RESUMEN
The dynamics of self-propelled micro-motors, in a thin fluid film containing an attractive substrate, is investigated by means of a particle-based simulation. A chemically powered sphere dimer, consisting of a catalytic and a noncatalytic sphere, may be captured by a trap on the substrate and consequently rotates around the trap center. A pair of trapped dimers spontaneously forms various configurations, including anti-parallel aligned doublets and head-to-tail rotating doublets. Small traps randomly distributed on the substrate are capable of pinning the dimers. The diffusion coefficient decreases with increasing pinning force or the pinning density, and it falls quickly at a certain critical pinning force beyond which the dimer motor is pinned completely. It is found that the pin array on the substrate gives rise to the formation of clusters of dimers and the underlying mechanism is discussed.
RESUMEN
Amyloid precursor protein (APP) mutations associated with familial Alzheimer's disease (AD) usually lead to increases in amyloid ß-protein (Aß) levels or aggregation. Here, we identified a novel APP mutation, located within the Aß sequence (Aß(D7H)), in a Taiwanese family with early onset AD and explored the pathogenicity of this mutation. Cellular and biochemical analysis reveal that this mutation increased Aß production, Aß42/40 ratio and prolonged Aß42 oligomer state with higher neurotoxicity. Because the D7H mutant Aß has an additional metal ion-coordinating residue, histidine, we speculate that this mutation may promote susceptibility of Aß to ion. When co-incubated with Zn(2+) or Cu(2+), Aß(D7H) aggregated into low molecular weight oligomers. Together, the D7H mutation could contribute to AD pathology through a "double punch" effect on elevating both Aß production and oligomerization. Although the pathogenic nature of this mutation needs further confirmation, our findings suggest that the Aß N-terminal region potentially modulates APP processing and Aß aggregation, and further provides a genetic indication of the importance of Zn(2+) and Cu(2+) in the etiology of AD.