title: Oligomeric assemblies of the Escherichia coli MalT transcriptional activator revealed by cryo-electron microscopy and image processing.
abstract: MalT, the dedicated transcriptional activator of the maltose regulon in Escherichia coli, is the prototype for a family of large (approximately 100 kDa) transcriptional activators. MalT self-association plays a key role in recognition of the target promoters, which contain several MalT sites that are cooperatively bound by the activator. The unliganded form of MalT is monomeric. The protein self-associates only in the presence of both ATP (or AMP-PNP, a non-hydrolysable analog of ATP) and maltotriose, the inducer. Here, we report cryo-electron microscopy analyses of MalT multimeric forms. We show that, in the presence of maltotriose and AMP-PNP, MalT associates into novel, polydisperse, curved homopolymers. The building block, corresponding to a MalT monomer, comprises an outer globular domain connected by a peduncle to an inner domain that mediates self-association. Image analyses highlight the significant conformational flexibility of these polymeric forms. In the presence of a DNA fragment containing a MalT-controlled promoter, malPp500, MalT forms homopolymers with a much smaller radius of curvature and a different conformation. We propose that MalT binding to the target promoters involves the assembly of a MalT homo-oligomer that is governed by the array of MalT sites present.
authors.affiliation: Groupe de Microscopie Structurale Moléculaire, CNRS URA 2185, Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris Cedex 15, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Larquet
authors.forename: Valérie
authors.initials: V
authors.lastname: Schreiber
authors.forename: Nicolas
authors.initials: N
authors.lastname: Boisset
authors.forename: Evelyne
authors.initials: E
authors.lastname: Richet
mesh_terms: D020285:Cryoelectron Microscopy; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D004926:Escherichia coli / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D015999:Multivariate Analysis; D009698:Nucleoproteins / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D011401:Promoter Regions, Genetic; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; C058976:MalT protein, E coli; D009698:Nucleoproteins; D014157:Transcription Factors