Amount of peptidoglycan in cell walls of gram-negative bacteria

Wientjes, Frans B.; Woldringh, Conrad L.; Nanninga, N.

doi:10.1128/jb.173.23.7684-7691.1991

Cited by 73 publications

(64 citation statements)

References 32 publications

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“…This means that the length of the bridge in murein must be greater than 4 nm and that the distance between the centers of adjacent glycan strands (L c ) must be greater than 5 nm because the diameter of the glycan chain is 1.1 nm (5,13). These values differ substantially from those obtained by calculation with a hypothetical peptide bridge length of 1 nm (59) that led to the conclusion that the number of layers in murein from E. coli is a little more than one (59).…”

Section: Vol 185 2003contrasting

confidence: 48%

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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Section: Vol 185 2003contrasting

confidence: 48%

Tertiary Structure of Bacterial Murein: the Scaffold Model

et al. 2003

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“…The mean sacculus surface area under the most compact conditions (pH 4.8, 1 M KCl) is 6.1 p.m2 (Table 1). This is not too different from the area for the average cell grown in rich medium (7.1 p.m2) (42,58,73).…”

Section: Resultsmentioning

confidence: 93%

Elasticity of the sacculus of Escherichia coli

1992

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Preparations of purified peptidoglycan ofEscherichia coli (i.e., sacculi) were studied by low-angle laser light scattering. Control experiments and theoretical calculations based on the Rayleigh-Gans theory showed that the mean sacculus surface area could be accurately inferred from measurements with our apparatus by using computer routines developed previously. Large changes in the mean saccular surface area resulted from alterations in the stress caused by varying the net charge on the sacculi. The net charge was affected by altering the suspending medium pH, causing carboxyl and amino groups in the peptidoglycan to gain or lose protons, or by acetylation or succinylation of the amino groups. A preponderance of either plus or minus charges caused an expansion of the mean sacculus surface area. The largest increase in area probably represents the elastic limit of the peptidoglycan and was 300%o above the area of isoionic sacculi. This degree of expansion is consistent with possible conformations of the intact peptidoglycan structure without necessitating rupture of the wall fabric. Our findings concerning saccular elasticity provide support for the surface stress theory. It provides a mechanism so that bacteria can grow and divide while maintaining turgor pressure, without the necessity of having and using proteins to do the mechanical work.It is now well established that the peptidoglycan sacculus is the stress-resistant, shape-determining structure covering the procaryotic cell (4, 23, 27-29, 34, 37, 42, 45, 46, 49, 63, 72). Its covalent structure makes the sacculus the largest macromolecule in nature and imparts strength to the bacterial wall. Additionally, the ability of the sacculus to stretch is of fundamental importance, both for giving flexibility to the organism and providing a mechanism for its enlargement during growth. The elasticity, as measured by Young's modulus, is the inverse of the ratio that a body is stretched (strain) by a given force (stress) (71). At high-enough stress, a body's elastic limit is reached, and it cannot be stretched further without the rupture of integral covalent bonds. Elastic enlargement of a single cell's wall fabric, composed of cross-linked peptidoglycan, depends on conformational changes that involve only rotations and easily made rearrangements of hydrogen bonds. Enlargement exceeding the elasticity must involve the rupture (hydrolysis in an aqueous environment) of covalent bonds (37,40).Sacculi are too small to have either their elasticity or their rupture limit (extensibility) measured by engineering materials testing methods (71). Although the sacculus cannot be affixed at two ends and mechanically stretched, the relationship between the sacculus net charge and surface area can be determined. We studied sacculi of Escherichia coli from cultures in balanced exponential growth. They were prepared free of almost all nonpeptidoglycan materials. The mean surface area of the sacculi under different conditions was measured by a low-angle laser-light-scattering method. ...

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“…Thus, the following dilemma remains: how can the apparent thickness of the murein layer as measured by electron microscopy (9, 13) be reconciled with our evidence against the inside-to-outside mode of growth that is indicative of a multilayered wall and the other cited evidence in favor of a monolayered wall (11,19)?…”

Section: Discussionmentioning

confidence: 99%

“…In contrast, a more recent article by Labischinski et al concludes, on the basis of neutron small-angle scattering studies, that the wall has "about 75-80% of its surface monolayered and 20-25% triple-layered" (11). Another recent article, by Wientjes and coworkers, argues for a monolayered wall on the basis of the diaminopimelic acid (DAP) content of the wall (19). Thus, recent evidence both for and against a multilayered sacculus in E. coli exists, although the most convincing data to me, the physical measurements of Labischinski et al, demonstrate the presence of a largely monolayered wall with some triple-layered areas (11).…”

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confidence: 84%

Turnover and recycling of the murein sacculus in oligopeptide permease-negative strains of Escherichia coli: indirect evidence for an alternative permease system and for a monolayered sacculus

Park

1993

J Bacteriol

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Turnover of murein in oligopeptide permease-negative Escherichia coli cells appeared to be minimal or nonexistent. In one strain in which it was possible to measure turnover during the first generation of chase, it was found that the rate of turnover was constant throughout a chase of three generations. This result suggests that an "inside-to-outside" mode of growth of the sacculus does not occur in E. coli. Turnover, though minimal, was significantly higher from cells labeled uniformly than from cells labeled only in the lateral wall, suggesting that a significant portion of the observed turnover is related to cell separation. Actually, turnover only appeared to be minimal in opp mutant strains. Tripeptides were being released by turnover at a rate of about 509% per generation and then were efficiently recycled. This suggests that in addition to opp, a low-affinity uptake system for tripeptide derived from the sacculus may exist.For many years, it was thought that the Escherichia coli cell wall consisted of a single layer of murein and that during growth there was little or no release of wall material. Both of these assumptions have recently been questioned. Since 1984, several lines of evidence have suggested that the murein sacculus of exponentially growing E. coli cells might be multilayered, with a thickness of up to three layers. Electron microscopic observations based on new embedding techniques and freeze substitution revealed a periplasmic space filled with an electron-dense layer of uniform thickness which was several times thicker than the peptidoglycan layer observed in previous electron micrographs (9). The authors proposed that the peptidoglycan formed a gel consisting of a cross-linked outer shell with additional lesscross-linked material attached to the inner surface. Consistent with this view was the observation that staining of thin sections of E. coli by the Rambourg technique (phosphotungstic acid in 10% chromic acid) revealed a similar 15-nmthick layer in the periplasm apparently consisting primarily of peptidoglycan (13) Holtje and Glauner have reported the presence of trimers in muramidase digests of E. coli sacculi and have suggested that this is another indication that multiple layers may exist, since a trimer cannot be present in a monolayer. These authors went on to suggest that a multilayered wall, should one exist in E. coli, ought to be formed by the "inside-tooutside" mechanism that is known to occur in gram-positive bacilli (10).In the case of Bacillus subtilis, after the murein is labeled for a short pulse and then chased, there is a lag of about one generation before any radioactivity is released into the medium. After the first generation, about 50% of the radioactivity of the cylindrical wall is released per generation (15). This is interpreted to indicate that peptidoglycan is initially laid down next to the cytoplasmic membrane and eventually reaches the external surface, where it is degraded by autolytic enzymes. Since the principal enzymes used to polymerize and cross-link...

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Amount of peptidoglycan in cell walls of gram-negative bacteria

Abstract: . 164:331-337, 1985

Cited by 73 publications

References 32 publications

Tertiary Structure of Bacterial Murein: the Scaffold Model

Tertiary Structure of Bacterial Murein: the Scaffold Model

Elasticity of the sacculus of Escherichia coli

Turnover and recycling of the murein sacculus in oligopeptide permease-negative strains of Escherichia coli: indirect evidence for an alternative permease system and for a monolayered sacculus

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