Self-assembly Controls Self-cleavage of HHR from ASBVd (−): a Combined SANS and Modeling Study

International audienceIn the Avocado Sunblotch Viroid (ASBVd: 249-nt) from the Avsunviroidae family, a symmetric rolling-circle replication operates through an autocatalytic mechanism mediated by hammerhead ribozymes (HHR) embedded in both polarity strands. The concatenated multimeric ASBVd (+) and ASBVd (−) RNAs thus generated are processed by cleavage to unit-length where ASBVd (−) self-cleaves with more efficiency. Absolute scale small angle neutron scattering (SANS) revealed a temperature-dependent dimer association in both ASBVd (−) and its derived 79-nt HHR (−). A joint thermodynamic analysis of SANS and catalytic data indicates the rate-determining step corresponds to the dimer/monomer transition. 2D and 3D models of monomeric and dimeric HHR (−) suggest that the inter-molecular contacts stabilizing the dimer (between HI and HII domains) compete with the intra-molecular ones stabilizing the active conformation of the full-length HHR required for an efficient self-cleavage. Similar competing intra- and inter-molecular contacts are proposed in ASBVd (−) though with a remoter region from an extension of the HI domain

A central cavity within the holo-translocon suggests a mechanism for membrane protein insertion.

The conserved SecYEG protein-conducting channel and the accessory proteins SecDF-YajC and YidC constitute the bacterial holo-translocon (HTL), capable of protein-secretion and membrane-protein insertion. By employing an integrative approach combining small-angle neutron scattering (SANS), low-resolution electron microscopy and biophysical analyses we determined the arrangement of the proteins and lipids within the super-complex. The results guided the placement of X-ray structures of individual HTL components and allowed the proposal of a model of the functional translocon. Their arrangement around a central lipid-containing pool conveys an unexpected, but compelling mechanism for membrane-protein insertion. The periplasmic domains of YidC and SecD are poised at the protein-channel exit-site of SecY, presumably to aid the emergence of translocating polypeptides. The SecY lateral gate for membrane-insertion is adjacent to the membrane 'insertase' YidC. Absolute-scale SANS employing a novel contrast-match-point analysis revealed a dynamic complex adopting open and compact configurations around an adaptable central lipid-filled chamber, wherein polytopic membrane-proteins could fold, sheltered from aggregation and proteolysis

H2O : première molécule de la Vie

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Salt Survivors

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Ecology of Protein Dynamics

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Fleur de sel

Mélanie and her husband, a scientist specialising in the biology of salt lakes, go on holiday to theCamargue to observe pink flamingos and visit the saltworks.Mélanie et son époux, scientifique spécialisé dans la biologie de milieux hypersalins, partent en vacancesen Camargue pour observer les flamants roses et visiter les salins

Hydration shells with a pinch of salt.

International audienceThe discovery of extreme halophile microorganisms in the Dead Sea, which are specifically dependent on a multimolar salt environment to survive, stimulated major developments in biology and physical chemistry. The minireview focuses on the molecular level. After a brief introduction to the history of halophile studies, protein and nucleic acid solvent interactions and their influence on macromolecular structure stabilization and dynamics are discussed