Site-specific observation of acyl intermediate processing in thiotemplate biosynthesis by fourier transform mass spectrometry: the polyketide module of yersiniabactin synthetase.
Complex arrays of thioester bound intermediates are present on 100-700 kDa enzymes during the biogenesis of diverse types of pharmacophores and natural product drugs. These multidomain enzymes, known as nonribosomal peptide synthetases and polyketide synthases (NRPSs and PKSs, respectively), synthesize from simple, physiologically available substrates bioactive compounds that can be further tailored by a host of modifying domains (e.g., methylation, cyclization, and epimerization) to increase the complexity of the mature final product. Interrogation of such covalent intermediates using mass spectrometry (MS) presents an underutilized method for understanding the covalent catalysis executed by NRPS and PKS enzymes. For the PKS module (205 kDa) from the yersiniabactin (Ybt) gene cluster of Yersinia pestis, limited proteolysis afforded a key 11 kDa peptide from the acyl-carrier protein (ACP) domain upon which at least five covalent intermediates could be detected (42, 70, 86, 330, and 358 Da). The isotopic resolution achieved by Fourier transform mass spectrometry (FTMS) allowed for the incorporation of substrates with stable isotopes to confirm the structural assignments of three intermediates (86, 330, and 358 Da) on the Ybt biosynthetic pathway to within 1 Da. Approximately 75% of the enzyme capacity is lost to unproductive decarboxylation of malonyl-S-ACP partly constraining the 1.4 min(-)(1) rate of Ybt production in vitro. Acyl transfer to the ACP domain (on the Ybt pathway) was promoted by a factor of approximately 10 over unproductive CO(2) loss in the presence of the cosubstrate S-adenosylmethionine (SAM), with S-adenosylhomocysteine unable to restore the condensation yield observed with SAM. The data are consistent with Claisen condensation from KS to the ACP carrier site being reversible, with the absence of downstream methylation providing more opportunity for unproductive CO(2) loss. Extension of such FTMS-based studies will allow the direct visualization of multiple intermediates in determining the catalytic order of events and kinetics of NRPS and PKS systems.
Mazur
Matthew T
MT
Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Walsh
Christopher T
CT
Kelleher
Neil L
NL
D000213:Acyl Carrier Protein / Q000737:chemistry / Q000378:metabolism*; D000215:Acylation; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D003653:Decarboxylation; D004952:Esters / Q000737:chemistry / Q000378:metabolism*; D005583:Fourier Analysis; D033862:Iron-Binding Proteins; D007700:Kinetics; D008316:Malonyl Coenzyme A / Q000378:metabolism; D013058:Mass Spectrometry / Q000379:methods; D009097:Multienzyme Complexes / Q000096:biosynthesis* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010453:Peptide Synthases / Q000737:chemistry / Q000378:metabolism*; D033902:Periplasmic Binding Proteins; D010636:Phenols; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism; D017262:Siderophores / Q000096:biosynthesis* / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000737:chemistry / Q000378:metabolism; D013844:Thiazoles; D015010:Yersinia pestis / Q000201:enzymology / Q000235:genetics
D000213:Acyl Carrier Protein; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004952:Esters; D033862:Iron-Binding Proteins; D009097:Multienzyme Complexes; D033902:Periplasmic Binding Proteins; D010636:Phenols; D011994:Recombinant Proteins; D017262:Siderophores; D013438:Sulfhydryl Compounds; D013844:Thiazoles; C104398:yersiniabactin; D008316:Malonyl Coenzyme A; D012436:S-Adenosylmethionine; D010453:Peptide Synthases; C104385:non-ribosomal peptide synthase