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Structural characterization of four prochlorosins: a novel class of lantipeptides produced by planktonic marine cyanobacteria.

Tang W, van der Donk WA - Biochemistry (2012)

Bottom Line: These polycyclic peptides contain lanthionine and methyllanthionine residues that result in thioether cross-links.All methyllanthionines had the (2S,3S,6R) configuration, and the lanthionines had the (2S,6R) configuration, irrespective of the direction of cyclization, ring size, or ring topology.These findings indicate that most, if not all, of the rings in prochlorosins are formed enzymatically by ProcM lanthionine synthetase and not by a nonenzymatic process as previously suggested.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

ABSTRACT
Prochlorosins make up a class of secondary metabolites produced by strains of Prochlorococcus, single-cell, planktonic marine cyanobacteria. These polycyclic peptides contain lanthionine and methyllanthionine residues that result in thioether cross-links. In Prochlorococcus MIT9313, a single enzyme, ProcM, catalyzes the posttranslational modification of 29 linear peptide substrates to generate a library of highly diverse cyclic peptides. To investigate the catalytic promiscuity of ProcM, we chose four prochlorosins previously demonstrated to be produced by the organism for detailed structural characterization. Nuclear magnetic resonance studies allowed unambiguous assignment of the ring topologies, demonstrating a high degree of topological diversity. The stereochemistry of the lanthionine and methyllanthionine residues was determined by gas chromatography and mass spectrometry for seven prochlorosins. All methyllanthionines had the (2S,3S,6R) configuration, and the lanthionines had the (2S,6R) configuration, irrespective of the direction of cyclization, ring size, or ring topology. These findings indicate that most, if not all, of the rings in prochlorosins are formed enzymatically by ProcM lanthionine synthetase and not by a nonenzymatic process as previously suggested.

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ll-Lan diastereomerin Pcn4.3 and its relative abundance.(A) GC–MS trace of hydrolyzed and derivatized amino acids ofPcn4.3 monitored for Lan. dd-Lan (18.2–18.6 min), dl-Lan (18.6–19.0 min), and ll-Lan (19.0–19.4min) eluted from the column, with the relative peak areas indicated.(B) 1D water-suppressed NMR spectrum of Pcn4.3. Minor peaks originatefrom a different diastereomer of Pcn4.3 containing ll-Lanas shown in panel A. Integrations of two pairs of major and minorpeaks are shown to estimate the relative amount of the diastereomer.
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fig6: ll-Lan diastereomerin Pcn4.3 and its relative abundance.(A) GC–MS trace of hydrolyzed and derivatized amino acids ofPcn4.3 monitored for Lan. dd-Lan (18.2–18.6 min), dl-Lan (18.6–19.0 min), and ll-Lan (19.0–19.4min) eluted from the column, with the relative peak areas indicated.(B) 1D water-suppressed NMR spectrum of Pcn4.3. Minor peaks originatefrom a different diastereomer of Pcn4.3 containing ll-Lanas shown in panel A. Integrations of two pairs of major and minorpeaks are shown to estimate the relative amount of the diastereomer.

Mentions: Similarly, derivatized Lan originating from Pcn1.7coeluted withthe Lan standard with the dl configuration but not with eitherthe dd or ll Lan standard (Figure 5E–G). The small shoulders on the derivatized dl-Lan peak arising from Pcn1.7 are believed to be caused by partialepimerization during HCl hydrolysis, which has been reported previously.30 The GC trace for Pcn4.3, the other prochlorosininvestigated here that contains Lan, was more complicated. Althoughthe derivatized dl-Lan was still the dominant peak, an additionalpeak in the GC trace accounted for ∼20% of the total Lan (Figure 6A). The material giving rise to this peak was confirmedto be derivatized ll-Lan by co-injections (Figure S14E ofthe Supporting Information). This resultwas in agreement with the NMR data (1D water-suppressed spectrum shownin Figure 6B), which exhibited minor peakswith integration values around 25% of that of the main peaks. TheseNMR data demonstrate that the ll-Lan was already presentin Pcn4.3 before acid hydrolysis and derivatization and was not introducedby epimerization during HCl hydrolysis.


Structural characterization of four prochlorosins: a novel class of lantipeptides produced by planktonic marine cyanobacteria.

Tang W, van der Donk WA - Biochemistry (2012)

ll-Lan diastereomerin Pcn4.3 and its relative abundance.(A) GC–MS trace of hydrolyzed and derivatized amino acids ofPcn4.3 monitored for Lan. dd-Lan (18.2–18.6 min), dl-Lan (18.6–19.0 min), and ll-Lan (19.0–19.4min) eluted from the column, with the relative peak areas indicated.(B) 1D water-suppressed NMR spectrum of Pcn4.3. Minor peaks originatefrom a different diastereomer of Pcn4.3 containing ll-Lanas shown in panel A. Integrations of two pairs of major and minorpeaks are shown to estimate the relative amount of the diastereomer.
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Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC3361976&req=5

fig6: ll-Lan diastereomerin Pcn4.3 and its relative abundance.(A) GC–MS trace of hydrolyzed and derivatized amino acids ofPcn4.3 monitored for Lan. dd-Lan (18.2–18.6 min), dl-Lan (18.6–19.0 min), and ll-Lan (19.0–19.4min) eluted from the column, with the relative peak areas indicated.(B) 1D water-suppressed NMR spectrum of Pcn4.3. Minor peaks originatefrom a different diastereomer of Pcn4.3 containing ll-Lanas shown in panel A. Integrations of two pairs of major and minorpeaks are shown to estimate the relative amount of the diastereomer.
Mentions: Similarly, derivatized Lan originating from Pcn1.7coeluted withthe Lan standard with the dl configuration but not with eitherthe dd or ll Lan standard (Figure 5E–G). The small shoulders on the derivatized dl-Lan peak arising from Pcn1.7 are believed to be caused by partialepimerization during HCl hydrolysis, which has been reported previously.30 The GC trace for Pcn4.3, the other prochlorosininvestigated here that contains Lan, was more complicated. Althoughthe derivatized dl-Lan was still the dominant peak, an additionalpeak in the GC trace accounted for ∼20% of the total Lan (Figure 6A). The material giving rise to this peak was confirmedto be derivatized ll-Lan by co-injections (Figure S14E ofthe Supporting Information). This resultwas in agreement with the NMR data (1D water-suppressed spectrum shownin Figure 6B), which exhibited minor peakswith integration values around 25% of that of the main peaks. TheseNMR data demonstrate that the ll-Lan was already presentin Pcn4.3 before acid hydrolysis and derivatization and was not introducedby epimerization during HCl hydrolysis.

Bottom Line: These polycyclic peptides contain lanthionine and methyllanthionine residues that result in thioether cross-links.All methyllanthionines had the (2S,3S,6R) configuration, and the lanthionines had the (2S,6R) configuration, irrespective of the direction of cyclization, ring size, or ring topology.These findings indicate that most, if not all, of the rings in prochlorosins are formed enzymatically by ProcM lanthionine synthetase and not by a nonenzymatic process as previously suggested.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.

ABSTRACT
Prochlorosins make up a class of secondary metabolites produced by strains of Prochlorococcus, single-cell, planktonic marine cyanobacteria. These polycyclic peptides contain lanthionine and methyllanthionine residues that result in thioether cross-links. In Prochlorococcus MIT9313, a single enzyme, ProcM, catalyzes the posttranslational modification of 29 linear peptide substrates to generate a library of highly diverse cyclic peptides. To investigate the catalytic promiscuity of ProcM, we chose four prochlorosins previously demonstrated to be produced by the organism for detailed structural characterization. Nuclear magnetic resonance studies allowed unambiguous assignment of the ring topologies, demonstrating a high degree of topological diversity. The stereochemistry of the lanthionine and methyllanthionine residues was determined by gas chromatography and mass spectrometry for seven prochlorosins. All methyllanthionines had the (2S,3S,6R) configuration, and the lanthionines had the (2S,6R) configuration, irrespective of the direction of cyclization, ring size, or ring topology. These findings indicate that most, if not all, of the rings in prochlorosins are formed enzymatically by ProcM lanthionine synthetase and not by a nonenzymatic process as previously suggested.

Show MeSH
Related in: MedlinePlus