Three-Dimensional Models of the Carbohydrate Moieties of Murein and Pseudomurein

Botanisches Institut der Universität München, Menzinger Straße 67, D-8000 München 19, Bun­ desrepublik Deutschland Z. Naturforsch. 40c, 555—561 (1985); received February 28/May 7, 1985 Carbohydrate Chain, Murein, Pseudomurein, Model Similar density values of q = 1.39— 1.46 g/cm3 and similar repeating periodicities were deter­ mined for murein and pseudomurein. Periodicities of 4.5 and 9.5 Ä were measured in the planes of the sacculi of both cell wall polymers. Vertical to these planes periodicities of 42 to 45 A were obtained. These data may be interpreted as functions of an oblique-angled elementary cell with an area of about 4.5 Ä x l O Ä and a height of 21 to 22.5 Ä. This elementary cell includes one disaccharidepeptide subunit. As a consequence of this lattice periodicities the glycan strands of murein and pseudomurein perform twofold screw axes. Therefore the peptide chains, linked at distances of about 10 Ä to every second sugar residue, point in identical directions. The parallel array of the polysaccharide chains associated with periodicities of 4.5 Ä causes, therefore, a separation of the carbohydrate and peptide moieties of murein and pseudomurein. The head-to-head or tail-to-tail packing of such layers provides periodicities of 42—45 Ä. Because of the twofold screw axis of the glycan strands, the secondary structure of the polysac­ charide strands of murein resembles the secondary structure of chitin. Since all glucosidic oxygen atoms occupy equatorial positions, if the ß-1,3 linked N-acetyl-Dglucosamine residues are in the 4C, conformation and the ß-1,3 linked N-acetyl-L-talosaminuronic acid residues in the lC4 conformation, the polysaccharide chains of pseudomurein may also perform a twofold screw axis.