A Three‐Dimensional Atomic Model of the Murein Layer of Bacteria

Abstract

X‐Ray diffraction, infrared spectra and density of murein, the rigid component of almost all bacterial cell walls, were measured using gram‐negative (Spirillum serpens) and gram‐positive (Lactobacillus plantarum) strains. X‐Ray diffraction of dried foils of murein showed Debye‐Scherrer rings, indicating periodicities of 0.93 to 1.00 and 0.44 nm. The comparison of the infrared spectra of chitin and murein showed that their amide I and amide II bands have the same frequencies. With isopycnic density‐gradient centrifugation of murein a density of ϱ= 1.46 g × cm−3 was observed. Based on these data, on theoretical considerations and on model building the following structure of murein is proposed: the structure of the glycan chains in murein is similar to that of chitin and cellulose. The peptides consisting of alternating d‐ and l‐amino acids have the 2.27 helical conformation. They are linked to the carbohydrate chains through their N‐terminus and form two hydrogen bonds with the sugar residues. This linkage causes an angle of about 150° between the carbohydrate and peptide chains. Copyright © 1974, Wiley Blackwell. All rights reserved