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Telomerase is a specialized reverse transcriptase that is responsible for telomere length maintenance. As in other organisms, the minimal components required for an active human telomerase are the template-providing telomerase RNA (hTR) and the enzymatic entity telomerase reverse transcriptase (hTERT). Here, we explored the structure of hTR and the hTERT-induced conformational changes within hTR in living cells. By employing an in vivo DMS chemical probing technique, we showed that the pseudoknot and associated triple helical scaffold form stably in vivo independently of hTERT. In fact, the dimethyl-sulfate (DMS) modification pattern suggests that hTR alone is capable of adopting a conformation that is suited to interact with hTERT. However, in the absence of hTERT the template region of hTR is only weakly accessible to DMS-modifications. The predominant change after binding of hTERT to hTR is the exposure of the template region.

The 37 kDa/67 kDa laminin receptor (LRP/LR) represents a key player for cell adhesion, is associated with the metastatic potential of solid tumors and is required for maintenance of cell viability by preventing apoptosis. LRP/LR acts as a receptor for viruses such as Sindbis virus, Venezuelean Equine Encephalitis (VEE) virus, Adeno-associated-viruses (AAV) and Dengue Virus, the latter causing 50 to 100 million infections in humans per year. LRP/LR acts further as a receptor for prions and represents a multifunctional protein subcellularly located to the nucleus, the cytoplasm and the cell surface. The receptor represents an alternative target for therapy of viral infections, cancer and prion disorders and might play additional roles in further neurodegenerative diseases such as Alzheimer's disease. The species barrier in prion disorders might be at least in part determined by the presence of LRP/LR in enterocytes of the intestinal epithelium. Anti-LRP/LR antibodies, siRNAs directed against LRP mRNA, polysulfated glycanes such as pentosan polysulfate and heparan mimetics and LRP decoy mutants are promising tools for blocking or downregulating the receptor and may represent alternative therapeutics for the treatment of prion disorders, Alzheimer's Disease and metastatic cancer.

Mutations in the telomerase complex disrupt either nucleic acid binding or catalysis, and are the cause of numerous human diseases. Despite its importance, the structure of the human telomerase complex has not been observed crystallographically, nor are its dynamics understood in detail. Fragments of this complex from Tetrahymena thermophila and Tribolium castaneum have been crystallized. Biochemical probes provide important insight into dynamics. In this work we summarize evidence that the T. castaneum structure is Telomerase Reverse Transcriptase. We use this structure to build a partial model of the human Telomerase complex. The model suggests an explanation for the structural role of several diseaseassociated mutations. We then generate a 3D kinematic trajectory of telomere elongation to illustrate a "typewriter" mechanism: the RNA template moves to keep the end of the growing telomeric primer in the active site, disengaging after every 6-residue extension to execute a "carriage return" and go back to its starting position. A hairpin can easily form in the primer, from DNA residues leaving the primer-template duplex. The trajectory is consistent with available experimental evidence. The methodology is extensible to many problems in structural biology in general and personalized medicine in particular.

RNAs need to adopt a specific architecture to exert their task in cells. While significant progress has been made in describing RNA folding landscapes in vitro, understanding intracellular RNA structure formation is still in its infancy. This is in part due to the complex nature of the cellular environment but also to the limited availability of suitable methodologies. To assess the intracellular structure of large RNAs, we recently applied a chemical probing technique and a metal-induced cleavage assay in vivo. These methods are based on the fact that small molecules, like dimethyl sulfate (DMS), or metal ions, such as Pb(2+), penetrate and spread throughout the cell very fast. Hence, these chemicals are able to modify accessible RNA residues or to induce cleavage of the RNA strand in the vicinity of a metal ion in living cells. Mapping of these incidents allows inferring information on the intracellular conformation, metal ion binding sites or ligand-induced structural changes of the respective RNA molecule. Importantly, in vivo chemical probing can be easily adapted to study RNAs in different cell types.

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