title: Radical SAM enzyme QueE defines a new minimal core fold and metal-dependent mechanism.
abstract: 7-carboxy-7-deazaguanine synthase (QueE) catalyzes a key S-adenosyl-L-methionine (AdoMet)- and Mg(2+)-dependent radical-mediated ring contraction step, which is common to the biosynthetic pathways of all deazapurine-containing compounds. QueE is a member of the AdoMet radical superfamily, which employs the 5'-deoxyadenosyl radical from reductive cleavage of AdoMet to initiate chemistry. To provide a mechanistic rationale for this elaborate transformation, we present the crystal structure of a QueE along with structures of pre- and post-turnover states. We find that substrate binds perpendicular to the [4Fe-4S]-bound AdoMet, exposing its C6 hydrogen atom for abstraction and generating the binding site for Mg(2+), which coordinates directly to the substrate. The Burkholderia multivorans structure reported here varies from all other previously characterized members of the AdoMet radical superfamily in that it contains a hypermodified (β6/α3) protein core and an expanded cluster-binding motif, CX14CX2C.
authors.affiliation: 1] Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA. [2] Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Dowling
authors.affiliation: Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona, USA.
authors.forename: Nathan A
authors.initials: NA
authors.lastname: Bruender
authors.affiliation: Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona, USA.
authors.forename: Anthony P
authors.initials: AP
authors.lastname: Young
authors.affiliation: Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona, USA.
authors.forename: Reid M
authors.initials: RM
authors.lastname: McCarty
authors.affiliation: Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona, USA.
authors.forename: Vahe
authors.initials: V
authors.lastname: Bandarian
authors.affiliation: 1] Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA. [2] Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA. [3] Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA.
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Drennan
mesh_terms: D001665:Binding Sites; D019117:Burkholderia / Q000201:enzymology; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D006860:Hydrogen Bonding / Q000187:drug effects; D008274:Magnesium / Q000737:chemistry* / Q000494:pharmacology; D008345:Manganese / Q000737:chemistry* / Q000494:pharmacology; D008958:Models, Molecular; D015394:Molecular Structure; D017434:Protein Structure, Tertiary; D012436:S-Adenosylmethionine / Q000737:chemistry* / Q000378:metabolism*; D012964:Sodium / Q000737:chemistry* / Q000494:pharmacology
chemical_list: D005609:Free Radicals; D008345:Manganese; D012436:S-Adenosylmethionine; D012964:Sodium; D008274:Magnesium