Patellamide A and C biosynthesis by a microcin-like pathway inProchloron didemni, the cyanobacterial symbiont ofLissoclinum patella

Abstract

Prochloron spp. are obligate cyanobacterial symbionts of many didemnid family ascidians. It has been proposed that the cyclic peptides of the patellamide class found in didemnid extracts are synthesized by Prochloron spp., but studies in which host and symbiont cells are separated and chemically analyzed to identify the biosynthetic source have yielded inconclusive results. As part of the Prochloron didemni sequencing project, we identified patellamide biosynthetic genes and confirmed their function by heterologous expression of the whole pathway in Escherichia coli. The primary sequence of patellamides A and C is encoded on a single ORF that resembles a precursor peptide. We propose that this prepatellamide is heterocyclized to form thiazole and oxazoline rings, and the peptide is cleaved to yield the two cyclic patellamides, A and C. This work represents the full sequencing and functional expression of a marine natural-product pathway from an obligate symbiont. In addition, a related cluster was identified in Trichodesmium erythraeum IMS101, an important bloom-forming cyanobacterium.heterocycle ͉ tunicate ͉ ascidian ͉ genome sequencing ͉ lantibiotic

Spontaneity in the patellamide biosynthetic pathway

“…Repeating essentially the autoannotation of Schmidt et al, 6 a search of the whole Pfam HMM library with each protein sequence of seven Prochloron didemni genes did not show the presence of additional adenylation, epimerisation, racemisation or cyclisation domains other than those shown in the sequence description. The highest scores and most relevant results were obtained with peptidase S8 from the subtilase family found in patA subtilisin-like protein and as a part of patG thiazoline oxidase/subtilisin-like protease and the YcaO from YcaO-like family found in the patD adenylation/heterocyclisation protein (identified by match to protein families HMM PF00082 and HMM PF02624).…”

“…4 L. patella contains an as yet uncultured primitive photosynthetic prokaryote Prochloron didemni, which is closely related to the cyanobacteria, but differs in the fact that it possesses both chlorophylls a and b, lacks phycobilins and has plant-like thylakoids. 5 Recent work has indicated that the patellamides are unprecedented examples of post-translationally modified ribosomal peptides, 6 produced by the Prochloron didemni symbiont. 7 The patellamides are the most complex examples of this unusual family of peptides which includes the lantibiotics 8 and microcins, 4 as they contain a unique combination of heterocycles (cf microcin B17), 4 a macrocycle (cf microcin J25) 9 and D stereocentres.…”

“…In addition, the same gene encodes two different products. The gene cluster shows extremely low sequence homology to genes of known function, 6 indicating that the pathway might contain novel enzymes. In addition, the heterocyclisation of dipeptides (XC, XT, XS) to give thiazole and oxazoline rings appears to be more tolerant to changes at X 10 than that observed in microcin B17, indicating that this process might be exploitable for biotechnological applications such as the combinatorial biosynthesis of novel bioactive products and semi-synthetics.…”

Construction of soil environmental DNA cosmid libraries and screening for clones that produce biologically active small molecules

“…Even though most bacteria are not readily cultured in the laboratory, it is possible to extract microbial DNA directly from the naturally occurring consortia of bacteria present in environmental samples (environmental DNA (eDNA)). Introduction of this previously inaccessible genetic material into easily cultured bacterial hosts provides one means to access the biosynthetic potential of uncultured bacteria [3][4][5][6][7][8][9][10][11][12][13] . Culture-independent analysis of the genetic and biochemical diversity present in naturally occurring bacterial communities, which began in the 1990s (see refs.…”

Accessing chemical diversity from the uncultivated symbionts of small marine animals

“…However, only two examples employing this strategy exist, one involving marine animals, 4 and the other the uncultivated human microbiota, 5,6 leaving substantial hurdles to accessing chemical novelty. Collectively, such systems feature hundreds or thousands of biosynthetic pathways to bioactive compounds, only a few of which have been accessed.…”