Tags

Type your tag names separated by a space and hit enter

Ketosynthases in the initiation and elongation modules of aromatic polyketide synthases have orthogonal acyl carrier protein specificity.
Biochemistry. 2003 Jun 03; 42(21):6588-95.B

Abstract

Many bacterial aromatic polyketides are synthesized by type II polyketide synthases (PKSs) which minimally consist of a ketosynthase-chain length factor (KS-CLF) heterodimer, an acyl carrier protein (ACP), and a malonyl-CoA:ACP transacylase (MAT). This minimal PKS initiates polyketide biosynthesis by decarboxylation of malonyl-ACP, which is catalyzed by the KS-CLF complex and leads to incorporation of an acetate starter unit. In non-acetate-primed PKSs, such as the frenolicin (fren) PKS and the R1128 PKS, decarboxylative priming is suppressed in favor of chain initiation with alternative acyl groups. Elucidation of these unusual priming pathways could lead to the engineered biosynthesis of polyketides containing novel starter units. Unique to some non-acetate-primed PKSs is a second catalytic module comprised of a dedicated homodimeric KS, an additional ACP, and a MAT. This initiation module is responsible for starter-unit selection and catalysis of the first chain elongation step. To elucidate the protein-protein recognition features of this dissociated multimodular PKS system, we expressed and purified two priming and two elongation KSs, a set of six ACPs from diverse sources, and a MAT. In the presence of the MAT, each ACP was labeled with malonyl-CoA rapidly. In the presence of a KS-CLF and MAT, all ACPs from minimal PKSs supported polyketide synthesis at comparable rates (k(cat) between 0.17 and 0.37 min(-1)), whereas PKS activity was attenuated by at least 50-fold in the presence of an ACP from an initiation module. In contrast, the opposite specificity pattern was observed with priming KSs: while ACPs from initiation modules were good substrates, ACPs from minimal PKSs were significantly poorer substrates. Our results show that KS-CLF and KSIII recognize orthogonal sets of ACPs, and the additional ACP is indispensable for the incorporation of non-acetate primer units. Sequence alignments of the two classes of ACPs identified a tyrosine residue that is unique to priming ACPs. Site-directed mutagenesis of this amino acid in the initiation and elongation module ACPs of the R1128 PKS confirmed the importance of this residue in modulating interactions between KSs and ACPs. Our study provides new biochemical insights into unusual chain initiation mechanisms of bacterial aromatic PKSs.

Authors+Show Affiliations

Department of Chemical Engineering, Stanford University, Stanford, California 94305-5025, USA.No affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, U.S. Gov't, P.H.S.

Language

eng

PubMed ID

12767243

Citation

Tang, Yi, et al. "Ketosynthases in the Initiation and Elongation Modules of Aromatic Polyketide Synthases Have Orthogonal Acyl Carrier Protein Specificity." Biochemistry, vol. 42, no. 21, 2003, pp. 6588-95.
Tang Y, Lee TS, Kobayashi S, et al. Ketosynthases in the initiation and elongation modules of aromatic polyketide synthases have orthogonal acyl carrier protein specificity. Biochemistry. 2003;42(21):6588-95.
Tang, Y., Lee, T. S., Kobayashi, S., & Khosla, C. (2003). Ketosynthases in the initiation and elongation modules of aromatic polyketide synthases have orthogonal acyl carrier protein specificity. Biochemistry, 42(21), 6588-95.
Tang Y, et al. Ketosynthases in the Initiation and Elongation Modules of Aromatic Polyketide Synthases Have Orthogonal Acyl Carrier Protein Specificity. Biochemistry. 2003 Jun 3;42(21):6588-95. PubMed PMID: 12767243.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Ketosynthases in the initiation and elongation modules of aromatic polyketide synthases have orthogonal acyl carrier protein specificity. AU - Tang,Yi, AU - Lee,Taek Soon, AU - Kobayashi,Seiji, AU - Khosla,Chaitan, PY - 2003/5/28/pubmed PY - 2003/7/17/medline PY - 2003/5/28/entrez SP - 6588 EP - 95 JF - Biochemistry JO - Biochemistry VL - 42 IS - 21 N2 - Many bacterial aromatic polyketides are synthesized by type II polyketide synthases (PKSs) which minimally consist of a ketosynthase-chain length factor (KS-CLF) heterodimer, an acyl carrier protein (ACP), and a malonyl-CoA:ACP transacylase (MAT). This minimal PKS initiates polyketide biosynthesis by decarboxylation of malonyl-ACP, which is catalyzed by the KS-CLF complex and leads to incorporation of an acetate starter unit. In non-acetate-primed PKSs, such as the frenolicin (fren) PKS and the R1128 PKS, decarboxylative priming is suppressed in favor of chain initiation with alternative acyl groups. Elucidation of these unusual priming pathways could lead to the engineered biosynthesis of polyketides containing novel starter units. Unique to some non-acetate-primed PKSs is a second catalytic module comprised of a dedicated homodimeric KS, an additional ACP, and a MAT. This initiation module is responsible for starter-unit selection and catalysis of the first chain elongation step. To elucidate the protein-protein recognition features of this dissociated multimodular PKS system, we expressed and purified two priming and two elongation KSs, a set of six ACPs from diverse sources, and a MAT. In the presence of the MAT, each ACP was labeled with malonyl-CoA rapidly. In the presence of a KS-CLF and MAT, all ACPs from minimal PKSs supported polyketide synthesis at comparable rates (k(cat) between 0.17 and 0.37 min(-1)), whereas PKS activity was attenuated by at least 50-fold in the presence of an ACP from an initiation module. In contrast, the opposite specificity pattern was observed with priming KSs: while ACPs from initiation modules were good substrates, ACPs from minimal PKSs were significantly poorer substrates. Our results show that KS-CLF and KSIII recognize orthogonal sets of ACPs, and the additional ACP is indispensable for the incorporation of non-acetate primer units. Sequence alignments of the two classes of ACPs identified a tyrosine residue that is unique to priming ACPs. Site-directed mutagenesis of this amino acid in the initiation and elongation module ACPs of the R1128 PKS confirmed the importance of this residue in modulating interactions between KSs and ACPs. Our study provides new biochemical insights into unusual chain initiation mechanisms of bacterial aromatic PKSs. SN - 0006-2960 UR - https://www.unboundmedicine.com/medline/citation/12767243/Ketosynthases_in_the_initiation_and_elongation_modules_of_aromatic_polyketide_synthases_have_orthogonal_acyl_carrier_protein_specificity_ L2 - https://dx.doi.org/10.1021/bi0341962 DB - PRIME DP - Unbound Medicine ER -