Enzymes enzyme modifications from modified genes

The activity of PK and NRPSs is often precluded and/or followed by actions upon the natural products by modifying enzymes. There exists a first level of diversity in which the monomers for respective synthases must be created. For instance, in the case of many NRPs, noncanonical amino acids must be biosynthesized by a series of enzymes found within the biosynthetic gene cluster in order for the peptides to be available for elongation by the NRPS. A second level of molecular diversity comes into play via post-synthase modification. Examples of these activities include macrocyclization, heterocyclization, aromatization, methylation, oxidation, reduction, halogenation, and glycosylation. Finally, a third level of diversity can occur in which molecules from disparate secondary metabolic pathways may interact, such as the modification of a natural product by an isoprenoid oligomer. Here, we will cover only a small subsection of... 

The lantibiotics differ extensively from the class II bacteriocins in that they contain post-translationally modified amino acids, as for example dehydrated amino acids and lanthionine residues, forming intramolecular thioether bridges [39, 184]. The chemical modification reactions leading to the typical lanthionines were first proposed by Ingram [185] and are assumed to be catalyzed by specific enzymes encoded in the lantibiotic gene cluster. In the lantibiotic lactocin S, p-alanine residues were discovered, probably by conversion of dehydrated serine residues via a dehydrogenation reaction [82]. In some... 

Post-translational modifications, such as phosphorylation, complex glycosylation, and lipidation, typically occur in eukaryotic organisms. Therefore, their expression in prokaryotic systems like Escherichia coli is difficult. However, it should be noted that via clever engineering and coexpression of specific enzymes, access can be granted to specific lipidated proteins via expression in bacteria, for example, via the expression of A -myristoyltransferase in E. coli Eukaryotic systems that can be used for the expression of post-translationally modified proteins are yeast and Dictyostelium discoidum. Furthermore, lipidated proteins, such as the Rah proteins, can be obtained via purification from tissue sources or from membrane fractions of insect cells that had been infected with baculovirus bearing a Rah gene. ... 

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