A hypothetical holoenzyme involved in the replication of the murein sacculus of Escherichia coli

• Published in: Microbiology (Society for General Microbiology) 1996-08, Vol.142 (8), p.1911-1918
• Main Author: Holtje, J.-V.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Bacteriology; Base Sequence; Biogenesis of cell structures, supramolecular organization; Biological and medical sciences; Cell Cycle; Escherichia coli; Escherichia coli - enzymology; Escherichia coli - growth & development; Escherichia coli - immunology; Fundamental and applied biological sciences. Psychology; Microbiology; Models, Structural; Molecular Sequence Data; Multienzyme Complexes - metabolism; Peptidoglycan - biosynthesis; Peptidoglycan - chemistry
• ISSN: 1350-0872; 1465-2080
• DOI: 10.1099/13500872-142-8-1911

The bag-shaped murein sacculus is a unique biopolymer consisting of glycan strands (poly-MurNAc-GlcNAc) cross-linked by short peptides. It is part of the bacterial cell wall and may be looked at as a kind of exoskeleton that endows the cell with mechanical strength and its genetically determined specific shape. The murein sacculus has to be replicated into two daughter sacculi during the cell cycle by a mechanism that guarantees maintenance of mechanical stability and shape. A hypothetical model will be presented that could explain growth and division of the stress-bearing murein sacculus of Escherichia coli by a safe and precise mechanism. It is proposed that a multienzyme complex consisting of murein hydrolases and synthases copies the existing murein sacculus that plays the role of a template. Thus, the specific shape of a bacterium may be transmitted to progeny cells by direct heritage of structural information. The rod-shaped murein sacculus of E. coli can be described as composed of a cylindrical middle part and two hemispherical polar caps. The shape of the cell is therefore defined by the diameter and the length of the cylindrical part of the rod. Whereas the length of the cell doubles in one generation, the diameter stays constant during steady-state growth. Cell division at the midpoint of the cell gives rise to two identical new rod-shaped daughter cells. Hence, a mechanism that describes the replication of the three-dimensional structure of the murein sacculus has to explain only three things. Firstly, how the diameter is kept constant, secondly, how the length is doubled in one generation, and thirdly, how the cell finds its midpoint to correctly localize cell division.