18 kDa microtubule-associated protein: identification as a new light chain (LC-3) of microtubule-associated protein 1 (MAP-1)

AbstractSDS gel electrophoresis of microtubule proteins obtained from bovine brain by polymerization cycles revealed a new protein of 18 kDa. This protein was copolymerized with tubulin and its stoichiometry to tubulin remained constant for at least 5 cycles of assembly. Moreover, this protein remained bound to microtubules stabilized with 10 μM taxol and pelleted through a 4 M glycerol cushion. The same 18 kDa protein was found in a purified preparation of the high molecular mass microtubule-associated protein 1 (MAP-1). The 18 kDa protein copurified with the MAP-1 heavy chains during column chromatography on phosphocellulose, DEAE-cellulose, hydroxyapatite and Bio-Gel A-15m. Incubation of the MAP-1 preparation with a mouse monoclonal antibody to the light chain 1 (LC-1) of MAP-1 and with a second precipitating antibody (a rabbit antibody to mouse IgG) immunoprecipitated from the solution all the known components of MAP-1 (heavy chains, LC-1, LC-2), as well as the 18 kDa protein. Immunoblotting showed, however, that this antibody does not interact directly with the 18 kDa protein. These results indicate that the 18 kDa protein forms a complex with all other components of MAP-1. This polypeptide, therefore, is a new light chain (LC-3) of M AP-1

Paradigm lost: milton connects kinesin heavy chain to miro on mitochondria

The kinesin motor typically binds to cargo through its light chains. In this issue Glater et al. (p. 545) demonstrate a new type of linkage through the adapter protein, milton, and the mitochondrial membrane GTPase, miro. This is an important result because it represents a new mechanism of cargo binding and because miro's ability to bind GTP and calcium suggests that it is involved in the regulation of mitochondrial transport

α–E-catenin binds to dynamitin and regulates dynactin-mediated intracellular traffic

α–Epithelial catenin (E-catenin) is an important cell–cell adhesion protein. In this study, we show that α–E-catenin also regulates intracellular traffic by binding to the dynactin complex component dynamitin. Dynactin-mediated organelle trafficking is increased in α–E-catenin−/− keratinocytes, an effect that is reversed by expression of exogenous α–E-catenin. Disruption of adherens junctions in low-calcium media does not affect dynactin-mediated traffic, indicating that α–E-catenin regulates traffic independently from its function in cell–cell adhesion. Although neither the integrity of dynactin–dynein complexes nor their association with vesicles is affected by α–E-catenin, α–E-catenin is necessary for the attenuation of microtubule-dependent trafficking by the actin cytoskeleton. Because the actin-binding domain of α–E-catenin is necessary for this regulation, we hypothesize that α–E-catenin functions as a dynamic link between the dynactin complex and actin and, thus, integrates the microtubule and actin cytoskeleton during intracellular trafficking

Rab32 Regulates Melanosome Transport in Xenopus Melanophores by Protein Kinase A Recruitment

SummaryIntracellular transport is essential for cytoplasm organization, but mechanisms regulating transport are mostly unknown. In Xenopus melanophores, melanosome transport is regulated by cAMP-dependent protein kinase A (PKA) [1]. Melanosome aggregation is triggered by melatonin, whereas dispersion is induced by melanocyte-stimulating hormone (MSH) [2]. The action of hormones is mediated by cAMP: High cAMP in MSH-treated cells stimulates PKA, whereas low cAMP in melatonin-treated cells inhibits it. PKA activity is typically restricted to specific cell compartments by A-kinase anchoring proteins (AKAPs) [3]. Recently, Rab32 has been implicated in protein trafficking to melanosomes [4] and shown to function as an AKAP on mitochondria [5]. Here, we tested the hypothesis that Rab32 is involved in regulation of melanosome transport by PKA. We demonstrated that Rab32 is localized to the surface of melanosomes in a GTP-dependent manner and binds to the regulatory subunit RIIα of PKA. Both RIIα and Cβ subunits of PKA are required for transport regulation and are recruited to melanosomes by Rab32. Overexpression of wild-type Rab32, but not mutants unable to bind PKA or melanosomes, inhibits melanosome aggregation by melatonin. Therefore, in melanophores, Rab32 is a melanosome-specific AKAP that is essential for regulation of melanosome transport

Pavarotti/MKLP1 Regulates Microtubule Sliding and Neurite Outgrowth in Drosophila Neurons

SummaryRecently, we demonstrated that kinesin-1 can slide microtubules against each other, providing the mechanical force required for initial neurite extension in Drosophila neurons. This sliding is only observed in young neurons actively forming neurites and is dramatically downregulated in older neurons. The downregulation is not caused by the global shutdown of kinesin-1, as the ability of kinesin-1 to transport membrane organelles is not diminished in mature neurons, suggesting that microtubule sliding is regulated by a dedicated mechanism [1]. Here, we have identified the “mitotic” kinesin-6 Pavarotti (Pav-KLP) as an inhibitor of kinesin-1-driven microtubule sliding. Depletion of Pav-KLP in neurons strongly stimulated the sliding of long microtubules and neurite outgrowth, while its ectopic overexpression in the cytoplasm blocked both of these processes. Furthermore, postmitotic depletion of Pav-KLP in Drosophila neurons in vivo reduced embryonic and larval viability, with only a few animals surviving to the third instar larval stage. A detailed examination of motor neurons in the surviving larvae revealed the overextension of axons and mistargeting of neuromuscular junctions, resulting in uncoordinated locomotion. Taken together, our results identify a new role for Pav-KLP as a negative regulator of kinesin-1-driven neurite formation. These data suggest an important parallel between long microtubule-microtubule sliding in anaphase B and sliding of interphase microtubules during neurite formation

Regulation of Organelle Movement in Melanophores by Protein Kinase A (PKA), Protein Kinase C (PKC), and Protein Phosphatase 2A (PP2A)

We used melanophores, cells specialized for regulated organelle transport, to study signaling pathways involved in the regulation of transport. We transfected immortalized Xenopus melanophores with plasmids encoding epitope-tagged inhibitors of protein phosphatases and protein kinases or control plasmids encoding inactive analogues of these inhibitors. Expression of a recombinant inhibitor of protein kinase A (PKA) results in spontaneous pigment aggregation. α-Melanocyte-stimulating hormone (MSH), a stimulus which increases intracellular cAMP, cannot disperse pigment in these cells. However, melanosomes in these cells can be partially dispersed by PMA, an activator of protein kinase C (PKC). When a recombinant inhibitor of PKC is expressed in melanophores, PMA-induced pigment dispersion is inhibited, but not dispersion induced by MSH. We conclude that PKA and PKC activate two different pathways for melanosome dispersion. When melanophores express the small t antigen of SV-40 virus, a specific inhibitor of protein phosphatase 2A (PP2A), aggregation is completely prevented. Conversely, overexpression of PP2A inhibits pigment dispersion by MSH. Inhibitors of protein phosphatase 1 and protein phosphatase 2B (PP2B) do not affect pigment movement. Therefore, melanosome aggregation is mediated by PP2A

Classical nonlinear response of a chaotic system: Langevin dynamics and spectral decomposition

We consider the classical response of a strongly chaotic Hamiltonian system. The spectrum of such a system consists of discrete complex Ruelle-Pollicott (RP) resonances which manifest themselves in the behavior of the correlation and response functions. We interpret the RP resonances as the eigenstates and eigenvalues of the Fokker-Planck operator obtained by adding an infinitesimal noise term to the first-order Liouville operator. We demonstrate how the deterministic expression for the linear response is reproduced in the limit of vanishing noise. For the second-order response we establish an equivalence of the spectral decomposition with infinitesimal noise and the long-time asymptotic expansion for the deterministic case.Comment: 16 pages, 1 figur

Multi-Channel Atomic Scattering and Confinement-Induced Resonances in Waveguides

We develop a grid method for multi-channel scattering of atoms in a waveguide with harmonic confinement. This approach is employed to extensively analyze the transverse excitations and deexcitations as well as resonant scattering processes. Collisions of identical bosonic and fermionic as well as distinguishable atoms in harmonic traps with a single frequency $\omega$ permitting the center-of-mass (c.m.) separation are explored in depth. In the zero-energy limit and single mode regime we reproduce the well-known confinement-induced resonances (CIRs) for bosonic, fermionic and heteronuclear collisions. In case of the multi-mode regime up to four open transverse channels are considered. Previously obtained analytical results are extended significantly here. Series of Feshbach resonances in the transmission behaviour are identified and analyzed. The behaviour of the transmission with varying energy and scattering lengths is discussed in detail. The dual CIR leading to a complete quantum suppression of atomic scattering is revealed in multi-channel scattering processes. Possible applications include, e.g., cold and ultracold atom-atom collisions in atomic waveguides and electron-impurity scattering in quantum wires.Comment: 35 pages, 18 figure

Noncommutative Toda Chains, Hankel Quasideterminants And Painlev'e II Equation

We construct solutions of an infinite Toda system and an analogue of the Painlev'e II equation over noncommutative differential division rings in terms of quasideterminants of Hankel matrices.Comment: 16 pp; final revised version, will appear in J.Phys. A, minor changes (typos corrected following the Referee's List, aknowledgements and a new reference added