pH jump studies of the folding of the multidomain ribosomal protein L9: the structural organization of the N-terminal domain does not affect the anomalously slow folding of the C-terminal domain.
The folding kinetics of the multidomain ribosomal protein L9 were studied using pH jump stopped-flow fluorescence and circular dichroism (CD) in conjunction with guanidine hydrochloride (GdnHCl) jump stopped-flow CD experiments. Equilibrium CD and 1D (1)H NMR measurements demonstrated that the C-terminal domain unfolds below pH 4 while the N-terminal domain remains fully folded. Thus, the N-terminal domain remains folded during the pH jump experiments. The folding rate constant of the C-terminal domain was determined to be 3.5 s(-1) by pH jump experiments conducted in the absence of denaturant using stopped-flow CD and fluorescence. CD-detected GdnHCl jump measurements showed that the N- and C-terminal domains fold independently each by an apparent two-state mechanism. The folding rate constant for the N-terminal domain and the C-terminal domain in the absence of denaturant were calculated to be 760 and 4. 7 s(-1), respectively. The good agreement between the pH jump and the denaturant concentration jump experiments shows that the folding rate of the C-terminal domain is the same whether or not the N-terminal domain is folded. This result suggests that the slow folding of the C-terminal domain is not a consequence of unfavorable interactions with the rest of the protein chain during refolding. This is an interesting result since contact order analysis predicts that the folding rate of the C-terminal domain should be noticeably faster. The folding rate of the isolated N-terminal domain was also measured by stopped-flow CD and was found to be the same as the rate for the domain in the intact protein.
Sato
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S
Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, USA.
Luisi
D L
DL
Raleigh
D P
DP
D000143:Acids / Q000494:pharmacology; D002942:Circular Dichroism; D017666:Deuterium Oxide / Q000378:metabolism; D005453:Fluorescence; D001411:Geobacillus stearothermophilus / Q000737:chemistry*; D019791:Guanidine / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011489:Protein Denaturation / Q000187:drug effects; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012269:Ribosomal Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion / Q000235:genetics; D013816:Thermodynamics
D000143:Acids; D010446:Peptide Fragments; D012269:Ribosomal Proteins; C049650:ribosomal protein L9; D017666:Deuterium Oxide; D019791:Guanidine