JCB

New issue: November 28th

In today's new issue of JCB, Wen et al. reveal that the development of Alzheimer's disease might be promoted by defective recycling of the enzyme beta-secretase. Vps35 is a component of the retromer complex that transports proteins from endosomes to the Golgi. In the absence of Vps35, cells accumulate extra beta-secretase in their endosomes, where the enzyme may be more active in converting amyloid precursor protein into toxic Abeta peptides. Mice prone to Alzheimer's disease develop neurodegenerative symptoms even quicker if they lack one copy of the VPS35 gene. You can read more in this summary.

Calvert et al. find that large cells divide at a faster rate than small cells in the filamentous fungus Neurospora crassa. The reason seems to be that larger cells start off with a higher amount of myosin II in the contractile ring that separates cells during cytokinesis, which allows the rings to constrict more rapidly. More here.

Karotki et al. demonstrate that the components of eisosomes - protein complexes that spatially organize the plasma membrane - carry out their function by assembling into a lipid-binding filamentous scaffold. As explained in this week's In Focus, Karotki et al. show that, in vitro, eisosome proteins assemble into helical filaments that can re-shape artificial liposomes, suggesting that the proteins may act similarly to remodel the plasma membrane. Indeed, this issue's cover image shows a helical eisosome filament on the cytoplasmic face of the budding yeast plasma membrane.

Lasserre et al. describe how the kinase HPK1 phosphorylates two signaling adaptor proteins in order to disassembly T cell receptor microclusters and switch off T cell signaling. (Summary here). And, sticking with T cells, Zyss et al. reveal that casein kinase I delta helps to reposition the centrosome toward the immunological synapse (where T-lymphocytes contact their target, antigen-presenting cells), perhaps by working with the microtubule plus-end binding protein EB1 to regulate microtubule growth. You can find out more in this month's biosights, in which senior author Fanni Gergely explains CK1 delta's role in centrosome translocation in more detail...

Lots more interesting papers that I didn't have time to mention here. You can find them all on our table of contents by clicking this link.

 

 

 

New issue: November 14th

Here’s a few quick highlights from the new issue of JCB…

Krementsova et al. describe how the budding yeast myosin Myo4 gains the ability to walk along actin fibers only when coupled to its mRNA cargo. Unlike many other myosin motors, Myo4 is normally monomeric, and is therefore unable to take processive steps along actin by itself. But Krementsova et al. show that the mRNA-binding protein She2 recruits two Myo4 molecules, allowing the complex to walk “hand-over-hand” along actin cables, just like regular myosin dimers. You can read more in this summary.

Morin-Leisk et al. investigate the function of atlastin, a GTPase that drives the tethering and fusion of ER membrane tubules, thereby helping the ER network to maintain a branched morphology. Morin-Leisk et al. identify an intramolecular salt bridge essential for a conformational change in atlastin that is thought to promote membrane fusion. Moreover, the researchers provide evidence that this conformational change isn’t driven by GTP hydrolysis, which, says senior author Tina Lee, raises the question of which step in membrane fusion is dependent on atlastin’s catalytic activity.

Pigino et al. use cryoelectron tomography to reveal the three-dimensional structure of radial spokes, key regulatory complexes that determine how cilia and flagella move. (You can see these structures – colored red – on the journal’s cover). By comparing various mutant strains of Chlamydomonas, the researchers were able to assign many of the 23 proteins that form the spokes to specific locations within these structures and, as explained in this summary, Pigino et al.’s results support the idea that the radial spokes assemble through the dimerization of smaller, precursor structures.

Meanwhile, two papers reveal that there’s much more of the centromeric protein CENP-A at budding yeast centromeres than previously thought. CENP-A is a histone H3 variant that marks centromeric chromatin, and it had been assumed that there were only two copies of the protein at every centromere in budding yeast. But Coffman et al. and Lawrimore et al. now show that there’s between 5 and 8 copies of CENP-A per centromere. Because CENP-A has previously been used as a standard to count the relative numbers of kinetochore proteins, the new estimate means that kinetochore proteins are 3-4 times more abundant than previously estimated, which, as Ted Salmon explains in this week’s In Focus, helps explain how these complexes attach to spindle microtubules during mitosis.

And finally for today, Specht et al. describe how the small heat shock protein Hsp42 helps to deposit misfolded proteins at specific locations within budding yeast cells. You can learn more in this month’s biobytes podcast, where you’ll also hear Charles Streuli explain his lab’s recent publication (Wang et al.), describing how integrin-based focal adhesions control cell proliferation.

There are lots of other great papers to discover in our new issue.You can find them all on our table of contents by clicking here. 

Cover image courtesy of Pigino et al.