Variable helix elongation as a tool to modulate RNA alignment and motional couplings.

Published

Journal Article

The application of residual dipolar couplings (RDCs) in studies of RNA structure and dynamics can be complicated by the presence of couplings between collective helix motions and overall alignment and by the inability to modulate overall alignment of the molecule by changing the ordering medium. Here, we show for a 27-nt TAR RNA construct that variable levels of helix elongation can be used to alter both overall alignment and couplings to collective helix motions in a semi-predictable manner. In the absence of elongation, a four base-pair helix II capped by a UUCG apical loop exhibits a higher degree of order compared to a six base-pair helix I (theta(I)/theta(II)=0.56+/-0.1). The principal S(zz) direction is nearly parallel to the axis of helix II but deviates by approximately 40 degrees relative to the axis of helix I. Elongating helix I by three base-pairs equalizes the alignment of the two helices and pushes the RNA into the motional coupling limit such that the two helices have comparable degrees of order (theta(I)/theta(II)=0.92+/-0.04) and orientations relative to S(zz) ( approximately 17 degrees ). Increasing the length of elongation further to 22 base-pairs pushes the RNA into the motional decoupling limit in which helix I dominates alignment (theta(II)/theta(I)=0.45+/-0.05), with S(zz) orientated nearly parallel to its helix axis. Many of these trends can be rationalized using PALES simulations that employ a previously proposed three-state dynamic ensemble of TAR. Our results provide new insights into motional couplings, offer guidelines for assessing their extent, and suggest that variable degrees of helix elongation can allow access to independent sets of RDCs for characterizing RNA structural dynamics.

Full Text

Duke Authors

Cited Authors

  • Dethoff, EA; Hansen, AL; Zhang, Q; Al-Hashimi, HM

Published Date

  • January 2010

Published In

Volume / Issue

  • 202 / 1

Start / End Page

  • 117 - 121

PubMed ID

  • 19854083

Pubmed Central ID

  • 19854083

Electronic International Standard Serial Number (EISSN)

  • 1096-0856

International Standard Serial Number (ISSN)

  • 1090-7807

Digital Object Identifier (DOI)

  • 10.1016/j.jmr.2009.09.022

Language

  • eng