Multistage Collapse of a Bacterial Ribozyme Observed by Time-Resolved Small-Angle X-ray Scattering

Journal Article · Tue Aug 03 04:00:00 EDT 2010 · J. Am. Chem. Soc.

DOI:https://doi.org/10.1021/ja103867p· OSTI ID:1002552

Roh, Joon Ho; Guo, Liang; Kilburn, J Duncan; Briber, Robert M; Irving, Thomas; Woodson, Sarah A ^[1]

---

1. IIT

Ribozymes must fold into compact, native structures to function properly in the cell. The first step in forming the RNA tertiary structure is the neutralization of the phosphate charge by cations, followed by collapse of the unfolded molecules into more compact structures. The specificity of the collapse transition determines the structures of the folding intermediates and the folding time to the native state. However, the forces that enable specific collapse in RNA are not understood. Using time-resolved SAXS, we report that upon addition of 5 mM Mg{sup 2+} to the Azoarcus group I ribozyme up to 80% of chains form compact structures in less than 1 ms. In 1 mM Mg{sup 2+}, the collapse transition produces extended structures that slowly approach the folded state, while {ge} 1.5 mM Mg{sup 2+} leads to an ensemble of random coils that fold with multistage kinetics. Increased flexibility of molecules in the intermediate ensemble correlates with a Mg{sup 2+}-dependent increase in the fast folding population and a previously unobserved crossover in the collapse kinetics. Partial denaturation of the unfolded RNA with urea also increases the fraction of chains following the fast-folding pathway. These results demonstrate that the preferred collapse mechanism depends on the extent of Mg{sup 2+}-dependent charge neutralization and that non-native interactions within the unfolded ensemble contribute to the heterogeneity of the ribozyme folding pathways at the very earliest stages of tertiary structure formation.

• Research Organization: Advanced Photon Source (APS), Argonne National Laboratory (ANL), Argonne, IL (US)
• Sponsoring Organization: USDOE
• OSTI ID: 1002552
• Journal Information: J. Am. Chem. Soc., Journal Name: J. Am. Chem. Soc. Journal Issue: (29) ; 07, 2010 Vol. 132; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: ENGLISH

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
99 GENERAL AND MISCELLANEOUS
CATIONS
CHAINS
FLEXIBILITY
KINETICS
PHOSPHATES
RNA
SCATTERING
SPECIFICITY
UREA