A large family of cytotoxic cyclic peptides exemplified by the patellamides has been isolated from ascidians harboring the obligate cyanobacterial symbionts Prochloron spp.. Genome sequence analysis of these symbionts has revealed that Prochloron spp. synthesize patellamides by a ribosomal pathway. To understand how this pathway evolved to produce a suite of related metabolites, we analyzed 46 prochloron-containing ascidians from the tropical Pacific Ocean for the presence of patellamide biosynthetic genes and taxonomic markers. Here, we show that Prochloron spp. generate a diverse library of patellamides using small, hypervariable cassettes within a conserved genetic background. Each symbiont strain contains a single pathway, and mixtures of symbionts within ascidians lead to the accumulation of chemical libraries. We used this information to engineer the production of a new cyclic peptide in Escherichia coli, thereby demonstrating the power of comparative analysis of closely related symbiotic pathways to direct the genetic synthesis of new molecules.
Small, N-C terminally cyclic ribosomal peptides are common in nature, yet the mechanisms underlying their biosyntheses remain largely unknown. We recently identified candidate peptide cyclase genes in the metagenomes of marine animals. Here we report that PatG, a protease discovered in this analysis, cleaves variables, short peptides out of a precursor protein and cyclizes these peptides in vivo and in vitro.
The infrared spectra of some hydrated transition-metal perchlorates, some transition-metal perchlorate-methyl cyanide complexes, and anhydrous copper perchlorate are reported. The spectra are interpreted in terms of ionic perchlorate and perchlorato-groups.As a result of the observation that anhydrous cupric perchlorate is volatile the infrared spectrum of this and some transition-metal perchlorate complexes have been examined to obtain evidence of the formation of the metal-perchlorate bond in the solid state.The infrared spectra of a number of ionic perchlorates are listed by Miller and The Raman spectrum of the perchlorate ion has been studied by several investigator^,^*^ and apart from minor differences in the numerical values accepted for its fundamentals their assignments have been established. The perchlorate ion has a regular tetrahedral structure and belongs to the point group T d , having nine vibrational degrees of freedom distributed between four normal modes of vibration. The assignments of these modes are listed in Table 1. I n general the triply degenerate frequencies v3 and v4 are observed TABLE 1. Vibrations of the C10, group as a function of symmetry.?
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