Peptidoglycan types of bacterial cell walls and their taxonomic implications.

Cholesterol and the cell membrane.

Membranes are the most common cellular structures in both plants and animals. They are now recognized as being involved in almost all aspects of cellular activity ranging from motility and food entrapment in simple unicellular organisms, to energy transduction, immunorecognition, nerve conduction and biosynthesis in plants and higher organisms. This functional diversity is reflected in the wide variety of lipids and particularly of proteins that compose different membranes. An understanding of the physical principles that govern the molecular organization of membranes is essential for an understanding of their physiological roles since structure and function are much more interdependent in membranes than in, say, simple chemical reactions in solution. We must recognize, however, that the word ‘understanding’ means different things in different disciplines, and nowhere is this more apparent than in this multidisciplinary area where biology, chemistry and physics meet.

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Physical principles of membrane organization.

The description of membrane lipid conformation, order and dynamics by 2H-NMR

The motivation for this review arises from the conviction that, as a result of the mass of experimental data and observations collected in recent years, the study of the physical properties of membranes is now entering a new stage of development. More and more, experiments are being designed to answer specific, detailed questions about membranes which will lead to a quantitative understanding of the way in which the physical properties of membranes are related to and influence their biological function.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033583500003735

Physical properties of the fluid lipid-bilayer component of cell membranes: a perspective.

THE most convincing studies of molecular order in model membranes are undoubtedly those involving deuterium nuclear magnetic resonance (NMR) of labelled lipids in the lamellar liquid crystalline phase1–6. The relevance of these results to biological membranes has not yet been established, however; there is no a priori reason to expect the state of organisation of lipids in the lamellar liquid crystal to resemble closely that of a natural membrane. We report here the first detailed study of acyl chain order in the lipids of a natural biological membrane—the plasma membrane of the microorganism Acholeplasma laidlawii. Specifically deuterated fatty acids were incorporated biosynthetically into the membrane lipids as described previously7. The 2H-NMR spectra of the membrane demonstrate the co-existence of at least two different kinds of lipid. Signals from the more fluid lipid are most prominent at temperatures near and above the growth temperature (37 °C). The more solid-like lipid, which predominates at lower temperatures, may be similar to the gel state of lamellar phases and could include lipid associated with the membrane protein. For the more fluid phase, the plot of order parameter against position of deuteration strongly resembles that for egg yolk2 and dipalmitoyl3 phosphatidylcholine. Incorporation of cholesterol into the membrane of A. laidlawii increases the average acyl chain order and also increases the spread of order parameters, similar to its effect on egg yolk phosphatidylcholine6. These results represent a major justification for the use of lamellar liquid crystals as models for the lipid in biological membranes.

Deuterium NMR study of lipid organisation in Acholeplasma laidlawii membranes

The structure of an R-type oligosaccharide core obtained from some lipopolysaccharides of Neisseria meningitidis.

/pdf/penicillin-sensitive-dd-carboxypeptidases-from-streptomyces-285f5xfbdl.pdf

Penicillin-sensitive DD-carboxypeptidases from Streptomyces strains R39 and K11.

In the presence of Nα,Ne-diacetyl-L-Lys-D-Ala-D-Ala as donor, and either D-[14C]alanine, [14C]-glycine, or meso-[3H]diaminopimelic acid as acceptor, the DD carboxypeptidases from Streptomyces R61 and R39 catalyze a transpeptidation reaction with the release of terminal D-alanine from the donor and the formation of either Nα,Ne-diacetyl-L-Lys-D-Ala-D-[14C]Ala, Nα,Ne-diacetyl-L-Lys-D-Ala-[14C] Gly, or Nα,Ne-diacetyl-L-Lys-D-Ala-D-meso- [3H]diaminopimelic acid. The reaction appears to be a true transpeptidation, and is not simply a “reversal of hydrolysis”. Transpeptidation is inhibited by pencillin at concentrations that inhibit hydrolysis (carboxypeptidase action) of the donor peptide. There are differences in the specificity profiles of the Streptomyces enzymes for acceptor molecules:only the R61 enzyme used [14C]Gly-Gly as acceptor; transfer of Nα,Ne-diacetyl-L-Lys-D-Ala to this acceptor resulted in the formation of Nα,Ne-diacetyl-Lys-D-Ala-[14C] Gly-Gly, with the synthesis of a (D-Ala-Gly) peptide bond in an endoposition.

https://www.pnas.org/content/pnas/69/3/662.full.pdf

Kenneth G. Johnson

Papers

Deuterium NMR study of lipid organisation in Acholeplasma laidlawii membranes

The structure of an R-type oligosaccharide core obtained from some lipopolysaccharides of Neisseria meningitidis.

Penicillin-sensitive DD-carboxypeptidases from Streptomyces strains R39 and K11.

Transpeptidase Activity of Streptomyces D-Alanyl-D Carboxypeptidases

Structure of the 3-deoxy-d-manno-octulosonic acid-containing polysaccharide (K6 antigen) from escherichia coli LP 1092