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Category: Bacterial Pathogenesis
Enzymatic Assembly Lines for Nonribosomal Peptide Antibiotics, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817886/9781555818937_Chap13-1.gif /docserver/preview/fulltext/10.1128/9781555817886/9781555818937_Chap13-2.gifAbstract:
A large percentage of the peptidic natural products that have antibiotic activity are produced by nonribosomal peptide synthetases (NRPSs). The NRPSs catalysts have organizational analogies to the type I polyketide synthases (PKSs) as multidomainal catalysts organized into modules, with multiple modules collected in one or more protein subunits. These include the L-aminoadipyl-L-cysteinyl-D-valine (ACV) tripeptide precursor to the β-lactam families of antibiotics, the channel-forming tyrocidine and gramicidin S, and the topical antibiotic bacitracin. The ACV synthetase has three modules in a polypeptide of 450 kDa, while the heptapeptide scaffold of vancomycin or chloroeremomycin is assembled by three subunits with three, three, and one module, respectively. The enzymatic transformation of the acyclic ACV tripeptide to the bicyclic β-lactam structure of penicillins is catalyzed by a single nonheme FeII enzyme, isopenicillin N synthase (IPNS), that reduces cosubstrate O2 by four electrons to two molecules of water. In the chloroeremomycin cluster there are three hemeproteins, ORFs 7 to 9, and there are two homologs in the bahlimycin cluster that are implicated in genetic knockouts as the cross-linking catalysts. These putative cytochrome P450s could generate the phenolic radicals in the side chains of the heptapeptide substrates to initiate the cross-linkings. In most of the lipopeptide NRPS clusters sequenced to date, the acyltransferase responsible for N-acylation of the N-terminal amino acid does not map with the biosynthetic cluster and little is known about specificity. In the case of mycosubtilin, the first five domains of the MycA subunit are dedicated to construction of the C16-β-NH2-acyl group.
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Structural motifs in the catalytic and carrier domains of nonribosomal peptide synthetases.
Structural motifs in the catalytic and carrier domains of nonribosomal peptide synthetases.
Examples of antibiotics made on nonribosomal peptide synthetase assembly lines.
Examples of antibiotics made on nonribosomal peptide synthetase assembly lines.
NRPS assembly line organization: the three modules of ACV synthetase.
NRPS assembly line organization: the three modules of ACV synthetase.
Core domains of an NRPS elongation module: C-A-PCP and conversion of Apo PCP to Holo PCP domains by posttranslational phosphopantetheinylation.
Core domains of an NRPS elongation module: C-A-PCP and conversion of Apo PCP to Holo PCP domains by posttranslational phosphopantetheinylation.
Two steps of NRPS adenylation domain catalysis: selection and activation of amino acid as tightly bound aminoacyl-AMP; aminoacyl group transfer to generate the covalent aminoacyl-S-PCP intermediate.
Two steps of NRPS adenylation domain catalysis: selection and activation of amino acid as tightly bound aminoacyl-AMP; aminoacyl group transfer to generate the covalent aminoacyl-S-PCP intermediate.
Representative nonproteinogenic amino acids selected for chain incorporation by NRPS A domains.
Representative nonproteinogenic amino acids selected for chain incorporation by NRPS A domains.
C domain action in NRPS catalysis: peptide bond condensation and elongation via peptidyl chain transfer to the downstream PCP domain.
C domain action in NRPS catalysis: peptide bond condensation and elongation via peptidyl chain transfer to the downstream PCP domain.
(A) A-PCP two-domain chain initiation modules; (B) C-A-PCP-TE fourdomain chain termination modules and three different pathways of chain termination.
(A) A-PCP two-domain chain initiation modules; (B) C-A-PCP-TE fourdomain chain termination modules and three different pathways of chain termination.
Domain function in the ACV synthetase assembly Line: (A) action of the E domain to make D-Val-S-PCP3; (B) chain termination by the TE domain through deacylation of a tripeptidyl-O-Ser-TE acyl enzyme intermediate.
Domain function in the ACV synthetase assembly Line: (A) action of the E domain to make D-Val-S-PCP3; (B) chain termination by the TE domain through deacylation of a tripeptidyl-O-Ser-TE acyl enzyme intermediate.
Thirty genes clustered for chloroeremomycin biosynthesis.
Thirty genes clustered for chloroeremomycin biosynthesis.
A 24-domain, seven-module assembly line for the heptapeptide backbone of chloroeremomycin or vancomycin synthetase.
A 24-domain, seven-module assembly line for the heptapeptide backbone of chloroeremomycin or vancomycin synthetase.
The NRPS assembly line of tyrocidine synthetase.
The NRPS assembly line of tyrocidine synthetase.
Bacitracin chain release by intramolecular macrolactamization by the TE domain of bacitracin synthetase: making the Lys7-Asn12 isopeptide bond.
Bacitracin chain release by intramolecular macrolactamization by the TE domain of bacitracin synthetase: making the Lys7-Asn12 isopeptide bond.
Action of the cyclization domain of bacitracin synthetase to create the thiazoline ring from Cys1-Leu2.
Action of the cyclization domain of bacitracin synthetase to create the thiazoline ring from Cys1-Leu2.
Double cyclization of ACV to the β-lactam skeleton of penicillins by isopenicillin N synthase.
Double cyclization of ACV to the β-lactam skeleton of penicillins by isopenicillin N synthase.
Expansion of the five ring of penicillins to the six ring of cephalosporins by expandase (deacetoxycephalosporin C synthase).
Expansion of the five ring of penicillins to the six ring of cephalosporins by expandase (deacetoxycephalosporin C synthase).
X-ray structure of IPNS with active-site iron and bound ACV substrate.
X-ray structure of IPNS with active-site iron and bound ACV substrate.
Proposed mechanisms for the formation of the first ring (β-lactam) by IPNS.
Proposed mechanisms for the formation of the first ring (β-lactam) by IPNS.
Formation of the second ring of penicillins by IPNS with reduction of the ferryl intermediate.
Formation of the second ring of penicillins by IPNS with reduction of the ferryl intermediate.
Ring expansion by DAOCS with reduction of the ferryl intermediate.
Ring expansion by DAOCS with reduction of the ferryl intermediate.
The tandem action of CarA-C to generate the carbapenem nucleus.
The tandem action of CarA-C to generate the carbapenem nucleus.
Three oxidative transformations by CAS during construction of clavaminate.
Three oxidative transformations by CAS during construction of clavaminate.
Rigidifying cross-links connect the aryl side chains in the vancomycin family of antibiotics.
Rigidifying cross-links connect the aryl side chains in the vancomycin family of antibiotics.
Proposed phenoxy radical cyclization mechanisms for hemeprotein-mediated cross-linking in the vancomycin family.
Proposed phenoxy radical cyclization mechanisms for hemeprotein-mediated cross-linking in the vancomycin family.
Three regiospecific glycosyltransferases for tailoring of the aglycone in chloroeremomycin maturation.
Three regiospecific glycosyltransferases for tailoring of the aglycone in chloroeremomycin maturation.
Lipopeptides made by nonribosomal peptide synthetase assembly lines.
Lipopeptides made by nonribosomal peptide synthetase assembly lines.
N-Acylation machinery at the N terminus of the mycosubtilin synthetase assembly line.
N-Acylation machinery at the N terminus of the mycosubtilin synthetase assembly line.
NRP-PK hybrids: bleomycin, pristinamycin IIA, and rifampin, a member of the rifamycin family.
NRP-PK hybrids: bleomycin, pristinamycin IIA, and rifampin, a member of the rifamycin family.
NRP and PK modules in the (A) rifamycin and (B) bleomycin assembly lines.
NRP and PK modules in the (A) rifamycin and (B) bleomycin assembly lines.