pH-dependent and ligand induced conformational changes of eucaryotic protein synthesis initiation factor eIF-(iso)4F: a circular dichroism study.
The structural features of wheat germ protein synthesis initiation factor eIF-(iso)4F, which has a cap binding protein as one of its two subunits, are unknown. In this study, circular dichroism (CD) spectra and secondary structure prediction were obtained for eIF-(iso)4F and its two subunits, p28 and p86. The alpha-helix content of eIF-(iso)4F changed from 42% at pH 6.3 to 15% at pH 7.6, the optimum pH for cap binding. The beta-sheet content increased from 14% (pH 6.3) to 38% at pH 7.6. The CD spectra of the two subunits, p28 and p86 were also measured and analyzed. The separated subunits both had a higher alpha-helix content at pH 7.6 than the native protein, giving values of 60% and 34% alpha-helix for p28 and p86, respectively. Binding of the dinucleotide cap analog to p28 reduced the alpha-helix content to approximately 8% with an increase in the beta sheet content from 10% to 37%. The conformational changes in eIF-(iso)4F upon binding with mRNA are dependent on cap or oligonucleotide structure. A conformation consisting of approximately the same alpha-helix and beta-sheet content can be induced by ligands even at non-optimal pH values. This large conformational transition suggests eIF-(iso)4F binds nucleic acids by interaction of a beta-sheet motif and that this conformational transition may have a regulatory role.
Wang
Y
Y
Department of Chemistry, Hunter College, City University of New York, NY 10021, USA.
Sha
M
M
Ren
W Y
WY
van Heerden
A
A
Browning
K S
KS
Goss
D J
DJ
D002942:Circular Dichroism; D015977:Eukaryotic Initiation Factor-1 / Q000737:chemistry* / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D009690:Nucleic Acid Conformation; D010448:Peptide Initiation Factors / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D039381:RNA Cap-Binding Proteins; D016601:RNA-Binding Proteins / Q000737:chemistry; D014908:Triticum / Q000737:chemistry*
D015977:Eukaryotic Initiation Factor-1; D008024:Ligands; D010448:Peptide Initiation Factors; D039381:RNA Cap-Binding Proteins; D016601:RNA-Binding Proteins; C075833:eIF-4