Cell wall assembly in Bacillus megaterium: incorporation of new peptidoglycan by a monomer addition process

Gally, David L.; Hancock, I.C.; Harwood, Colin R.; Archibald, A. R.

doi:10.1128/jb.173.8.2548-2555.1991

Cited by 11 publications

(11 citation statements)

References 33 publications

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“…The walls of other gram-positive bacteria exhibit a much lower degree of cross-linking, and the muropeptide fraction of these walls does not contain long oligomeric chains. For example, the walls of bacilli exhibit about 50 to 55% cross-linking, and the major component of the oligopeptide fraction is trimeric and tetrameric muropeptides (17). Furthermore, the arm lengths of the peptide antennas in the walls of other gram-positive bacteria are not as long as those in staphylococci.…”

Section: Discussionmentioning

confidence: 99%

Tertiary Structure of Staphylococcus aureus Cell Wall Murein

et al. 2004

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Staphylococcus aureus is an important human pathogen that causes life-threatening diseases including septicemia, endocarditis, toxic shock syndrome, and abscesses in organ tissues (15,25). The cell wall of the microorganism plays an important role in infectivity and pathogenicity (40). Over several decades of research, extensive knowledge has accumulated concerning epidemiology (9), virulence (25, 28), genetics (3), genomic evolution (14), the biochemistry of cell wall assembly (31), the crystal structures of ␤-lactam-resistant enzymes (24), the ultrastructure of the cell wall (4, 18), and the muropeptide composition of wild-type, methicillin-resistant (7), and vancomycinresistant strains (34). Nonetheless, the tertiary molecular structure of the cell wall, which is central for understanding cell growth and division in staphylococci, has remained elusive. As a consequence, there is no graphic illustration of the wall architecture in the literature that adequately represents known physicochemical details of staphylococcal peptidoglycan.Staphylococci are gram-positive bacteria, and their cell walls are composed of murein (32, 38, 41), teichoic acids (2), and wall-associated surface proteins (20,26,30). Stress-bearing murein represents a continuous macromolecular sacculus covering the whole cell. Murein consists of glycan strands, which are cross-linked by peptide bridges furnishing the structural integrity of the sacculus. It is a distinctive feature of staphylococci that the observed degree of murein cross-linking, which was determined as a ratio of bridged peptides to the total amount of all peptide ends in general, is extremely high, on the order of 80 to 90% (16, 35).Glycan strands in staphylococcal murein are composed of N-acetylglucosamine (GlcpNAc) and N-acetylmuramic acid (MurpNAc) residues that furnish ␤-(134)-linked disaccharide repeating units, with MurpNAc representing the reducing terminus of the chain. The carboxyl group of each MurpNAc residue is amidated by the stem pentapeptide L-Ala-D-isoGln-L-Lys-D-Ala-D-Ala, and the ε-amino group of the lysine residue is substituted with a pentaglycine appendage (37). Thus, each peptide attached to a MurpNAc residue is a branched decapeptide with an amino group on the Gly and a carboxyl group on the D-Ala terminus, and arms of the peptide side chains interact with each other to provide a high degree of murein cross-linking. Although the general principle of murein structural organization is simple, the muropeptide composition of the staphylococcal sacculi appears very complex, as a standard digestion of sacculi with muramidase (the enzyme that cleaves MurpNAc glycosidic bonds) releases more than 20 distinct components plus an unresolved material. The latter makes up about 50 to 60% of the muropeptide-containing oligomers, with up to 20 repeating units (7,38). Thus, the major part of staphylococcal murein architecture could be envisaged as being constructed of interlinked glycan and oligopeptide chains, both varying in their lengths.On electron micrographs, the ...

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Section: Discussionmentioning

confidence: 99%

Tertiary Structure of Staphylococcus aureus Cell Wall Murein

et al. 2004

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“…The box possessed 625 positions at which to insert randomly selected strands and was bordered at the bottom and at the top by the inner and outer membranes (the latter being absent from gram-positive envelopes), respectively. Importantly, the box was flanked along the perimeter by the existing murein fabric to allow incoming strands to crosslink with it and to bring the simulated process of matrix assembly into agreement with the murein assembly process in vivo (15,16,22,55). The height of the box, i.e., the thickness of the matrix, was estimated to be about 30 disaccharide units, which allowed it to hold all of the strands that were present in the strand pool (see Appendix).…”

Section: Vol 185 2003mentioning

confidence: 99%

“…In the published computer simulations of the planar murein network, the cutting approach that was used contradicts the general biological principle of sequential chain attachment (15,16,22,55). A functional, i.e., stable, network could only be created under the condition of a maximal degree of crosslinking.…”

Section: Vol 185 2003mentioning

confidence: 99%

“…(i) Assumptions. In agreement with the general principle of murein biogenesis in vivo, the assembly process in silico should proceed via sequential attachment of the growing nascent peptidoglycan strands to the existing murein fabric (15,16,22,55). Other investigators have noted that a computer simulation of a planar murein network assembled by this mechanism is rather prob- One tessera and the sample aggregate of two tesserae are shown in gray.…”

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Tertiary Structure of Bacterial Murein: the Scaffold Model

et al. 2003

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parallel orientation with respect to the plasma membrane. However, after integrating published experimental data on glycan chain length distribution and the degree of peptide side chain cross-linking into this computer simulation, we now report that the proposed planar network of murein appears largely dysfunctional. In contrast, a scaffold model of murein architecture, which assumes that glycan strands extend perpendicularly to the plasma membrane, was found to accommodate published experimental evidence and yield a viable stress-bearing matrix. Moreover, this model is in accordance with the wellestablished principle of murein assembly in vivo, i.e., sequential attachment of strands to the preexisting structure. For the first time, the phenomenon of division plane alternation in dividing bacteria can be reconciled with a computer model of the molecular architecture of murein.The biological role, chemical structure, physical properties, and principles of biogenesis of cell walls of both gram-positive and gram-negative bacteria have been extensively reviewed since the mid-1960s (1, 8, 17-19, 26, 29, 33, 44, 51, 53, 56, 57). The major structural component of all types of bacterial walls is murein, the terms murein and peptidoglycan being synonymous. Although its composition and fine chemical structure vary in different bacteria (52), the general principle of its structural organization holds constant. The material, regardless of the bacterial cell morphology and the wall thickness, is invariably composed of peptidoglycan strands cross-linked via peptide bridges. Other polymers that are associated with the sacculus in different bacteria (teichoic acids, lipoteichoic acids, polysaccharides, proteins, and lipoproteins) are not essential to the mechanical firmness of murein and, therefore, are not further discussed here.To date, the crucial question of how the three-dimensional organization of murein can be visualized remains unanswered. Since there is no methodology that allows investigation of the architecture of murein in intact cells, researchers have had to deduce the tertiary structure on the basis of indirect evidence, the unambiguous interpretation of which is often difficult.Currently, three models of the architecture of murein are discussed in the literature. (i) The predominant concept considers the peptidoglycan strands to run regularly and in parallel with the plasma membrane, furnishing a planar network (8,29). (ii) An analogous model assumes an irregular orientation of peptidoglycan strands in the planar network (33,34). (iii) The scaffold model proposes that peptidoglycan strands are oriented perpendicular to the plasma membrane (12, 13). The radial orientation of glycan strands within bacterial walls was hypothetically contemplated but rejected by Keleman and Rogers (32). It is important to note that the planar network models consider the thin gram-negative cell walls to consist of one major stress-bearing layer in combination with newly synthesized (innermost) and almost degraded (outermost) loosely...

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“…We have noted (Gally, 1991 ;Gally et al, 1991) that these conditions are unlikely to be met during peptido-glycan assembly in Gram-positive bacteria. The thickness of the wall in these bacteria is such that peptides in the outer regions will not be accessible at the wall-membrane interface where new material is incorporated.…”

Section: Introductionmentioning

confidence: 99%

Cell wall assembly in Staphylococcus aureus: proposed absence of secondary crosslinking reactions

Gally

1993

Journal of General Microbiology

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The distribution of muropeptides formed by muramidase digestion of peptidoglycan from Staphylococcus aureus H was determined by gel-filtration HPLC. The observed crosslinking pattern supports the conclusion that incorporation of peptidoglycan in S. aureus proceeds by a similar mechanism to that proposed earlier for Bacillus megaterium. In this mechanism single glycarepeptide strands are incorporated into the sacculus by crosslinking reactions that take place only between the monomer muropeptide units of the incoming glycopeptide and muropeptides present in the innermost region of wall at the wall-membrane interface : such crosslinking reactions take place only during incorporation and no other crosslinking reactions occur. This assembly process has now been termed restricted monomer addition. The present analysis shows that the distribution of muropeptides in S. aureus peptidoglycan is in excellent agreement with that predicted by this mechanism. We propose that cell wall assembly in S. aureus proceeds via restricted monomer addition without any requirement for the secondary crosslinking reactions that have been suggested to occur in this organism. The high degree of crosslinking in S. aureus, 80% in this study, may result mainly from the freedom for crosslinking provided by the pentaglycine bridge peptide.

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Cell wall assembly in Bacillus megaterium: incorporation of new peptidoglycan by a monomer addition process

Cited by 11 publications

References 33 publications

Tertiary Structure of Staphylococcus aureus Cell Wall Murein

Tertiary Structure of Staphylococcus aureus Cell Wall Murein

Tertiary Structure of Bacterial Murein: the Scaffold Model

Cell wall assembly in Staphylococcus aureus: proposed absence of secondary crosslinking reactions

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