Langer, J. D. | bioRxiv Science

bioRxiv2019

Monosomes actively translate synaptic mRNAs in neuronal processes

In order to deal with their huge volume and complex morphology, neurons localize mRNAs and ribosomes near synapses to produce proteins locally. A relative paucity of polyribosomes (considered the active sites of translation) detected in electron micrographs of neuronal processes (axons and dendrites), however, has suggested a rather limited capacity for local protein synthesis. Polysome profiling together with ribosome footprinting of microdissected synaptic regions revealed that a surprisingly high number of dendritic and/or axonal transcripts were predominantly associated with monosomes (single ribosomes). Contrary to prevailing views, the neuronal monosomes were in the process of active protein synthesis (e.g. they exhibited elongation). Most mRNAs showed a similar translational status in both compartments, but some transcripts exhibited differential ribosome occupancy in the somata and neuropil. Strikingly, monosome-preferred transcripts often encoded high-abundance synaptic proteins. This work suggests a significant contribution of monosome translation to the maintenance of the local neuronal proteome. This mode of translation can presumably solve some of restricted space issues (given the large size of polysomes) and also increase the diversity of proteins made from a limited number of ribosomes available in dendrites and axons.

neuroscience↗

bioRxiv2019

Rotary substates of mitochondrial ATP synthase reveal the basis of flexible F1-Fo coupling

F1Fo-ATP synthases play a central role in cellular metabolism, making the energy of the proton-motive force across a membrane available for a large number of energy-consuming processes. We determined the single-particle cryo-EM structure of active dimeric ATP synthase from mitochondria of Polytomella sp. at 2.7- 2.8 [A] resolution. Separation of 13 well-defined rotary substates by 3D classification provides a detailed picture of the molecular motions that accompany c-ring rotation and result in ATP synthesis. Crucially, the F1 head rotates along with the central stalk and c-ring rotor for the first ~30{degrees} of each 120{degrees} primary rotary step. The joint movement facilitates flexible coupling of the stoichiometrically mismatched F1 and Fo subcomplexes. Flexibility is mediated primarily by the interdomain hinge of the conserved OSCP subunit, a well-established target of physiologically important inhibitors. Our maps provide atomic detail of the c-ring/a-subunit interface in the membrane, where protonation and deprotonation of c-ring cGlu111 drives rotary catalysis. An essential histidine residue in the lumenal proton access channel binds a strong non-peptide density assigned to a metal ion that may facilitate c-ring protonation, as its coordination geometry changes with c-ring rotation. We resolve ordered water molecules in the proton access and release channels and at the gating aArg239 that is critical in all rotary ATPases. We identify the previously unknown ASA10 subunit and present complete de novo atomic models of subunits ASA1-10, which make up the two interlinked peripheral stalks that stabilize the Polytomella ATP synthase dimer.

biochemistry↗