Acyl carrier protein metabolism and regulation of fatty acid biosynthesis by Lactobacillus plantarum

Transcriptional Reprogramming at Genome-Scale of Lactobacillus plantarum WCFS1 in Response to Olive Oil Challenge

Dietary fats may exert selective pressures on Lactobacillus species, however, knowledge on the mechanisms of adaptation to fat stress in these organisms is still fragmentary. This study was undertaken to gain insight into the mechanisms of adaptation of Lactobacillus plantarum WCFS1 to olive oil challenge by whole genome transcriptional profiling using DNA microarrays. A set of 230 genes were differentially expressed by L. plantarum WCFS1 to respond to this vegetable oil. This response involved elements typical of the stringent response, as indicated by the induction of genes involved in stress-related pathways and downregulation of genes related to processes associated with rapid growth. A set of genes involved in the transport and metabolism of compatible solutes were downregulated, indicating that this organism does not require osmoprotective mechanisms in presence of olive oil. The fatty acid biosynthetic pathway was thoroughly downregulated at the transcriptional level, which coincided with a diminished expression of genes controlled by this pathway in other organisms and that are required for the respiratory function, pyruvate dehydrogenase activity, RNA processing and cell size setting. Finally, a set of genes involved in host-cell signaling by L. plantarum were differentially regulated indicating that olive oil can influence the expression of metabolic traits involved in the crosstalk between this bacterium and the host.

Role of the D-alanyl carrier protein in the biosynthesis of D-alanyl-lipoteichoic acid

D-Alanyl-lipoteichoic acid (D-alanyl-LTA) is a widespread macroamphiphile which plays a vital role in the growth and development of gram-positive organisms. The biosynthesis of this polymer requires the enzymic activation of D-alanine for its transfer to the membrane-associated LTA (mLTA). A small, heat-stable, and acidic protein that is required for this transfer was purified to greater than 98% homogeneity from Lactobacillus casei ATCC 7469. This protein, previously named the D-alanine-membrane acceptor ligase (V. M. Reusch, Jr., and F. C. Neuhaus, J. Biol. Chem. 246:6136-6143, 1971), functions as the D-alanyl carrier protein (Dcp). The amino acid composition, beta-alanine content, and N-terminal sequence of this protein are similar to those of the acyl carrier proteins (ACPs) of fatty acid biosynthesis. The isolation of Dcp and its derivative, D-alanyl approximately Dcp, has allowed the characterization of two novel reactions in the pathway for D-alanyl-mLTA biosynthesis: (i) the ligation of Dcp with D-alanine and (ii) the transfer of D-alanine from D-alanyl approximately Dcp to a membrane acceptor. It has not been established whether the membrane acceptor is mLTA or another intermediate in the pathway for D-alanyl-mLTA biosynthesis. Since the D-alanine-activating enzyme (EC 6.1.1.13) catalyzes the ligation reaction, this enzyme functions as the D-alanine-Dcp ligase (Dcl). Dcl also ligated the ACPs from Escherichia coli, Vibrio harveyi, and Saccharopolyspora erythraea with D-alanine. In contrast to the relaxed specificity of Dcl in the ligation reaction, the transfer of D-alanine to the membrane acceptor was highly specific for Dcp and did not occur with other ACPs. This transfer was observed by using only D-[14C]alanyl approximately Dcp and purified L. casei membranes. Thus, D-alanyl approximately Dcp is an essential intermediate in the transfer of D-alanine from Dcl to the membrane acceptor. The formation of D-alanine esters of mLTA provides a mechanism for modulating the net anionic charge in the cell wall.

Purification and characterization of acyl carrier protein from two cyanobacteria species

The acyl carrier protein (ACP), an essential protein cofactor for fatty acid synthesis, has been isolated from two cyanobacteria: the filamentous, heterocystous, Anabaena variabilis (ATCC 29211) and the unicellular Synechocystis 6803 (ATCC 27184). Both ACPs have been purified to homogeneity utilizing a three-column procedure. Synechocystis 6803 ACP was purified 1800-fold with 67% yield, while A. variabilis ACP was purified 1040-fold with 50% yield. Yields of 13.0 micrograms ACP/g Synechocystis 6803 and 9.0 micrograms ACP/g A. variabilis were achieved. Amino acid analysis indicated that these ACPs were highly charged acidic proteins similar to other known ACPs. Sequence analysis revealed that both cyanobacterial ACPs were highly conserved with both spinach and Escherichia coli ACP at the phosphopantetheine prosthetic group region. Examining the probability of alpha-helix and beta-turn regions in various ACPs, showed that cyanobacterial ACPs were more closely related to E. coli ACP than spinach ACP I. Immunoblot analysis and a competitive binding assay for ACP illustrated that both ACPs bound poorly to spinach ACP I antibody. SDS/PAGE and native PAGE of Synechocystis 6803 ACP and A. variabilis ACP showed that cyanobacteria ACPs co-migrated with E. coli ACP and had relative molecular masses of 18,100 and 17,900 respectively. Both native and urea gel analysis of acyl-ACP products from fatty acid synthase reactions demonstrated that bacterial ACPs and plant ACP gave essentially the same metabolic products when assayed using either bacterial or plant fatty acid synthase. A. variabilis and Synechocystis 6803 ACP could be acylated using E. coli acyl ACP synthetase.