title: The N-terminal domain (IF2N) of bacterial translation initiation factor IF2 is connected to the conserved C-terminal domains by a flexible linker.
abstract: Bacterial translation initiation factor IF2 is a multidomain protein that is an essential component of a system for ensuring that protein synthesis begins at the correct codon within a messenger RNA. Full-length IF2 from Escherichia coli and seven fragments of the protein were expressed, purified, and characterized using nuclear magnetic resonance (NMR) and circular dichroism (CD) methods. Interestingly, resonances of the 6 kD IF2N domain located at the extreme N terminus of IF2 can be clearly identified within the NMR spectra of the full-length 97-kD protein. (15)N NMR relaxation rate data indicate that (1) the IF2N domain is internally well ordered and tumbles in solution in a manner that is independent of the other domains of the IF2 protein, and (2) the IF2N domain is connected to the C-terminal regions of IF2 by a flexible linker. Chemical shifts of resonances within the isolated IF2N domain do not significantly differ from those of the corresponding residues within the context of the full-length 97-kD protein, indicating that IF2N is a structurally independent unit that does not strongly interact with other regions of IF2. CD and NMR data together provide evidence that Domains I-III of IF2 have unstructured and flexible regions as well as substantial helical content; CD data indicate that the helical content of these regions decreases significantly at temperatures above 35 degrees C. The features of structurally well-ordered N- and C-terminal domains connected by a flexible linker with significant helical content are reminiscent of another translation initiation factor, IF3.
authors.affiliation: Department of Molecular Biology, University of Aarhus, Aarhus, Denmark.
authors.forename: Brian Søgaard
authors.initials: BS
authors.lastname: Laursen
authors.forename: Anne Cecillie
authors.initials: AC
authors.lastname: Kjaergaard
authors.forename: Kim Kusk
authors.initials: KK
authors.lastname: Mortensen
authors.forename: David W
authors.initials: DW
authors.lastname: Hoffman
authors.forename: Hans Uffe
authors.initials: HU
authors.lastname: Sperling-Petersen
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D003001:Cloning, Molecular; D003198:Computer Simulation; D017124:Conserved Sequence; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D019906:Nuclear Magnetic Resonance, Biomolecular; D010446:Peptide Fragments / Q000032:analysis / Q000737:chemistry; D039881:Prokaryotic Initiation Factor-2 / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012996:Solutions / Q000737:chemistry; D013696:Temperature
chemical_list: D029968:Escherichia coli Proteins; D010446:Peptide Fragments; D039881:Prokaryotic Initiation Factor-2; D012996:Solutions