@article {2020|2140, title = {Structural transitions in the RNA 7SK 5{\textquoteright} hairpin and their effect on HEXIM binding}, journal = {Nucleic Acids Res}, volume = {48}, year = {2020}, month = {01}, pages = {373-389}, abstract = {

7SK RNA, as part of the 7SK ribonucleoprotein complex, is crucial to the regulation of transcription by RNA-polymerase II, via its interaction with the positive transcription elongation factor P-TEFb. The interaction is induced by binding of the protein HEXIM to the 5\&$\#$39; hairpin (HP1) of 7SK RNA. Four distinct structural models have been obtained experimentally for HP1. Here, we employ computational methods to investigate the relative stability of these structures, transitions between them, and the effects of mutations on the observed structural ensembles. We further analyse the results with respect to mutational binding assays, and hypothesize a mechanism for HEXIM binding. Our results indicate that the dominant structure in the wild type exhibits a triplet involving the unpaired nucleotide U40 and the base pair A43-U66 in the GAUC/GAUC repeat. This conformation leads to an open major groove with enough potential binding sites for peptide recognition. Sequence mutations of the RNA change the relative stability of the different structural ensembles. Binding affinity is consequently lost if these changes alter the dominant structure.

}, doi = {10.1093/nar/gkz1071}, author = {R{\"o}der, Konstantin and Guillaume Stirnemann and Dock-Bregeon, Anne-Catherine and Wales, David J and Pasquali, Samuela} } @article {2018|2135, title = {Segmentation and the Entropic Elasticity of Modular Proteins}, journal = {J Phys Chem Lett}, volume = {9}, year = {2018}, month = {Aug}, pages = {4707-4713}, abstract = {

Single-molecule force spectroscopy utilizes polyproteins, which are composed of tandem modular domains, to study their mechanical and structural properties. Under the application of external load, the polyproteins respond by unfolding and refolding domains to acquire the most favored extensibility. However, unlike single-domain proteins, the sequential unfolding of the each domain modifies the free energy landscape (FEL) of the polyprotein nonlinearly. Here we use force-clamp (FC) spectroscopy to measure unfolding and collapse-refolding dynamics of polyubiquitin and poly(I91). Their reconstructed unfolding FEL involves hundreds of kB T in accumulating work performed against conformational entropy, which dwarfs the \∼30 kB T that is typically required to overcome the free energy difference of unfolding. We speculate that the additional entropic energy caused by segmentation of the polyprotein to individual proteins plays a crucial role in defining the \"shock absorber\" properties of elastic proteins such as the giant muscle protein titin.

}, doi = {10.1021/acs.jpclett.8b01925}, author = {Berkovich, Ronen and Fernandez, Vicente I and Guillaume Stirnemann and Valle-Orero, Jessica and Fernandez, Julio M} } @article {2016|1687, title = {Stability and Function at High Temperature. What Makes a Thermophilic GTPase Different from Its Mesophilic Homologue}, journal = {J. Phys. Chem. B}, volume = {120}, year = {2016}, pages = {2721{\textendash}2730}, abstract = {

Comparing homologous enzymes adapted to different thermal environments aids to shed light on their delicate stability/function trade-off. Protein mechanical rigidity was postulated to secure stability and high-temperature functionality of thermophilic proteins. In this work, we challenge the corresponding-state principle for a pair of homologous GTPase domains by performing extensive molecular dynamics simulations, applying conformational and kinetic clustering, as well as exploiting an enhanced sampling technique (REST2). While it was formerly shown that enhanced protein flexibility and high temperature stability can coexist in the apo hyperthermophilic variant, here we focus on the holo states of both homologues by mimicking the enzymatic turnover. We clearly show that the presence of the ligands affects the conformational landscape visited by the proteins, and that the corresponding state principle applies for some functional modes. Namely, in the hyperthermophilic species, the flexibility of the effec...

}, issn = {15205207}, doi = {10.1021/acs.jpcb.6b00306}, author = {Katava, Marina and Kalimeri, Maria and Guillaume Stirnemann and Fabio Sterpone} }