Biology subjects

Braun, M.

Publications and source records attributed to Braun, M..

43 records · Page 3Linked to original sources

bioRxiv2020

Intrinsically disordered domain of kinesin-3 Kif14 enables unique functional diversity

In addition to their force-generating motor domains, kinesin motor proteins feature various accessory domains enabling them to fulfil a variety of functions in the cell. Human kinesin-3, Kif14, localizes to the midbody of the mitotic spindle and is involved in the progression of cytokinesis. The specific motor properties enabling Kif14s cellular functions, however, remain unknown. Here, we show in vitro that it is the intrinsically disordered N-terminal domain of Kif14 that enables unique functional diversity of the motor. Using single molecule TIRF microscopy we observed that the presence of the disordered domain i) increased the Kif14 run-length by an order of magnitude, rendering the motor super-processive and enabling the motor to pass through highly crowded microtubule areas shielded by cohesive layers of microtubule-associated protein tau, which blocks less processive motors ii) enabled robust, autonomous Kif14 tracking of growing microtubule tips, independent of microtubule end-binding (EB) proteins and iii) enabled Kif14 to crosslink parallel microtubules and to drive the relative sliding of antiparallel ones. We explain these features of Kif14 by the observed increased affinity of the disordered domain for GTP-like tubulin and the observed diffusible interaction of the disordered domain with the microtubule lattice. We hypothesize that the disordered domain tethers the motor domain to the microtubule forming a diffusible foothold. We suggest that the intrinsically disordered N-terminal anchoring domain of Kif14 is a regulatory hub supporting the various cellular functions of Kif14 by tuning the motors interaction with microtubules.

biophysics↗

bioRxiv2020

Anillin propels myosin-independent constriction of actin rings

Constriction of the actin cytokinetic ring is an essential step of cell division. In a generally accepted view, the constriction is driven by relative sliding of actin filaments propelled by myosin motors. However, in multiple organisms, the ring constriction is myosin independent. How actin rings constrict in the absence of motor activity remains unclear. Here, we demonstrate that actin contractility can be propelled by anillin, a diffusible non-motor actin crosslinker, localising to the cytokinetic ring. We in vitro observed the formation and constriction of rings comprising multiple actin filaments bundled by anillin. Rings constricted due to anillin-generated forces maximising the overlap lengths between the filaments. Actin disassembly promoted constriction. We propose that actin crosslinkers, generating forces complementary to molecular motors, contribute to the contractility of diverse actin structures, including the cytokinetic ring.

cell biology↗

bioRxiv2020

Mitochondria-adaptor TRAK1 promotes kinesin-1 driven transport in crowded environments

Intracellular trafficking of organelles, driven by kinesin-1 stepping along microtubules, underpins essential processes including neuronal activity. In absence of other proteins on the microtubule surface, kinesin-1 performs micron-long runs. Under protein crowding conditions, however, kinesin-1 motility is drastically impeded. It is thus unclear how kinesin-1 acts as an efficient transporter in crowded intracellular environments. Here, we demonstrate that TRAK1 (Milton), an adaptor protein essential for mitochondrial trafficking, activates kinesin-1 and increases its robustness of stepping in protein crowding conditions. Interaction with TRAK1 i) facilitated kinesin-1 navigation around obstacles, ii) increased the probability of kinesin-1 passing through cohesive envelopes of tau and iii) increased the run length of kinesin-1 in cell lysate. We explain the enhanced motility by the observed direct interaction of TRAK1 with microtubules, providing an additional anchor for the kinesin-1-TRAK1 complex. We propose adaptor-mediated tethering as a mechanism regulating kinesin-1 motility in various cellular environments.

cell biology↗

bioRxiv2019

De-novo variants in XIRP1 associated with polydactyly and polysyndactyly in Holstein cattle

Congenital polydactylous cattle are sporadically observed. Impairment of the limb patterning process due to altered control of the zone of polarizing activity (ZPA) was associated in several species with preaxial polydactyly and syndactyly. In cattle, the role of ZPA and other genes involved in limb patterning for polydactyly was not yet elucidated. Herein, we report on a preaxial type II polydactyly and a praeaxial type II+V polysyndactyly in two Holstein calves and screen whole genome sequencing data for associated variants. Using whole genome sequencing data of both affected calves did not show mutations in the candidate regions of ZRS and pZRS or in candidate genes associated with polydactyly, syndactyly and polysyndactyly in other species. Two indels, which are located in XIRP1 within a common haplotype, were highly associated with the two phenotypes. Bioinformatic analyses retrieved an interaction between XIRP1 and FGFR1, CTNNB1 and CTNND1 supporting a link between the XIRP1 variants and embryonic limb patterning. The heterozygous haplotype was highly associated with the present polydactylous phenotypes due to dominant mode of inheritance with an incomplete penetrance in Holstein cattle.

genetics↗

bioRxiv2019

A large self-transmissible plasmid from Nigeria confers resistance to multiple antibacterials without a carrying cost

Antimicrobial resistance is rapidly expanding, in a large part due to mobile genetic elements. We screened 94 fecal fluoroquinolone-resistant Escherichia coli isolates from Nigeria for six plasmid-mediated quinolone resistance (PMQR) genes. Sixteen isolates harbored at least one of the PMQR genes and four were positive for aac-6-Ib-cr. In one strain, aac-6-Ib-cr was mapped to a 125 Kb self-transmissible IncFII plasmid, pMB2, which also bears blaCTX-M-15, seven other functional resistance genes and multiple resistance pseudogenes. We hypothesized that pMB2 had been selected by antimicrobials and that its large size would confer a growth disadvantage. However, laboratory strains carrying pMB2 grew at least as fast as isogenic strains lacking the plasmid in both rich and minimal media. We excised a 32 Kb fragment containing the sitABCD and another putative transporter, pefB, a papB homolog, and several open-reading frames of unknown function. The resulting 93 Kb mini-plasmid conferred slower growth rates and lower fitness than wildtype pMB2. Trans-complementing the deletion with the cloned sitABCD genes confirmed that they accounted for the growth advantage conferred by pMB2 in iron-depleted media. The mini-plasmid additionally conferred autoaggregation and was less transmissible and both phenotypes could be complemented with a pefB clone. pMB2 is a large plasmid with a flexible resistance region that contains multiple loci that can account for evolutionary success in the absence of antimicrobials. Ancillary functions conferred by resistance plasmids can mediate their retention and transmissibility, worsening the trajectory for antimicrobial resistance and potentially circumventing efforts to contain resistance through restricted use.

microbiology↗

bioRxiv2018

Kinetically distinct phases of tau on microtubules regulate kinesin motors and severing enzymes

Tau is an intrinsically disordered protein, which diffuses on microtubules. In neurodegenerative diseases collectively termed tauopathies, tau malfunction and its detachment from axonal microtubules is correlated with microtubule degradation. It is known that tau can protect microtubules from microtubule-degrading enzymes, such as katanin. However, how tau can fulfill such regulative function is still unclear. Using in vitro reconstitution, we here show that tau molecules on microtubules cooperatively form islands of an ordered layer with regulatory qualities distinct from a comparably dense layer of diffusible tau. These islands shield the microtubules from katanin and kinesin-1 but are penetrable by kinesin-8 which causes the islands to disassemble. Our results indicate a new phase of tau, constituting an adjustable protective sheath around microtubules.

biophysics↗

bioRxiv2017

Local Nucleation Of Microtubule Bundles Through Tubulin Concentration Into A Condensed Tau Phase

Non-centrosomal microtubule bundles play important roles in cellular organization and function. Although many diverse proteins are known that can bundle microtubules, biochemical mechanisms by which cells could locally control the nucleation and formation of microtubule bundles are understudied. Here, we demonstrate that concentration of tubulin into a condensed, liquid-like compartment composed of the unstructured neuronal protein tau is sufficient to nucleate microtubule bundles. We show that under conditions of macro-molecular crowding, tau forms liquid drops. Tubulin partitions into these drops, efficiently increasing tubulin concentration and driving the nucleation of microtubules. These growing microtubules form bundles enclosed in a liquid sheath of tau. Our data suggest that condensed compartments of microtubule bundling proteins could promote the local formation of microtubule bundles in neurons by acting as non-centrosomal microtubule nucleation centers, and that liquid-like tau encapsulation could provide both stability and plasticity to long axonal microtubule bundles.

cell biology↗