Biology subjects

Rudiger, S. G. D.

Publications and source records attributed to Rudiger, S. G. D..

5 recordsLinked to original sources

bioRxiv2018

Human chaperones untangle fibrils of the Alzheimer protein Tau

Alzheimers Disease is the most common neurodegenerative disorder. A hallmark of this disease is aggregation of the protein Tau into fibrillar tangles, which is ultimately linked to neuronal death 1,2. Oligomeric precursors of Tau fibrils are suspected to be the neurotoxic agent while fibrils themselves may be less harmful end products of the aggregation process 3,4. Evolutionary conserved families of molecular chaperones maintain protein homeostasis in healthy cells, preventing aggregation 5,6. Here, we investigate whether such chaperones could possibly reverse the aggregation reaction and dissolve Tau fibrils. Indeed we find that the human Hsp70 chaperone system disaggregates Tau fibrils. Both the bacterial and human Hsp70 chaperone systems disassemble fibril superstructures assembled of several fibril strands into single fibrils, indicating that this is an evolutionary conserved capacity of the Hsp70 system. However, further disaggregation of Tau fibrils into oligomers and even monomers is reserved to the human homologue. Thus, although bacteria possess an effective machinery to dissolve amorphous aggregates 7-9, we see that they do not have the means to disaggregate fibrils. Fibrillar aggregates, therefore, require different chaperone systems than amorphous aggregates, and this is a property acquired by Hsp70 during evolution. This makes the Hsp70 system an interesting target for novel drug strategies in Alzheimer.

biochemistry↗

bioRxiv2018

MAP7 family proteins are microtubule-tethered allosteric activators of kinesin-1.

Kinesin-1 is responsible for microtubule-based transport of numerous cellular cargoes. Here, we explored the regulation of kinesin-1 by MAP7 proteins. We found that all four mammalian MAP7 family members bind to kinesin-1. In HeLa cells, MAP7, MAP7D1 and MAP7D3 act redundantly to enable kinesin-1-dependent transport and microtubule recruitment of the truncated kinesin-1 KIF5B-560, which contains the stalk but not the cargo-binding and autoregulatory regions. In vitro, purified MAP7 and MAP7D3 increase microtubule landing rate and processivity of kinesin-1 through transient association with the motor. MAP7 proteins promote binding of kinesin-1 to microtubules both directly, through the N-terminal microtubule-binding domain and unstructured linker region, and indirectly, through an allosteric effect exerted by the kinesin-binding C-terminal domain. Compared to MAP7, MAP7D3 has a higher affinity for kinesin-1 and a lower affinity for microtubules and, unlike MAP7, can be co-transported with the motor. We propose that MAP7 proteins are microtubule-tethered kinesin-1 activators, with which the motor transiently interacts as it moves along microtubules.\n\nSummaryA combination of experiments in cells and in vitro reconstitution assays demonstrated that mammalian MAP7 family proteins act redundantly to activate kinesin-1 and promote its microtubule binding and processivity by transiently associating with the stalk region of the motor.

cell biology↗

bioRxiv2017

Successful aggregation of Tau protein labelled on its native cysteines

The formation of fibrillar tangles of the Tau protein is crucial in the development of Alzheimers disease. Biophysical methods based on labelling of the cysteines of Tau with fluorescence dyes would allow to study fibril formation with an internal eye. However, the two native cysteines of Tau at positions 291 and 322 are located in the repeat domain, which is involved in forming the fibrils. The contribution of both cysteines to this process is unclear. Here we show that blocking natural cysteines using large fluorescent dyes does not interfere with Tau fibrillation so that FRET can be used to follow structural changes during the process. We anticipate that cysteine-labelled Tau enables following structural rearrangements during fibril formation in detail. This may also allow to monitor the effect of drugs, small molecules and proteins on the process.

biochemistry↗

bioRxiv2017

Breaking the Deadlock of Molecular Chaperones

Protein folding in the cell requires ATP-driven chaperone machines. It is poorly understood, however, how these machines fold proteins. Here we propose that the conserved Hsp70 and Hsp90 chaperones support formation of the folding nucleus by providing a gradient of decreasing hydrophobicity. Early on the folding pathway Hsp70 uses its highly hydrophobic binding pocket to recover a stalled, unproductive folding intermediate. The aggressive nature of Hsp70 action, however, blocks productive folding by grabbing hydrophobic, core-forming segments. This precludes on-pathway nucleation at high, physiological Hsp70 levels. Transfer to the less hydrophobic Hsp90 enables the intermediate to resume forming its folding nucleus. Subsequently, the protein enters a spontaneous folding trajectory towards its native state, independent of the ATPase activities of both Hsp70 and Hsp90. Our findings provide a general mechanistic concept for chaperoned protein folding.

biochemistry↗

bioRxiv2017

Production and purification of human Hsp90β in Escherichia coli

The molecular chaperone Hsp90 is an essential member of the cellular proteostasis system. It plays an important role in the stabilisation and activation of a large number of client proteins and is involved in fatal disease processes e.g. Alzheimer disease, cancer and cystic fibrosis. This makes Hsp90 a crucial protein to study. Mechanistic studies require large amounts of protein but the production and purification of recombinant human Hsp90 in E. coli is challenging and laborious. Here we identified conditions that influence Hsp90 production and optimised a fast and efficient purification protocol. We found that the nutrient value of the culturing medium and the length of induction had significant effect on Hsp90 production in Escherichia coli. Our fast, single-day purification protocol resulted in a stable, well-folded and pure sample that was resistant to degradation in a reproducible manner. We anticipate that our results provide a useful tool to produce higher amount of pure, well-folded and stable recombinant human Hsp90{beta} in Escherichia coli in an efficient way.

biochemistry↗