Synth Pro9

Lipid A biosynthesis initiates by acylation of UDP-GlcNAc at C3, followed by N-deacetylation, N-acylation, and cleavage of the pyrophosphate linkage to form 2,3 diacylglucosamine-1-phosphate. This can condense with another molecule of UDP-diacylglucosamine to form the tetraacyl disaccharide core. A 4′ kinase phosphorylates the nonreducing sugar and then KDO transferases initiate the formation of the core region. Interestingly, the other two β-hydroxyl-linked fatty acids are added only after the KDO units are added. The formation of KDO2lipid A is essential for survival of E. coli, but this might not be true for all gram-negative bacteria. Deep rough mutants of E. coli and Salmonella lack the core and outer chains but contain a KDO-bearing lipid A. The assembly process occurs in the inner membrane, but very little is known about the translocation of lipid A to the outer leaflet of the outer membrane.

Figure 21.7. Structure of heptose and KDO. LPS contains several unusual sugars not found in vertebrates.

After assembly of lipid A, the inner core regions of heptoses, hexoses, and phosphate groups are added. A large number of genes encoding various transferases (clustered in the rfa locus) participate in this process. The biosynthesis of the outer Oantigens occurs independently of lipid A and the inner core and utilizes activated nucleotide sugars and undecaprenyl-phosphate. Apparently, the chain grows from the reducing terminus while attached to the carrier. When outer chain synthesis is completed, it is transferred en bloc to the core region of LPS. The assembly process occurs by membrane-bound enzymes facing the cytosol, but the ligation to the inner core is thought to occur in the periplasm.

The O-antigens consist of two to eight sugars, repeated ≤50 times. A broad range of sugars are present, including free and amidated uronic acids, amino sugars, methylated and deoxygenated derivatives, acetylated sugars, and others containing covalently bound amino acids and phosphate. The Oantigens, as their name implies, define various serotypes distinguished by their reactivity with human antisera. More than 170 serotypes of E. coli are known. No strict correlation exists between serotypes and disease, although some infections are more typical of certain serotypes. From the bacterium's point of view, the O-antigen probably provides a hydrophilic barrier to hydrophobic antibiotics (natural fungal and bacterial metabolites), bile acids (in enterobacteria), and complement.

Escherichia coli Mutants Lacking All Possible Combinations of Eight Penicillin Binding Proteins: Viability, Characteristics, and Implications for Peptidoglycan Synthesis To better understand the contributions these proteins make to the physiology of Escherichia coli, we constructed 192 mutants from which eight PBP genes were deleted in every possible combination.

Components of the outer membrane are synthesized at the plasma membrane  but the mechanism whereby they are incorporated in controlled fashion is not  under­stood. One of the components of the outer membrane is a regularly arranged surface protein. The synthesis and turnover of this protein is considered in particular detail in this  paper. The characteristics of its formation provide  a mechanism whereby the cell is always  completely covered with surface protein. This indicates that the surface protein has an important biological function.

Synthesis and Turnover of the Regularly Arranged Surface Protein of Acinetobacter sp. Relative to the Other Components of the Cell Envelope KAREEN J. I. THORNE,* RHONDA C. OLIVER, AND AUDREY M. GLAUERT Strangeways Research Laboratory, Worts Causeway, Cambridge CB1  4RN, United Kingdom Received for publication 7 April 1976 The formation of the components of the cell envelope  ofAcinetobacter sp. 199A was investigated by measuring the incorporation of [3H]leucine  into protein, [14C]galactose into lipopolysaccharide, 32P into phospholipid, and  [3H]dia­minopimelic acid into peptidoglycan. Whereas the lipopolysaccharide and intrinsic protein of the outer membrane were stable, some of the  regularly arranged surface protein, the a­protein, was lost into the growth  medium. Only newly synthesized a­protein was lost. The peptidoglycan of the  murein layer was also labile. Selective inhibition of the formation of  individual components of the cell envelope with penicillin, chloramphenicol, and bacitracin  showed that incorporation of protein into the outer membrane required the  simultaneous

Hartmann E, Konig H. Angewandte Mikrobiologie, Universitat Ulm, Germany. The peptide subunits of the pseudomurein, the cell-wall peptidoglycan of some methanogens, are usually composed of glutamic acid, alanine and lysine. In order to get a more detailed picture of the biosynthetic pathway of the peptide subunit, we performed in vitro assays. Starting from glutamic acid a pentapeptide was obtained in seven steps: [formula: see text] The pentapeptide structure was identical to that of the peptide subunit of the intact pseudomurein except one additional alanine residue, which is split off during further processing. The pentapeptide synthesis starts with glutamic acid, which is phosphorylated at the N alpha-amino group. N alpha-phosphoryl-glutamic acid is transferred to a nucleotidecarrier, forming N alpha-UDP-glutamic acid. The further pentapeptide biosynthesis is achieved via a di-, tri- and tetrapeptide by stepwise addition of the corresponding amino acids.