Interaction of CDK5RAP2 with EB1 to Track Growing Microtubule Tips and to Regulate Microtubule Dynamics

Mutations in cdk5rap2 are linked to autosomal recessive primary microcephaly, and attention has been paid to its function at centrosomes. In this report, we demonstrate that CDK5RAP2 localizes to microtubules and concentrates at the distal tips in addition to centrosomal localization. CDK5RAP2 interacts directly with EB1, a prototypic member of microtubule plus-end tracking proteins, and contains the basic and Ser-rich motif responsible for EB1 binding. The EB1-binding motif is conserved in the CDK5RAP2 sequences of chimpanzee, bovine, and dog but not in those of rat and mouse, suggesting a function gained during the evolution of mammals. The mutation of the Ile/Leu-Pro dipeptide within the motif abolishes EB1 interaction and plus-end attachment. In agreement with the mutational analysis, suppression of EB1 expression inhibits microtubule tip-tracking of CDK5RAP2. We have also found that the CDK5RAP2-EB1 complex regulates microtubule dynamics and stability. CDK5RAP2 depletion by RNA interference impacts the dynamic behaviors of microtubules. The CDK5RAP2-EB1 complex induces microtubule bundling and acetylation when expressed in cell cultures and stimulates microtubule assembly and bundle formation in vitro. Collectively, these results show that CDK5RAP2 targets growing microtubule tips in association with EB1 to regulate microtubule dynamics

Electronic Spectra of Cs<inf>2</inf>NaYb(NO<inf>2</inf>)<inf>6</inf>: Is There Quantum Cutting?

© 2018 American Chemical Society. The crystal structure and electronic spectra of the Th symmetry hexanitritoytterbate(III) anion have been studied in Cs2NaY0.96Yb0.04(NO2)6, which crystallizes in the cubic space group Fm3. The emission from Yb3+ can be excited via the NO2- antenna. The latter electronic transition is situated at more than twice the energy of the former, but at room temperature, one photon absorbed at 470 nm in the triplet state produces no more than one photon emitted. Some degree of quantum cutting is observed at 298 K under 420 nm excitation into the singlet state and at 25 K using excitation into either state. The quantum efficiency is ∼10% at 25 K. The energy level scheme of Yb3+ has been deduced from excitation and emission spectra and calculated by crystal field theory. New improved energy level calculations are also reported for the Cs2NaLn(NO2)6 (Ln = Pr, Eu, Tb) series using the f-Spectra package. The neat crystal Cs2NaYb(NO2)6 has also been studied, but results were unsatisfactory due to sample decomposition, and this chemical instability makes it unsuitable for applications

Electronic Spectra of Cs₂NaYb(NO₂)₆: Is There Quantum Cutting?

The crystal structure and electronic spectra of the <i>T</i>_<i>h</i> symmetry hexanitritoytterbate­(III) anion have been studied in Cs₂NaY_0.96Yb_0.04(NO₂)₆, which crystallizes in the cubic space group <i>Fm</i>3̅. The emission from Yb³⁺ can be excited via the NO₂^– antenna. The latter electronic transition is situated at more than twice the energy of the former, but at room temperature, one photon absorbed at 470 nm in the triplet state produces no more than one photon emitted. Some degree of quantum cutting is observed at 298 K under 420 nm excitation into the singlet state and at 25 K using excitation into either state. The quantum efficiency is ∼10% at 25 K. The energy level scheme of Yb³⁺ has been deduced from excitation and emission spectra and calculated by crystal field theory. New improved energy level calculations are also reported for the Cs₂NaLn­(NO₂)₆ (Ln = Pr, Eu, Tb) series using the <i>f</i>-<i>Spectra</i> package. The neat crystal Cs₂NaYb­(NO₂)₆ has also been studied, but results were unsatisfactory due to sample decomposition, and this chemical instability makes it unsuitable for applications