Structure of the peptidoglycan of bacterial cell walls. II

Burge, R. E.; Adams, Rachel M; Balyuzi, H. H. M.; Reaveley, D. A.

doi:10.1016/s0022-2836(77)80007-7

Cited by 50 publications

(30 citation statements)

References 27 publications

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“…While our results do not prove that stronger stresses could not result in further expansion, the sacculus reversible expansion of 300% above the released conformation area reported here is consistent with molecular models of peptidoglycan (4,5,7,44,50,51,60). While the glycan chains are quite inextensible, the peptides can have conformations varying from a compact to an extended conformation sufficient to account for a fourfold length difference and hence a 300% increase in area upon extension as well.…”

Section: Discussionsupporting

confidence: 49%

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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Section: Discussionsupporting

confidence: 49%

Elasticity of the sacculus of Escherichia coli

1992

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“…It is likely that sacculi in the earlier neutron-scattering experiments appeared multilayered because they were clumped together. Indeed, aggregated (1) and stacked sacculi (14) were frequently observed in our preparations.…”

Section: Resultsmentioning

confidence: 62%

“…Previous X-ray scattering experiments of sacculus solutions done by us (Fig. S7) and others (14) failed to reveal dominant spacings. Likewise the density tubes visualized here in tomograms were not regularly spaced or perfectly parallel (Fig.…”

Section: Resultsmentioning

confidence: 63%

Molecular organization of Gram-negative peptidoglycan

Gan¹,

Chen²,

Jensen

2008

Proc. Natl. Acad. Sci. U.S.A.

246

238

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The stress-bearing component of the bacterial cell wall-a multigigadalton bag-like molecule called the sacculus-is synthesized from peptidoglycan. Whereas the chemical composition and the 3-dimensional structure of the peptidoglycan subunit (in at least one conformation) are known, the architecture of the assembled sacculus is not. Four decades' worth of biochemical and electron microscopy experiments have resulted in two leading 3-D peptidoglycan models: ''Layered'' and ''Scaffold'', in which the glycan strands are parallel and perpendicular to the cell surface, respectively. Here we resolved the basic architecture of purified, frozenhydrated sacculi through electron cryotomography. In the Gramnegative sacculus, a single layer of glycans lie parallel to the cell surface, roughly perpendicular to the long axis of the cell, encircling the cell in a disorganized hoop-like fashion.cell wall ͉ Cryo-EM ͉ sacculus ͉ tomography ͉ cell shape T he organization of peptidoglycan within the sacculus is a longstanding question in microbiology. Although the sacculus completely envelopes the cell, protecting it from osmotic and mechanical lysis, it is also porous, and thus sieves nutrients and small proteins. Sacculi are constantly remodeled, but they are robust enough that they can be purified from cells and still retain their original shape. Early electron microscope images of purified sacculi were difficult to interpret because the images were 2-D projections through heavy metal-stained sacculi (1, 2). Nevertheless the slender appearance of peptidoglycan in thinsectioned cells (3) and the gaps perpendicular to the polar axis produced by a peptidoglycan-specific endopeptidase (4) lead to the (Circumferential) Layered model (Fig. 1A ) in which the glycan strands lie in the plane of the cell wall and wrap around the cell. The alternative Scaffold model (5) (Fig. 1B) was proposed to fit biochemical data such as pore size and crosslinkage. Various arguments have been made in favor of (6) and against (7) the Scaffold model, but the debate intensified after a recent NMR structure of a synthetic peptidoglycan subunit dimer was interpreted to support the Scaffold model (8). To gain further insight into this issue, we imaged unstained sacculi in 3-D by electron cryotomography (9). Results and DiscussionElectron Cryotomography of Purified Sacculi. Sacculi isolated from C. crescentus strain CB15N and E. coli strains MG1655 and XL-10 were vitrified across holey carbon grids in thin (Ͻ 100 nm) ice. Whereas the gossamer sacculi were barely discernable in the low-dose, 2-D projection images, they were clearly visible in the 3-D tomograms and resembled flattened cells [ Fig. 2 and supporting information (SI) Movie S1 and Movie S2]. In stark contrast to intact cells, the sacculi were flexible and in some positions had radii of curvature less than 20 nm, highlighting how cell shape is not determined by the ''rigidity'' of the sacculus, but rather the cytosolic turgor (osmotic pressure) pushing the cytoplasmic membrane outward against the sacc...

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“…2, i.e., a single-layered peptidoglycan with extended peptide chains or a partially triple layered murein, the scattering experiment described above for sacculi containing only hydrogenated peptides was repeated by using the sacculi containing deuterated peptides. In D20 suspension, the average scatteringlength density of the deuterated peptide can be estimated at approximately 5 Fig. 2).…”

mentioning

confidence: 99%

“…The neutron scattering data, indicating the existence of a partially triple layered peptidoglycan and a thickness of 2.5 to 7 nm, also help us to understand the existence of oligomeric peptidoglycan subunits as trimers and tetramers at positions other than the chain ends. If only a single-layered sacculus exists, conformational considerations require that the oligopeptides be located at the ends of the glycan because of the helical conformation of the sugar chains (5,(20)(21)(22). The partial arrangement of the peptidoglycan in more than one plane, however, is easily consistent with the experimentelly observed existence of oligomeric units within the glycan chains (22), with most of the oligopeptides located between the layers.…”

mentioning

confidence: 99%

Direct proof of a "more-than-single-layered" peptidoglycan architecture of Escherichia coli W7: a neutron small-angle scattering study

et al. 1991

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A neutron small-angle scattering study was performed to determine the thickness and the scattering density profile of isolated peptidoglycan sacculi of Escherichia coli W7 in aqueous suspension (D20). The maximum thickness (7 ± 0.5 nm) of the sacculus from the exponential-phase cells was large enough to suggest the existence of a more-than-single-layered architecture. The experimental density profile across the thickness of the sacculus did not allow an unambiguous differentiation between a single-layered architecture characterized by completely extended peptide side chains projecting from the sugar strands or, alternatively, a partially triple layered structure. To resolve this ambiguity, sacculi were labeled with deuterated wall peptides. Comparison of the two experimental profiles indicated that the sacculus is more than single layered across its surface, with about 75 to 80% of its surface single layered and 20 to 25% triple layered.

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Structure of the peptidoglycan of bacterial cell walls. II

Cited by 50 publications

References 27 publications

Elasticity of the sacculus of Escherichia coli

Elasticity of the sacculus of Escherichia coli

Molecular organization of Gram-negative peptidoglycan

Direct proof of a "more-than-single-layered" peptidoglycan architecture of Escherichia coli W7: a neutron small-angle scattering study

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