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33 p.-3 fig. ; During the last decade, the complement field has experienced outstanding advancements in the mechanistic understanding of how complement activators are recognized, what C3 activation means, how protein complexes like the C3 convertases and the membrane attack complex are assembled, and how positive and negative complement regulators perform their function. All of this has been made possible mostly because of the contributions of structural biology to the study of the complement components. The wealth of novel structural data has frequently provided support to previously held knowledge, but often has added alternative and unexpected insights into complement function. Here we will review some of these findings focusing in the alternative and terminal complement pathways. ; SRdeC is supported by the Spanish "Ministerio de Economía y Competitividad-FEDER" (SAF2015-66287R), the Seventh Framework Programme European Union Project EURenOmics (305608) and the Autonomous Region of Madrid (S2010/BMD- 2316). SRdeC is member of the "CIB intramural Program "Molecular Machines for Better Life (MACBET)". EGdeJ is supported by the Spanish "Ministerio de Economía y Competitividad-FEDER" (RYC-2013-13395 and SAF2014-52339P). OL is supported by the Spanish Ministry of Economy, Industry and Competitiveness (SAF2014-52301-R).AT and MS are supported by the Spanish "Ministerio de Economía y Competitividad-FEDER" (IJCI-2015-25222 and IJCI-2015-24388, respectively). ; Peer reviewed

ubulin proteostasis is regulated by a group of molecular chaperones termed tubulin cofactors (TBC). Whereas tubulin heterodimer formation is well-characterized biochemically, its dissociation pathway is not clearly understood. Here, we carried out biochemical assays to dissect the role of the human TBCE and TBCB chaperones in α-tubulin-β-tubulin dissociation. We used electron microscopy and image processing to determine the three-dimensional structure of the human TBCE, TBCB and α-tubulin (αEB) complex, which is formed upon α-tubulin-β-tubulin heterodimer dissociation by the two chaperones. Docking the atomic structures of domains of these proteins, including the TBCE UBL domain, as we determined by X-ray crystallography, allowed description of the molecular architecture of the aEB complex. We found that heterodimer dissociation is an energy-independent process that takes place through a disruption of the α-tubulin-β-tubulin interface that is caused by a steric interaction between b-tubulin and the TBCE cytoskeleton-associated protein glycine-rich (CAP-Gly) and leucine-rich repeat (LRR) domains. The protruding arrangement of chaperone ubiquitin-like (UBL) domains in the aEB complex suggests that there is a direct interaction of this complex with the proteasome, thus mediating α-tubulin degradation. © 2015. Published by The Company of Biologists Ltd. ; This work was supported by the Spanish Ministry of Science and Innovation [grant numbers CONSOLIDER CSD 2006‐23 to M.C., J.C.Z. and J.M.V., BFU2011‐22588 to M.C., BFU2011‐25090 to J.M.B., BFU2013‐44202 to J.M.V., and BFU2010‐18948 to J.C.Z.]; the Madrid Regional Government [grant number S2013/MIT‐2807 to J.M.V.]; the Generalitat de Catalunya [grant number SGR2009‐1309 to M.C.]; the Instituto de Investigación Marqués de Valdecilla (IDIVAL); the Universidad de Cantabria [grant number 02.VP01.64005 to J.C.Z.]; and the European Commission FP7 Cooperation Project SILVER ‐ GA [grant number 260644 to M.C.] ; Peer Reviewed

25 p.- 9 fig.-7 fig. supl.-4 tab. supl. ; The structure of the unique bacterial tubulin BtubA/B from Prosthecobacter is very similar to eukaryotic alphabeta-tubulin, but strikingly, BtubA/B fold without eukaryotic chaperones. Our sequence comparisons indicate that BtubA and BtubB do not really correspond to either alpha or beta-tubulin but have mosaic sequences with intertwining features from both. Their nucleotide binding loops are more conserved and their more divergent sequences correspond to discrete surface zones of tubulin involved in microtubule assembly and binding to eukaryotic chaperonin CCT, which is absent from the P. dejongeii draft genome. BtubA/B cooperatively assembles over a wider range of conditions than alphabeta-tubulin, forming pairs of protofilaments which coalesce into bundles instead of microtubules, and it lacks the abilities to differentially interact with divalent cations and bind typical tubulin drugs. Assembled BtubA/B contain close to one bound GTP and GDP. Both BtubA and BtubB subunits hydrolyze GTP, leading to disassembly. The mutant BtubA/B-S144G in the tubulin signature motif GGG(T/S)G(S/T)G has strongly inhibited GTPase, but BtubA-T147G/B does not, suggesting that BtubB is a more active GTPase, like beta-tubulin. BtubA/B chimera bearing the beta-tubulin loops M, H1-S2 and S9-S10 in BtubB fold, assemble and have reduced GTPase. However, introduction of the alpha-tubulin loop S9-S10 with its unique 8-residue insertion impaired folding. From the sequence analyses, its primitive assembly features and the properties of the chimeras, we propose that BtubA/B were acquired shortly after duplication of a spontaneously folding alpha and beta-tubulin ancestor, possibly by horizontal gene transfer from a primitive eukaryotic cell, followed by divergent evolution ; This work was supported in part by Ministerio de Ciencia e Innovación Grants BFU2008-00013 (to J. M. A.) and BFU2010-15703 (to J. M. V.) and contracts Juan de la Cierva (to A. J. M.-G. and M. A. O.), a contract from the Consejo Superior de Investigaciones Científicas Junta de Ampliación de Estudios-Doctores (to A. J. M.-G.), a Formacion de Personal Universitario fellowship (to L. S.), and a fellowship from the Madrid Regional Government (to M. S.) ; Peer reviewed

Nonsense-mediated mRNA decay (NMD) is a surveillance pathway that degrades aberrant mRNAs and also regulates the expression of a wide range of physiological transcripts. RUVBL1 and RUVBL2 AAA-ATPases form an hetero-hexameric ring that is part of several macromolecular complexes such as INO80, SWR1, and R2TP. Interestingly, RUVBL1-RUVBL2 ATPase activity is required for NMD activation by an unknown mechanism. Here, we show that DHX34, an RNA helicase regulating NMD initiation, directly interacts with RUVBL1-RUVBL2 in vitro and in cells. Cryo-EM reveals that DHX34 induces extensive changes in the N-termini of every RUVBL2 subunit in the complex, stabilizing a conformation that does not bind nucleotide and thereby down-regulates ATP hydrolysis of the complex. Using ATPase-deficient mutants, we find that DHX34 acts exclusively on the RUVBL2 subunits. We propose a model, where DHX34 acts to couple RUVBL1-RUVBL2 ATPase activity to the assembly of factors required to initiate the NMD response. ; Spanish Ministry of Science and Innovation SAF2017-82632-P Andres Lopez-Perrote Carlos F Rodriguez Marina Serna Oscar Llorca. Autonomous Government of Madrid Y2018/BIO4747 Ana Gonzalez-Corpas Oscar Llorca. Autonomous Government of Madrid P2018/NMT4443 Ana Gonzalez-Corpas Oscar Llorca MRC Core funding Javier F Caceres Spanish Ministry of Science and Innovation BES-2015-071348 Carlos F Rodriguez The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication. ; Sí