Teichoic acid

Teichoic acids (cf. Greek τεῖχος, teīkhos, 'wall', to be specific a fortification wall, as opposed to τοῖχος, toīkhos, a regular wall) are bacterial copolymers of glycerol phosphate or ribitol phosphate and carbohydrates linked via phosphodiester bonds. Teichoic acids (cf. Greek τεῖχος, teīkhos, 'wall', to be specific a fortification wall, as opposed to τοῖχος, toīkhos, a regular wall) are bacterial copolymers of glycerol phosphate or ribitol phosphate and carbohydrates linked via phosphodiester bonds. Teichoic acids are found within the cell wall of most Gram-positive bacteria such as species in the genera Staphylococcus, Streptococcus, Bacillus, Clostridium, Corynebacterium, and Listeria, and appear to extend to the surface of the peptidoglycan layer. They can be covalently linked to N-acetylmuramic acid or a terminal D-alanine in the tetrapeptide crosslinkage between N-acetylmuramic acid units of the peptidoglycan layer, or they can be anchored in the cytoplasmic membrane with a lipid anchor. Teichoic acids that are anchored to the lipid membrane are referred to as lipoteichoic acids (LTAs), whereas teichoic acids that are covalently bound to peptidoglycan are referred to as wall teichoic acids (WTA). The most common structure of Wall teichoic acids are a ManNAc(β1→4)GlcNAc disaccharide with one to three glycerol phosphates attached to the C4 hydroxyl of the ManNAc residue followed by a long chain of glycerol- or ribitol phosphate repeats. Variations come in the long chain tail, which generally include sugar subunits being attached to thee sides or the body of the repeats. Four types of WTA repeats have been named, as of 2013. Lipoteichoic acids follow a similar pattern of putting most variation in the repeats, although the set of enzymes used are different, at least in the case of Type I LTA. The repeats are anchored onto the membrane via a (di)glucosyl-diacylglycerol (Glc(2)DAG) anchor. Type IV LTA from Streptococcus pneumoniae represents a special case where both types intersect: after the tail is synthesized with a undecaprenyl phosphate (C55-P) intermediate 'head', different TagU/LCP (LytR-CpsA-Psr) family enzymes either attaches it to the wall to form a WTA or to the GlcDAG anchor. The main function of teichoic acids is to provide rigidity to the cell-wall by attracting cations such as magnesium and sodium. Teichoic acids can be substituted with D-alanine ester residues, or D-glucosamine, giving the molecule zwitterionic properties. These zwitterionic teichoic acids are suspected ligands for toll-like receptors 2 and 4. Teichoic acids also assist in regulation of cell growth by limiting the ability of autolysins to break the β(1-4) bond between the N-acetyl glucosamine and the N-acetylmuramic acid. Lipoteichoic acids may also act as receptor molecules for some Gram-positive bacteriophage; however, this has not yet been conclusively supported.It is an acidic polymer and contributes negative charge to the cell wall. Enzymes involved in the biosynthesis of WTAs have been named: TarO, TarA, TarB, TarF, TarK, and TarL. Their roles are: Following the synthesis, the ATP-binding cassette transporters (teichoic-acid-transporting ATPase) TarGH (P42953, P42954) flip the cytoplasmic complex to the external surface of the inner membrane. The redundant TagTUV enzymes link this product to the cell wall. The enzymes TarI (Q8RKI9) and TarJ (Q8RKJ0) are responsible for producing the substrates that lead to the polymer tail. Many of these proteins are located in a conserved gene cluster.