chain followed by redistribution of the ester residues. A time-dependent transacylation of these residues from D_[14C]alanyl-lipophilic LTA to hydrophilic acceptor was observed. The hydrophilic acceptor was characterized as D-alanyl-hydrophilic LTA. This transacylation requires neither ATP nor the D-alanine incorporation system, i.e., the D-alanine activating enzyme and D-alanine:membrane acceptor ligase. No evidence for an enzyme-catalyzed transacylation reaction was observed. We propose that this process of transacylation may be responsible for the redistribution of D-alanyl residues after esterification to the poly(glycerophosphate). As a result, it is difficult to distinguish between these proposed modes of addition.on July 16, 2020 by guest

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