Subsystem: D-Alanyl Lipoteichoic Acid Biosynthesis

This subsystem's description is:

Gram-positive organisms contain a cell wall that is rife with various constituents, one of the most important of these being D-alanyl-lipoteichoic acid; although not present in all gram-positive bacteria those that lack this polymer have similar replacements. LTA can be broken into three groups: Group I LTA’s (Enterococcus faecalis and Lactobacillus rhamnosus) consist of poly (Gro-P) attached to a glycolipid, Group II LTA’s have a –GalGal-Gro-P repeating unit (Lactococcus garvieae), and Group III’s LTA’s have a Gal-Gro-P repeating unit (Clostridium innocuum). Gro-P tends to have alanyl esters attached to it, which are unyielding D in configuration.

Four proteins are required for the synthesis of D-alanyl-lipoteichoic acid, all of which come form the dlt operon. The four major genes under this operon are: DltA, DltB, DltC, and DltD. Two of these are the 56-kDa D-alanine:D-alanyl carrier protein ligase (AMP forming) (Dcl) and the 8.8-kDa D-alanyl carrier protein (Dcp). First Dcp (DltC) joins with LTA and helps in carrying LTA across a putative channel provided by DltB. After LTA has tranversed the membrane DltD allowed for docking by Dcp and Dcl (DltA) and D-alanylation results.Thus, incorporation of D-alanine is accomplished in the two-step reaction sequence:

a) ATP + D-alanine + Dcp ---> AMP + PPi + D-alanyl-Dcp

b) b) D-alanyl-Dcp + membrane-associated LTA <==> membrane- associated D-alanyl-LTA + Dcp

*****Variant Codes******

1- Full set as in B. subtilis
2- missing Dcp as in Staphylococcus aureus subsp. aureus NCTC 8325

For more information, please check out the description and the additional notes tabs, below

DiagramFunctional RolesSubsystem SpreadsheetDescriptionAdditional Notes 

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Gram-positive organisms contain a cell wall that is rife with various constituents, one of the most important of these being D-alanyl-lipoteichoic acid; although not present in all gram-positive bacteria those that lack this polymer have similar replacements. LTA can be broken into three groups: Group I LTA’s (Enterococcus faecalis and Lactobacillus rhamnosus) consist of poly (Gro-P) attached to a glycolipid, Group II LTA’s have a –GalGal-Gro-P repeating unit (Lactococcus garvieae), and Group III’s LTA’s have a Gal-Gro-P repeating unit (Clostridium innocuum). Gro-P tends to have alanyl esters attached to it, which are unyielding D in configuration.

Four proteins are required for the synthesis of D-alanyl-lipoteichoic acid, all of which come form the dlt operon. The four major genes under this operon are: DltA, DltB, DltC, and DltD. Two of these are the 56-kDa D-alanine:D-alanyl carrier protein ligase (AMP forming) (Dcl) and the 8.8-kDa D-alanyl carrier protein (Dcp). First Dcp (DltC) joins with LTA and helps in carrying LTA across a putative channel provided by DltB. After LTA has tranversed the membrane DltD allowed for docking by Dcp and Dcl (DltA) and D-alanylation results.Thus, incorporation of D-alanine is accomplished in the two-step reaction sequence:

a) ATP + D-alanine + Dcp ---> AMP + PPi + D-alanyl-Dcp

b) b) D-alanyl-Dcp + membrane-associated LTA <==> membrane- associated D-alanyl-LTA + Dcp

*****Variant Codes******

1- Full set as in B. subtilis
2- missing Dcp as in Staphylococcus aureus subsp. aureus NCTC 8325
This Subsystem was encoded by Elliot Miller ( University of Florida)
Notes copied from Subsystem: D-alanyl_lipoteichoic_acid

*****OVERVIEW:**********

In terms of the organization of the dlt operon itself, it is shown that both dltA/dltB and dltC/dltD overlap by approximately 1 to 4 bases pairs. In addition, it has been shown that several unique traits exist for this operon depending upon the species observed. Streptococcus agalactiae, for instance, has two regulatory genes dltR, which belongs to the OmpR family of regulatory proteins, and dltS, which is a putative histidine kinase the may sense environmental signals (2). Furthermore, it has been shown that Bacillus subtilis contains a dltE gene that encodes an oxidoreductase; this gene does not appear to be involved in D-alanylation of the lipoteichoic acid (3).
The purposes of D-alanyl lipteichoic acid are multifold. First, LTA aids in the regulation of the hydrolysis actions of autolysins. In addition, it is responsible for keeping cation homeostatis and in the uptake of metal cations needed for cellular function. Finally, LTA’s are needed to in order to “define the electromechanical properties of the cell well.”

******OBSERVATIONS:*******

From the data obtained through SEED it quickly became evident that the functional roles required for the production of D-alanyl lipoteichoic acid occur in a wide varity of organisms. Whats more is that not only are all functional roles observed in most instances but the functional roles are highly clustered. This is a good indication that the functional roles are legitimate with regard to the model organism (Bacillus subtilis) versus the other organisms found to contain this subsystem. One aspect of this comparison indicates that a few organisms lack Dcp which is the carrier protein responsible for aiding the transport of the lipteichoic acid across the channel. This is most likely the least crucial of the functional groups and so it is understandable that if any role was absent, that it would be this one.

It appears that the members of Bacillaceae, although closely related to Bacillus, lack the functional roles that are needed for D-alanylation of the lipoteichoic acid. Perhaps another similar mechanism is implemented, although this is merely conjecture and is neither supported nor refuted by existing evidence extrapolated through SEED. More unusual, Bacillus halodurans also appears to be missing these functional roles, which was highly unexpected considering the prevelance of the roles across many different Baccilli. Most Clostridium strains appear to lack this system; the exception to this rule is Clostridium difficile, which contains all four functional roles in a completely clustered fashion.


========References ===========================

1a. Kovács M, Halfmann A, Fedtke I, Heintz M, Peschel A, Vollmer W, Hakenbeck R, Brückner R. A functional dlt operon, encoding proteins required for incorporation of d-alanine in teichoic acids in gram-positive bacteria, confers resistance to cationic antimicrobial peptides in Streptococcus pneumoniae. J Bacteriol. 2006 Aug;188(16):5797-805. PMID: 16885447

1. Francis C. Neuhaus and James Baddiley (2003). “A Continuum of Anionic Charge: Structures and Functions of D-Alanyl-Teichoic acids in Gram Positive Bacteria.” Microbiology and Molecular Biology Reviews. p. 686-723. PMID: 14665680

2. Poyart, C., M.-C. Lamy, C. Boumaila, F. Fiedler, and P. Trieu-Cuot. 2001. Regulation of D-alanyl lipoteichoic acid biosynthesis in Streptococcus agalactiae involves a novel two-component regulatory system. J. Bacteriol. 183:6324-6334.

3. Glaser, P., F. Kunst, M. Arnaud, M.-P Courdart, W. Gonzales, M.-F. Hullo, M. Ionescu, B. Lubochinsky, L. Marcelino, I. Mozer, E. Presecan, M. Santana, E. Schneider, J. Schweizer, A. Vertes, G. Rapoport, and A. Danchin. 1993. Bacillus subtilis genome project: cloning and sequencing the 97 kb region from 325 degrees to 333 degrees. Mol. Microbiol. 10:371-384.