In today’s new issue of JCB, Cherepanova et al. describe how an oxidoreductase enzyme promotes the glycosylation of newly synthesized proteins in the ER. MagT1, which contains a thioredoxin-like catalytic domain and is mutated in patients with X-linked mental retardation, associates with an oligosaccharyltransferase complex to facilitate access to N-glycosylation sites that would otherwise be obscured by the formation of disulfide bonds during protein folding. More here.
Pichlo et al. reveal how sea urchin sperm detect and respond to single molecules of chemoattractant as they navigate toward the egg. The researchers find that 300,000 copies of the guanylyl cyclase chemoreceptor are densely packed into the sperm flagellum. These chemoreceptors bind to the chemoattractant with extremely high affinity, but the sperm dial down their sensitivity when they experience higher chemoattractant concentrations nearer the egg so that the receptors don’t become saturated. As explained here, the researchers also describe how the receptors are quickly deactivated after binding to the chemoattractant.
Fernandes and Schöck reveal that Lasp, a much shorter version of the giant vertebrate protein nebulin, regulates the architecture of Drosophila muscle sarcomeres. Vertebrate nebulin contains 185 actin-binding repeats and helps to regulate the length of muscle thin filaments. As summarized here, Lasp performs a similar function in flies, despite the fact that it contains just two nebulin repeats, each of which appears to have a slightly different function in the maintenance of sarcomeric structure.
Cai et al. demonstrate how cells restrict the phosphoinositide PtdIns4P to the trans-Golgi network. After determining the crystal structure of the PtdIns4P-binding protein Vps74 bound to the phosphoinositide phosphatase Sac1, the researchers identified mutations that specifically inhibit the interaction between these two proteins and examined their effect on PtdIns4P distribution and Golgi function. As discussed in this week’s In Focus, the results suggest that Vps74 acts as a membrane receptor for Sac1, recruiting the phosphatase to hydrolyze PtdIns4P in early Golgi compartments such as the medial cisternae and thereby maintaining the identity and function of the trans-Golgi network.
And Edens and Levy describe how Protein Kinase C helps to shrink interphase nuclei during Xenopus embryonic development. Senior author Daniel Levy discusses his lab’s findings in this month’s biobytes podcast, where you can also listen to Kara Helmke describe how the microtubule-binding protein TPX2 controls the size of Xenopus meiotic spindles. You can listen below or subscribe in iTunes.
That’s all for today, but, as always, you can find our full table of contents here. Which papers are you most interested to read?
Cover image of myofibrils from wild-type (top) and Lasp-deficient (bottom) flies © 2014 Fernandes and Schöck.