Limits...
β-Lactam formation by a non-ribosomal peptide synthetase during antibiotic biosynthesis.

Gaudelli NM, Long DH, Townsend CA - Nature (2015)

Bottom Line: Penicillins and cephalosporins are synthesized from a classically derived non-ribosomal peptide synthetase tripeptide (from δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine synthetase).We propose a mechanism, and describe supporting experiments, that is distinct from the pathways that have evolved to the three other β-lactam antibiotic families: penicillin/cephalosporins, clavams and carbapenems.These findings raise the possibility that β-lactam rings can be regio- and stereospecifically integrated into engineered peptides for application as, for example, targeted protease inactivators.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.

ABSTRACT
Non-ribosomal peptide synthetases are giant enzymes composed of modules that house repeated sets of functional domains, which select, activate and couple amino acids drawn from a pool of nearly 500 potential building blocks. The structurally and stereochemically diverse peptides generated in this manner underlie the biosynthesis of a large sector of natural products. Many of their derived metabolites are bioactive such as the antibiotics vancomycin, bacitracin, daptomycin and the β-lactam-containing penicillins, cephalosporins and nocardicins. Penicillins and cephalosporins are synthesized from a classically derived non-ribosomal peptide synthetase tripeptide (from δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine synthetase). Here we report an unprecedented non-ribosomal peptide synthetase activity that both assembles a serine-containing peptide and mediates its cyclization to the critical β-lactam ring of the nocardicin family of antibiotics. A histidine-rich condensation domain, which typically performs peptide bond formation during product assembly, also synthesizes the embedded four-membered ring. We propose a mechanism, and describe supporting experiments, that is distinct from the pathways that have evolved to the three other β-lactam antibiotic families: penicillin/cephalosporins, clavams and carbapenems. These findings raise the possibility that β-lactam rings can be regio- and stereospecifically integrated into engineered peptides for application as, for example, targeted protease inactivators.

Show MeSH

Related in: MedlinePlus

Biosynthesis of nocardicin Aa, The nocardicin NRPS contains five modules, encoded by nocA and nocB, which together activate and condense in order L-pHPG, L-Arg, D-pHPG, L-Ser and L-pHPG. The TE domain catalyses C-terminal pHPG epimerisation and hydrolysis yielding pro-nocardicin G. b, Whole-cell experiments showed nocardicin A is derived from 2 units of L-pHPG, L-Ser and S-adenosyl-L-methionine (SAM), and from nocardicin G. c, Previous experiments with excised TE demonstrate that tri- and pentapeptide thioesters containing a preformed β-lactam ring are converted to nocardicin G (R = H) and pro-nocardicin G (R = L-pHPG–L-Arg), respectively.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4401618&req=5

Figure 11: Biosynthesis of nocardicin Aa, The nocardicin NRPS contains five modules, encoded by nocA and nocB, which together activate and condense in order L-pHPG, L-Arg, D-pHPG, L-Ser and L-pHPG. The TE domain catalyses C-terminal pHPG epimerisation and hydrolysis yielding pro-nocardicin G. b, Whole-cell experiments showed nocardicin A is derived from 2 units of L-pHPG, L-Ser and S-adenosyl-L-methionine (SAM), and from nocardicin G. c, Previous experiments with excised TE demonstrate that tri- and pentapeptide thioesters containing a preformed β-lactam ring are converted to nocardicin G (R = H) and pro-nocardicin G (R = L-pHPG–L-Arg), respectively.

Mentions: Despite their widespread use for more than half a century, the β-lactam antibiotics, represented most familiarly by the semisynthetic penicillins and cephalosporins, remain the most frequently prescribed anti-infectives in human medicine.5,6 Four structurally distinct clans occur naturally, and the more recently discovered of these and their synthetic variants are of increasing importance to combat the rising specter of antibiotic resistant infectious diseases.7,8 Members of this group of antibiotics contain monocyclic and fused bicyclic β-lactams whose high energy, strained-ring skeletons are essential to their antimicrobial activities. Markedly different but chemically efficient biosynthetic pathways have evolved to each of the penicillin and cephalosporin (e.g. isopenicillin N and cephalosporin C),9 clavulanic acid10 and the carbapenem (e.g. thienamycin)11 groups (Fig. 1a and b). Ironically, the fourth and structurally simplest clan of monocyclic β-lactams, exemplified by nocardicin G (Fig. 2b), has remained an unsolved problem.12,13


β-Lactam formation by a non-ribosomal peptide synthetase during antibiotic biosynthesis.

Gaudelli NM, Long DH, Townsend CA - Nature (2015)

Biosynthesis of nocardicin Aa, The nocardicin NRPS contains five modules, encoded by nocA and nocB, which together activate and condense in order L-pHPG, L-Arg, D-pHPG, L-Ser and L-pHPG. The TE domain catalyses C-terminal pHPG epimerisation and hydrolysis yielding pro-nocardicin G. b, Whole-cell experiments showed nocardicin A is derived from 2 units of L-pHPG, L-Ser and S-adenosyl-L-methionine (SAM), and from nocardicin G. c, Previous experiments with excised TE demonstrate that tri- and pentapeptide thioesters containing a preformed β-lactam ring are converted to nocardicin G (R = H) and pro-nocardicin G (R = L-pHPG–L-Arg), respectively.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4401618&req=5

Figure 11: Biosynthesis of nocardicin Aa, The nocardicin NRPS contains five modules, encoded by nocA and nocB, which together activate and condense in order L-pHPG, L-Arg, D-pHPG, L-Ser and L-pHPG. The TE domain catalyses C-terminal pHPG epimerisation and hydrolysis yielding pro-nocardicin G. b, Whole-cell experiments showed nocardicin A is derived from 2 units of L-pHPG, L-Ser and S-adenosyl-L-methionine (SAM), and from nocardicin G. c, Previous experiments with excised TE demonstrate that tri- and pentapeptide thioesters containing a preformed β-lactam ring are converted to nocardicin G (R = H) and pro-nocardicin G (R = L-pHPG–L-Arg), respectively.
Mentions: Despite their widespread use for more than half a century, the β-lactam antibiotics, represented most familiarly by the semisynthetic penicillins and cephalosporins, remain the most frequently prescribed anti-infectives in human medicine.5,6 Four structurally distinct clans occur naturally, and the more recently discovered of these and their synthetic variants are of increasing importance to combat the rising specter of antibiotic resistant infectious diseases.7,8 Members of this group of antibiotics contain monocyclic and fused bicyclic β-lactams whose high energy, strained-ring skeletons are essential to their antimicrobial activities. Markedly different but chemically efficient biosynthetic pathways have evolved to each of the penicillin and cephalosporin (e.g. isopenicillin N and cephalosporin C),9 clavulanic acid10 and the carbapenem (e.g. thienamycin)11 groups (Fig. 1a and b). Ironically, the fourth and structurally simplest clan of monocyclic β-lactams, exemplified by nocardicin G (Fig. 2b), has remained an unsolved problem.12,13

Bottom Line: Penicillins and cephalosporins are synthesized from a classically derived non-ribosomal peptide synthetase tripeptide (from δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine synthetase).We propose a mechanism, and describe supporting experiments, that is distinct from the pathways that have evolved to the three other β-lactam antibiotic families: penicillin/cephalosporins, clavams and carbapenems.These findings raise the possibility that β-lactam rings can be regio- and stereospecifically integrated into engineered peptides for application as, for example, targeted protease inactivators.

View Article: PubMed Central - PubMed

Affiliation: Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA.

ABSTRACT
Non-ribosomal peptide synthetases are giant enzymes composed of modules that house repeated sets of functional domains, which select, activate and couple amino acids drawn from a pool of nearly 500 potential building blocks. The structurally and stereochemically diverse peptides generated in this manner underlie the biosynthesis of a large sector of natural products. Many of their derived metabolites are bioactive such as the antibiotics vancomycin, bacitracin, daptomycin and the β-lactam-containing penicillins, cephalosporins and nocardicins. Penicillins and cephalosporins are synthesized from a classically derived non-ribosomal peptide synthetase tripeptide (from δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine synthetase). Here we report an unprecedented non-ribosomal peptide synthetase activity that both assembles a serine-containing peptide and mediates its cyclization to the critical β-lactam ring of the nocardicin family of antibiotics. A histidine-rich condensation domain, which typically performs peptide bond formation during product assembly, also synthesizes the embedded four-membered ring. We propose a mechanism, and describe supporting experiments, that is distinct from the pathways that have evolved to the three other β-lactam antibiotic families: penicillin/cephalosporins, clavams and carbapenems. These findings raise the possibility that β-lactam rings can be regio- and stereospecifically integrated into engineered peptides for application as, for example, targeted protease inactivators.

Show MeSH
Related in: MedlinePlus