No abstract

Structural evolution from monomer to fibril of amyloid β peptide is related to pathogenic mechanism of Alzheimer disease, and its acceleration is a long-running problem in drug development. This study reveals that ultrasonic cavitation bubbles behave as catalysts for nucleation of the peptide: The nucleation reaction is highly dependent on frequency and pressure of acoustic wave, and we discover an optimum acoustical condition, at which the reaction-rate constant for nucleation is increased by three-orders-of magnitudes. A theoretical model is proposed for explaining highly frequency and pressure dependent nucleation reaction, where monomers are captured on the bubble surface during its growth and highly condensed by subsequent bubble collapse, so that they are transiently exposed to high temperatures. Thus, the dual effects of local condensation and local heating contribute to dramatically enhance the nucleation reaction. Our model consistently reproduces the frequency and pressure dependences, supporting its essential applicability.

Background: Katanin p60 is a protein that actively severs microtubules. Results: Mutations within the AAAϩ pore of katanin p60 and in the C-terminal regions of tubulins perturb efficient microtubule severing. Conclusion: Interactions between the conserved residues in the katanin p60 pore and the acidic tails of both tubulins may be important. Significance: Both tubulin molecules are essential for microtubule severing by katanin.

Interaction between monomer peptides and seeds is essential for clarifying the fibrillation mechanism of amyloid β (Aβ) peptides. We monitored the deposition reaction of Aβ1–40 peptides on immobilized seeds grown from Aβ1–42, which caused formation of oligomers in the early stage. The deposition reaction and fibrillation procedure were monitored throughout by novel total-internal-reflection-fluorescence microscopy with a quartz-crystal microbalance (TIRFM-QCM) system. This system allows simultaneous evaluation of the amount of deposited peptides on the surface seeds by QCM and fibril nucleation and elongation by TIRFM. Most fibrils reached other nuclei, forming the fibril network across the nucleus hubs in a short time. We found a fibril-elongation rate two-orders-of-magnitude higher in an oligomeric cloud than reported values, indicating ultrafast transition of oligomers into fibrils.

p97 (also called VCP and CDC-48) is an AAA+ chaperone, which consists of a substrate/cofactor-binding N domain and two ATPase domains (D1 and D2), and forms a homo-hexameric ring. p97 plays crucial roles in a variety of cellular processes such as the ubiquitin-proteasome pathway, the endoplasmic reticulum-associated protein degradation, autophagy, and modulation of protein aggregates. Mutations in human p97 homolog VCP are linked to neurodegenerative diseases. The key mechanism of p97 in these various functions has been proposed to be the disassembly of protein complexes. To understand the molecular mechanism of p97, we studied the conformational changes of hexameric CDC-48.1, a Caenorhabditis elegans p97 homolog, using high-speed atomic force microscopy. In the presence of ATP, the N-D1 ring repeatedly rotates ~23 ± 8° clockwise and resets relative to the D2 ring. Mutational analysis reveals that this rotation is induced by ATP binding to the D2 domain.

Graphical abstract

Label-free biosensors, including conventional quartz-crystal-microbalance (QCM) biosensor, are seriously affected by nonspecific adsorption of contaminants involved in analyte solution, and it is exceptionally difficult to extract the sensor responses caused only by the targets. In this study, we reveal that this difficulty can be overcome with an ultrahigh-frequency wireless QCM biosensor. The sensitivity of a QCM biosensor dramatically improves by thinning the quartz resonator, which also makes the resonance frequency higher, causing high-speed surface movement. Contaminants weakly (nonspecifically) interact with the quartz surface, and they fail to follow the fast surface movement and cannot be detected as the loaded mass. The targets are, however, 1 tightly captured by the receptor proteins immobilized on the surface, and they can move with the surface, contributing to the loaded mass and decreasing the resonant frequency. We develop a MEMS QCM biosensor, in which an AT-cut quartz resonator of 26 µm thick is packaged without fixing, and demonstrate this phenomenon by comparing the frequency changes of fundamental (∼64 MHz) and ninth (∼576 MHz) modes.At ultrahigh-frequency operation with the ninth mode, the sensor response is independent of the amount of impurity proteins, and the binding affinity is unchanged. We then applied this method for the label-free and sandwich-free direct detection of C-reactive protein (CRP) in serum, and confirmed its applicability.

No abstract