Complex enzymes perform multi-step catalysis in biosynthetic pathways in which labile or insoluble intermediates are channeled or transported between active sites. We propose to continue our structural studies of one complex enzyme system, the glutamine amidotransferases, and to initiate work on a second, the curacin polyketide synthase. The glutamine amidotransferases are biosynthetic enzymes that generate ammonia from glutamine in one active site and channel it to a second active site for addition to a second substrate.
In Aim 1, we will continue studies of GatCAB, which catalyzes the second half of tRNAGln or tRNAAsn aminoacylation in organisms lacking a glutamine tRNA synthetase or asparagine tRNA synthetase. Specifically, we will examine complexes of Aquifex aeolicus GatCAB with tRNA and substrate-like small molecules. These studies aim to understand how the GatB subunit recognizes mis-charged Glu-tRNAGln or Asp-tRNAAsn, how tRNA binding stimulates ammonia production in the GatA subunit, how ammonia is channeled between subunits, and what is the structure-based mechanism of nucleophilic addition of nitrogen in GatB to produce Gln-tRNAGln or Asn-tRNAAsn.
In Aims 2 and 3, we will focus on a new class of complex enzymes, the modular polyketide synthases (PKSs). Microbes produce an astounding variety of polyketide natural products, which are an important source of new bio-active molecules that can be exploited as lead compounds for development of new pharmaceuticals. In these mega-enzymes, a carrier domain transports insoluble intermediates between enzyme active sites. Our subject is the PKS for curacin A, a polyketide with anti-tubulin activity. We will study the structural biochemistry of three unusual chemical features of curacin: a cyclopropane ring, a cis double bond, and a terminal alkene. We will produce relevant catalytic domains encoded by the 75-kilobase curacin gene cluster, determine crystal structures of the domains and of their substrate or analog complexes, and examine catalytic specificity. The result of these studies will be an understanding of how the curacin PKS carries out its unusual chemical transformations, and to what extent the catalytic domains can tolerate substrate variants.

Public Health Relevance

Many enzymes perform complex multi-step chemical reactions. This project will examine the details of substrate interactions with several complex enzymes by solving crystal structures of enzyme-substrate or -analog complexes. The goal is to understand how catalytic domains of proteins channel a reaction product to the site of the next reaction. ? ? ? ?

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
Project #
Application #
Study Section
Macromolecular Structure and Function E Study Section (MSFE)
Program Officer
Sechi, Salvatore
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
University of Michigan Ann Arbor
Schools of Medicine
Ann Arbor
United States
Zip Code
Skiba, Meredith A; Sikkema, Andrew P; Moss, Nathan A et al. (2018) Biosynthesis of t-Butyl in Apratoxin A: Functional Analysis and Architecture of a PKS Loading Module. ACS Chem Biol 13:1640-1650
Dodge, Greg J; Maloney, Finn P; Smith, Janet L (2018) Protein-protein interactions in ""cis-AT"" polyketide synthases. Nat Prod Rep 35:1082-1096
Dodge, Greg J; Ronnow, Danialle; Taylor, Richard E et al. (2018) Molecular Basis for Olefin Rearrangement in the Gephyronic Acid Polyketide Synthase. ACS Chem Biol 13:2699-2707
Skiba, Meredith A; Bivins, Marissa M; Schultz, John R et al. (2018) Structural Basis of Polyketide Synthase O-Methylation. ACS Chem Biol :
Skiba, Meredith A; Maloney, Finn P; Dan, Qingyun et al. (2018) PKS-NRPS Enzymology and Structural Biology: Considerations in Protein Production. Methods Enzymol 604:45-88
Tripathi, Ashootosh; Park, Sung Ryeol; Sikkema, Andrew P et al. (2018) A Defined and Flexible Pocket Explains Aryl Substrate Promiscuity of the Cahuitamycin Starter Unit-Activating Enzyme CahJ. Chembiochem 19:1595-1600
Skiba, Meredith A; Sikkema, Andrew P; Moss, Nathan A et al. (2017) A Mononuclear Iron-Dependent Methyltransferase Catalyzes Initial Steps in Assembly of the Apratoxin A Polyketide Starter Unit. ACS Chem Biol 12:3039-3048
Maloney, Finn P; Gerwick, Lena; Gerwick, William H et al. (2016) Anatomy of the ?-branching enzyme of polyketide biosynthesis and its interaction with an acyl-ACP substrate. Proc Natl Acad Sci U S A 113:10316-21
Stull, Frederick W; Bernard, Steffen M; Sapra, Aparna et al. (2016) Deprotonations in the Reaction of Flavin-Dependent Thymidylate Synthase. Biochemistry 55:3261-9
Skiba, Meredith A; Sikkema, Andrew P; Fiers, William D et al. (2016) Domain Organization and Active Site Architecture of a Polyketide Synthase C-methyltransferase. ACS Chem Biol 11:3319-3327

Showing the most recent 10 out of 71 publications