title: Structural and functional analysis of tetracenomycin F2 cyclase from Streptomyces glaucescens. A type II polyketide cyclase.
abstract: Tetracenomycin F2 cyclase (tcmI gene product), catalyzes an aromatic rearrangement in the biosynthetic pathway for tetracenomycin C in Streptomyces glaucescens. The x-ray structure of this small enzyme has been determined to 1.9-A resolution together with an analysis of site-directed mutants of potential catalytic residues. The protein exhibits a dimeric betaalphabeta ferredoxin-like fold that utilizes strand swapping between subunits in its assembly. The fold is dominated by four strands of antiparallel sheet and a layer of alpha-helices, which creates a cavity that is proposed to be the active site. This type of secondary structural arrangement has been previously observed in polyketide monooxygenases and suggests an evolutionary relationship between enzymes that catalyze adjacent steps in these biosynthetic pathways. Mutational analysis of all of the obvious catalytic bases within the active site suggests that the enzyme functions to steer the chemical outcome of the cyclization rather than providing a specific catalytic group. Together, the structure and functional analysis provide insight into the structural framework necessary to perform the complex rearrangements catalyzed by this class of polyketide cyclases.
authors.affiliation: Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Thompson
authors.forename: Kinya
authors.initials: K
authors.lastname: Katayama
authors.forename: Kenji
authors.initials: K
authors.lastname: Watanabe
authors.forename: C Richard
authors.initials: CR
authors.lastname: Hutchinson
authors.forename: Ivan
authors.initials: I
authors.lastname: Rayment
mesh_terms: D000446:Aldehyde-Lyases / Q000737:chemistry* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001483:Base Sequence; D002384:Catalysis; D018360:Crystallography, X-Ray; D017931:DNA Primers; D007700:Kinetics; D008958:Models, Molecular; D011487:Protein Conformation; D013302:Streptomyces / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; D000446:Aldehyde-Lyases; C083875:tetracenomycin F2 cyclase, Streptomyces