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Peptide antibiotics are classified according to their overall shape, which can be linear or cyclic, and by the nature of the bonds joining the constituent amino acids and other carboxylic acids, which can be all amide bonds or amide plus ester bonds. Most peptide antibiotics are cyclic peptides that do not contain disulfide linkages. Peptide antibiotics differ in many respects from proteins. The vast majority of peptide antibiotics have molecular weights in the 500–1500 range, whereas the average protein has a mol wt of 40,000. Many peptide antibiotics have unusual fatty acids and amino acids, such as D ‐amino acids, N ‐methyl amino acids, or imino acids, and they usually lack methionine and histidine. Ring closure in cyclic peptide antibiotics is by amide or ester bonds. Peptide antibiotics are normally resistant to the usual proteases and peptidases. They are usually synthesized on multienzyme complexes much as are fatty acids, and not on ribosomes as are proteins. Most peptide antibiotics are synthesized as groups of closely related structures. Even the small fraction of peptide antibiotics that have therapeutic usefulness are quite toxic. The ratio of the minimum toxic dose to the maximum effective dose is smaller than for most nonpeptide antibiotics. Peptide antibiotics are not often the drugs of first choice for systemic therapy of important human disease. However, the World Health Organization, which chooses drugs especially for Third World use based on efficacy, safety, quality, price, and availability, includes such peptide antibiotics as bleomycin, dactinomycin, and bacitracin, plus several β‐lactams. The complex structure of peptide antibiotics adds considerably to the problems of synthesis, but more recent efforts toward improved peptide antibiotics are encouraging.
Peptide antibiotics are classified according to their overall shape, which can be linear or cyclic, and by the nature of the bonds joining the constituent amino acids and other carboxylic acids, which can be all amide bonds or amide plus ester bonds. Most peptide antibiotics are cyclic peptides that do not contain disulfide linkages. Peptide antibiotics differ in many respects from proteins. The vast majority of peptide antibiotics have molecular weights in the 500–1500 range, whereas the average protein has a mol wt of 40,000. Many peptide antibiotics have unusual fatty acids and amino acids, such as D ‐amino acids, N ‐methyl amino acids, or imino acids, and they usually lack methionine and histidine. Ring closure in cyclic peptide antibiotics is by amide or ester bonds. Peptide antibiotics are normally resistant to the usual proteases and peptidases. They are usually synthesized on multienzyme complexes much as are fatty acids, and not on ribosomes as are proteins. Most peptide antibiotics are synthesized as groups of closely related structures. Even the small fraction of peptide antibiotics that have therapeutic usefulness are quite toxic. The ratio of the minimum toxic dose to the maximum effective dose is smaller than for most nonpeptide antibiotics. Peptide antibiotics are not often the drugs of first choice for systemic therapy of important human disease. However, the World Health Organization, which chooses drugs especially for Third World use based on efficacy, safety, quality, price, and availability, includes such peptide antibiotics as bleomycin, dactinomycin, and bacitracin, plus several β‐lactams. The complex structure of peptide antibiotics adds considerably to the problems of synthesis, but more recent efforts toward improved peptide antibiotics are encouraging.
The proton nmr spectra of bacitracin A in H2O and DMSO-d6 have been assigned and the conformational behavior of the peptide in the two solvents has been compared. Although bacitracin A shows a conformational equilibrium between at least two conformations differing in the relative position of the cyclic and linear domains of the molecule, the spectra in water can be interpreted in terms of a preferred conformation in which the linear part is folded over the cyclic moiety and a turn is present around Ile(8)-DPhe(9).
Archaea was until recently considered as a third domain of life in addition to bacteria and eukarya but recent studies support the existence of only two superphyla (bacteria and archaea). The fundamental differences between archaeal, bacterial, and eukaryal cells are probably the main reasons for the comparatively lower susceptibility of archaeal strains to current antimicrobial agents. The possible emerging pathogenicity of archaea and the role of archaeal methanogens in methane emissions, a potent greenhouse gas, has led many researchers to examine the sensitivity patterns of archaea and make attempts to find agents that have significant anti-archaeal activity. Even though antimicrobial peptides (AMPs) are well known with several published reviews concerning their mode of action against bacteria and eukarya, to our knowledge, to date no reviews are available that focus on the action of these peptides against archaea. Herein, we present a review on all the peptides that have been tested against archaea. In addition, in an attempt to shed more light on possible future work that needs to be performed we have included a brief overview of the chemical characteristics, spectrum of activity, and the known mechanism of action of each of these peptides against bacteria and/or fungi. We also discuss the nature of and key physiological differences between Archaea, Bacteria, and Eukarya that are relevant to the development of anti-archaeal peptides. Despite our relatively limited knowledge about archaea, available data suggest that AMPs have an even broader spectrum of activity than currently recognized.
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