title: Substrate-Induced Allosteric Change in the Quaternary Structure of the Spermidine N-Acetyltransferase SpeG.
abstract: The spermidine N-acetyltransferase SpeG is a dodecameric enzyme that catalyzes the transfer of an acetyl group from acetyl coenzyme A to polyamines such as spermidine and spermine. SpeG has an allosteric polyamine-binding site and acetylating polyamines regulate their intracellular concentrations. The structures of SpeG from Vibrio cholerae in complexes with polyamines and cofactor have been characterized earlier. Here, we present the dodecameric structure of SpeG from V. cholerae in a ligand-free form in three different conformational states: open, intermediate and closed. All structures were crystallized in C2 space group symmetry and contain six monomers in the asymmetric unit cell. Two hexamers related by crystallographic 2-fold symmetry form the SpeG dodecamer. The open and intermediate states have a unique open dodecameric ring. This SpeG dodecamer is asymmetric except for the one 2-fold axis and is unlike any known dodecameric structure. Using a fluorescence thermal shift assay, size-exclusion chromatography with multi-angle light scattering, small-angle X-ray scattering analysis, negative-stain electron microscopy and structural analysis, we demonstrate that this unique open dodecameric state exists in solution. Our combined results indicate that polyamines trigger conformational changes and induce the symmetric closed dodecameric state of the protein when they bind to their allosteric sites.
authors.affiliation: Center for Structural Genomics of Infectious Diseases, Feinberg School of Medicine, Department of Biochemistry and Molecular Genetics, Northwestern University , Chicago, IL 60611, USA.
authors.forename: Ekaterina V
authors.initials: EV
authors.lastname: Filippova
authors.affiliation: DuPont-Northwestern-Dow Collaborative Access Team, Northwestern University Synchrotron Research Center, Argonne, IL 60439, USA.
authors.forename: Steven
authors.initials: S
authors.lastname: Weigand
authors.affiliation: Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: Jerzy
authors.initials: J
authors.lastname: Osipiuk
authors.affiliation: Center for Structural Genomics of Infectious Diseases, Feinberg School of Medicine, Department of Biochemistry and Molecular Genetics, Northwestern University , Chicago, IL 60611, USA.
authors.forename: Olga
authors.initials: O
authors.lastname: Kiryukhina
authors.affiliation: Biosciences Division, Argonne National Laboratory, Argonne, IL 60439, USA.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Joachimiak
authors.affiliation: Center for Structural Genomics of Infectious Diseases, Feinberg School of Medicine, Department of Biochemistry and Molecular Genetics, Northwestern University , Chicago, IL 60611, USA. Electronic address: wf-anderson@northwestern.edu.
authors.forename: Wayne F
authors.initials: WF
authors.lastname: Anderson
mesh_terms: D000105:Acetyl Coenzyme A / Q000378:metabolism*; D000107:Acetylation; D000123:Acetyltransferases / Q000737:chemistry* / Q000378:metabolism*; D000495:Allosteric Site; D000595:Amino Acid Sequence; D002384:Catalysis; D018360:Crystallography, X-Ray; D007700:Kinetics; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D011073:Polyamines / Q000378:metabolism*; D011487:Protein Conformation; D053838:Scattering, Small Angle; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014734:Vibrio cholerae / Q000378:metabolism; D000099228:Diamine N-Acetyltransferase
chemical_list: D000105:Acetyl Coenzyme A; D000123:Acetyltransferases; D011073:Polyamines; D000099228:Diamine N-Acetyltransferase
keywords: GNAT acetyltransferase; allosteric site; asymmetric structure; dodecameric enzyme; spermidine/spermine