Key structures of bacterial peptidoglycan and lipopolysaccharide triggering the innate immune system of higher animals: Chemical synthesis and functional studies".

Chemistry-based investigation is reviewed which led to identification of the active entities responsible for the immunostimulating potencies of peptidoglycan and lipopolysaccharide. Though these glycoconjugates which ubiquitously occur in wide range of bacteria as the essential components of their cell envelopes have long been known to enhance the immunological responses of higher animals, neither the precise chemical structures required nor the mechanism of their action had been elucidated until early 1970s. Chemical synthesis of partial structures of peptidoglycan proved N-acetylmuramyl-L-alanyl-D-isoglutamine to be the minimum structure responsible for the activity and led to later identification of its receptor protein Nod2 present in animal cells. Another active partial structure of peptidoglycan, g-D-glutamylmeso-diaminopimelic acid, and its receptor Nod1 were also identified as well. With regard to lipopolysaccharide, its glycolipid part named lipid A was purified and the structure studied. Chemically synthesized lipid A according to the newly elucidated structure exhibited full activity described for lipopolysaccharide known as endotoxin. Synthetic homogeneous lipid A and its structural analogues and labeled derivatives enabled precise studies of their interaction with receptor proteins and the mechanism of their action. Chemical synthesis of homogeneous partial structures of peptidoglycan and lipopolysaccharide gave unequivocal evidences for the concept that definite small molecular parts of these complex macromolecular bacterial glycoconjugates are specifically recognized by their respective receptors and trigger our defense system now widely recognized as innate immunity.

Key structures of bacterial peptidoglycan and lipopolysaccharide triggering the innate immune system of higher animals: chemical synthesis and functional studies.

Chemistry-based investigation is reviewed which led to identification of the active entities responsible for the immunostimulating potencies of peptidoglycan and lipopolysaccharide. Though these glycoconjugates which ubiquitously occur in wide range of bacteria as the essential components of their cell envelopes have long been known to enhance the immunological responses of higher animals, neither the precise chemical structures required nor the mechanism of their action had been [corrected] elucidated until early 1970s. Chemical synthesis of partial structures of peptidoglycan proved N-acetylmuramyl-L-alanyl-D-isoglutamine to be the minimum structure responsible for the activity and led to later identification of its receptor protein Nod2 present in animal cells. Another active partial structure of peptidoglycan, gamma-D-glutamyl-meso-diaminopimelic acid, and its receptor Nod1 were also identified as well. With regard to lipopolysaccharide, its glycolipid part named lipid A was purified and the structure studied. Chemically synthesized lipid A according to the newly elucidated structure exhibited full activity described for lipopolysaccharide known as endotoxin. Synthetic homogeneous lipid A and its structural analogues and labeled derivatives enabled precise studies of their interaction with receptor proteins and the mechanism of their action. Chemical synthesis of homogeneous partial structures of peptidoglycan and lipopolysaccharide gave unequivocal evidences for the concept that definite small molecular parts of these complex macromolecular bacterial glycoconjugates are specifically recognized by their respective receptors and trigger our defense system now widely recognized as innate immunity.

Quantitative measurement of caspase-3 activity in a living starfish egg.

If not fertilized, synchronous apoptosis is induced in starfish eggs at approximately 11h after stimulation with the hormone, 1-methyladenine. In this study, a membrane-impermeant substrate of caspase-3, acetyl-Asp-Glu-Val-Asp-coumarylamido-4-methanesulfonic acid (Ac-DEVD-CAMS), was synthesized and microinjected into a starfish egg. Caspase-3 activity in unfertilized egg was detected approximately 30min before blebbing by quantifying the accumulation rate of a membrane-impermeant, fluorogenic product, 7-aminocoumarin-4-methanesulfonic acid (ACMS), using a photomultiplier mounted on a fluorescence microscope. When active recombinant human caspase-3 was microinjected into an egg at 3h after 1-methyladenine treatment, the injected caspase-3 activity decreased and disappeared within 2h. This decrease is probably due to proteasome-dependent degradation of the enzyme, since the injected caspase-3 was degraded and a proteasome inhibitor blocked its degradation. In contrast, in aged eggs at approximately 10h after 1-methyladenine treatment, no degradation of the injected caspase-3 was observed, suggesting that endogenous caspase-3 may stabilize at this point, therefore, inducing apoptosis.