Studying biological assemblies with optical tweezers

by Ulrich Bockelmann (Laboratoire de Nanobiophysique, ESPCI, Paris)

Monday, February 18, 2013 from to (Europe/Berlin)
at AER 19 ( Room 3.11 )
Compared to an impressive body of knowledge that exists about the chemistry and the static structure of living cells and their components, the understanding of dynamic properties of biomolecules and of macromolecular aggregates is still in the beginning. This situation is changing thanks to techniques for investigation of functioning macromolecules at the single molecule level. In this talk we will first explain the manipulation of single molecules by optical tweezers and subsequently present two applications to the field of DNA, RNA and RNA-protein interactions.
In cells, DNA is constantly twisted, bended and stretched by numerous proteins mediating genome transactions. Understanding these essential biological processes requires in-depth knowledge of how DNA complies to mechanical stress. Double stranded DNA exhibits a structural transition at about 65 pN, where its contour length increases by ~70%. Using fluorescence microscopy in combination with optical tweezers, we unravelled the mechanisms behind this overstretching transition.
Ribosomal (r-) RNA is well structured in the ribosome, but the role of r-proteins in the assembly process is poorly understood. We address this question by using optical tweezers to unfold RNA fragments in the presence or absence of proteins. We studied the case of Escherichia coli L20, an early binding r-protein that recognizes an essential subdomain of the 23S rRNA. We found that L20 acts as a clamp that makes RNA fragments surrounding its binding sites more resistant to mechanical unfolding.