No abstract

Using the known mapping position the gene encoding a ␤-1,4-N-acetylglucosaminidase needed for the degradation of muropeptides could be identified. nagZ encodes a cytosolic enzyme active on N-actylglucosamyl-␤-1,4-(1,6)-anhydromuramic acid containing muropeptides. These degradation products of the peptidoglycan are formed during the enlargement of the murein sacculus as a consequence of a growth mechanism, which couples the controlled degradation of the cell wall polymer with the insertion of new material. NagZ is needed for the formation of monosaccharides from the released disaccharides during the cytosolic steps of the muropeptide-recycling pathway. The formation of intracellular 1,6-anhydro-N-acetylmuramyl-peptides is important for the expression control of the inducible ␤-lactamases of the AmpC type. A mutant lacking active NagZ cannot establish AmpC mediated ␤-lactam resistance. The biochemical characterization of the enzyme showed its activity on different muropeptides and inhibitors of enzyme activity could be identified. This observation might be important for designing inhibitors of NagZ that could prevent the establishment of ␤-lactam resistance of Enterobacteria possessing inducible ␤-lactamases.Bacteria are enclosed by an exoskeletal structure found in the cell envelope (1). In most cases the bag-shaped macromolecule murein (peptidoglycan) stabilizes the cell mechanically and determines the shape of the bacterium (2). It is a heteropolymer, made up of glycan strands composed of an alternating sequence of two amino-sugars (N-acetylmuramic acid and Nacetylglucosamine) linked by ␤-1,4 glycosidic bonds (reviewed by Höltje in Ref.3). The glycans are interlinked by short peptide bridges, and a covalently closed network completely surrounding the cell is formed. To enlarge this structure not only does new material have to be synthesized, it has to be integrated into the existing murein. This is accomplished by the concerted action of murein synthases and murein hydrolases (3-6). During the controlled enlargement of the exoskeleton, old material from the sacculus gets released as turnover products while the polymer grows by the insertion of new murein glycan strands (7-9). Different enzymatic activities have been described to take part in this turning over of the murein sacculus. Lytic transglycosylases are muramidases that are degrading the glycan strands to anhydro-disaccharides (10), endopeptidases cleave peptide cross-links (11-13) and N-acetylmuramyl-L-alanine amidases release oligopeptides from the murein or from muropeptides (7). As a result of the action of these enzymes, disaccharides (N-acetylglucosamyl-␤-1,4-(1,6)-anhydro-N-acetylmuramic acid) are formed that carry a characteristic 1,6-anhydro ring structure at the muramic acid.For Escherichia coli the turnover process has been well studied, and it could been shown that during one generation up to 50% of the cell wall gets degraded as a result of normal growth processes (9, 14). These breakdown products are efficiently reutilized by E. coli in a r...

Design of attachment devices in insects varies enormously in relation to different functional loads. Many systems, located on different parts of the body, involve surfaces with particular frictional properties. Such systems evolved to attach parts of the body to each other, or to attach an insect to the substratum by providing fast and reversible attachment/detachment. Among these systems, there are some that deal with predefined surfaces, and others, in which one surface remains unpredictable. The first type of system occurs, for example, in wing-locking devices and head-arresting systems and is called probabilistic fasteners. The second type is mainly represented by insect attachment pads of two alternative designs: hairy and smooth. The relationship between surface patterns and/or mechanical properties of materials of contact pairs results in two main working principles of the frictional devices: mechanical interlocking, or maximization of the contact area. We give an overview of the functional design of two main groups of friction-based attachment devices in insects: probabilistic fasteners and attachment pads.