Differential effects of ribosomal proteins and Mg2+ ions on a conformational switch during 30S ribosome 5'-domain assembly.
Ribosomal protein S4 nucleates assembly of the 30S ribosome 5' and central domains, which is crucial for the survival of cells. Protein S4 changes the structure of its 16S rRNA binding site, passing through a non-native intermediate complex before forming native S4-rRNA contacts. Ensemble FRET was used to measure the thermodynamic stability of non-native and native S4 complexes in the presence of Mg(2+) ions and other 5'-domain proteins. Equilibrium titrations of Cy3-labeled 5'-domain RNA with Cy5-labeled protein S4 showed that Mg(2+) ions preferentially stabilize the native S4-rRNA complex. In contrast, ribosomal proteins S20 and S16 act by destabilizing the non-native S4-rRNA complex. The full cooperative switch to the native complex requires S4, S16, and S20 and is achieved to a lesser degree by S4 and S16. The resulting thermodynamic model for assembly of the 30S body illustrates how ribosomal proteins selectively bias the equilibrium between alternative rRNA conformations, increasing the cooperativity of rRNA folding beyond what can be achieved by Mg(2+) ions alone.
T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Sanjaya C
SC
Abeysirigunawardena
T.C. Jenkins Department of Biophysics, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Sarah A
SA
Woodson
D001665:Binding Sites / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D011485:Protein Binding / Q000235:genetics; D011487:Protein Conformation; D017434:Protein Structure, Tertiary / Q000235:genetics*; D012335:RNA, Ribosomal / Q000235:genetics* / Q000378:metabolism; D012269:Ribosomal Proteins / Q000235:genetics / Q000378:metabolism*; D012270:Ribosomes / Q000235:genetics* / Q000378:metabolism; D013816:Thermodynamics
D012335:RNA, Ribosomal; D012269:Ribosomal Proteins; D008274:Magnesium
FRET; RNA–protein interactions; ribosomal protein S4; ribosome assembly