First European Polar Science Week

During the high-level opening session, John Bell, European Commission Director, Directorate General Research & Innovation, European Commission, and Josef Aschbacher, ESA Director praised the cooperation between the EC and ESA, in the context of the Earth System Science Arrangement. They confirmed their willingness to advance towards a better coordination and integration of EC and ESA activities in Polar research. The European Union has been funding a significant number of Polar projects as part of the Framework programmes for Research and Innovation. In 2015, the funding of the EU-PolarNet project was instrumental as it enables stakeholders to coordinate activities across Europe. EU-PolarNet has delivered a number of key outputs among which the Integrated European Research Programme (EPRP). This report is the result of a process involving many players identifying key research and knowledge gaps, feeding into European Commission’s policy making. The launch of the new EU-PolarNet 2 project during the conference showed the willingness of the EU to sustain these coordination efforts. EU-PolarNet 2 will play a key role to reinforce the science to policy interface and to increase coordination of polar research activities at European level, with a better understanding of what is done at national level. EU-PolarNet 2 will also lead the coordination of the EU Polar Cluster in close cooperation with the ESA Polaractivities. The EU Polar Cluster, launched in 2016, has been extending in terms of number of projects (21 projects and 2 initiatives) and it confirmed its objective to reinforce cooperation across projects on a number of areas of common interest. Transnational cooperation of all involved actors (researchers and stakeholders) and European-wide coordination of Polar research efforts are decisively important, particularly in tackling major societal challenges such as climate change. Scientific knowledge has to be appropriately disseminated to inform policymakers with a high level of expertise and to support evidence-based policy making. The projects from the ESA Polar Cluster confirmed the need to work closer with the EU funded projects. This is fully supported by ESA, which launched a call for tender to facilitate innovative scientific developments through collaborative research and networking opportunities in the Polar research domain and in particular between the ESA and EU Polar Clusters.

Genetic Code Evolution Reconstructed with Aligned Metrics

Sequence homology in pre-divergence tRNA species revealed cofactor/adaptors cognate for 16 amino acids derived from oxaloacetate, pyruvate, phosphoglycerate, or phosphoenolpyruvate were related. Synthesis path-distances of these amino acids correlated with phylogenetic depth, reflecting relative residue frequency in pre-divergence sequences. Both metrics were thus aligned in the four sub-families of the Aspartate family, and misaligned in the small Glutamate family; a functional difference was noted and seen to parallel synthetase duality. Amino acid synthetic order, based on path-distances, indicate NH4+ fixer amino acids, Asp1, Asn2, and homologues, Glu1, Gln2, formed the first code. Together with a termination signal, they acquired all four triplet 4-sets in the XAN column (X, 5’ coding site; N, any 3’-base). An invariant mid-A conformed with pre-code translation on a poly(A) template by a ratchet-equipped ribosome resulting in random, polyanionic polypeptides. Code expansion occurred in a compact (mutation minimizing) columnwise pattern, (XAN) ➔ XCN ➔ XGN ➔ XUN; with increasing mean path-distance, (1.5) ➔ 4 ➔ 5 ➔ 7 steps; amino acid side-chain hydrophobicity, (+6.6) ➔ −0.8 ➔ −1.5 ➔ −3.2 kcal/ mol; codon:anticodon H bond enthalpy (selection for bond-strength), (−12.5) ➔ −17.5 ➔ −15.5 ➔ −14.5 kcal/ mol; and precursorspecific 5’-base, A, oxaloacetate, G, pyruvate/oxaloacetate, U, phosphoglycerate/oxaloacetate, C, oxoglutarate, forming horizontal code domains. Codon bias evidence corroborated the XCN ➔ XGN step in expansion, and revealed row GNN coevolved with ANN, on correction for overprinting. Extended surfaceattachment (Fajan-Paneth principle) by pro-Fd[5] and bilayer partitioning by H+ ATPase proteolipid-h1 subunit implicated expansion phase proteins in driving increases in side-chain hydrophobicity during code expansion. 3’-Base recruitment in pre-assigned codon boxes added six long (9-to 14-step) path amino acid, bearing a basic, or cyclic, side-chain; 3 of 4 polar, post-expansion amino acids acquired polar cluster NAN codons and 2 of 3 non-polar (Ile7 included) acquired non-polar cluster NUN codons, yieldng a split-box pair homology of p = 5.4×10-3. All eight overprinted codon boxes (GAYR for Asp1, Glu1 included) exhibit weak codon:anticodon H-bond enthalpy, −14 kcal/mol or higher, in three of six distinct code enthalpy states.

Ultrahigh energy storage and electrocaloric performance achieved in SrTiO3 amorphous thin films via polar cluster engineering

High energy storage density and a reversible electrocaloric effect are simultaneously achieved in Sr0.995(Na0.5Bi0.5)0.005(Ti0.99Mn0.01)O3 amorphous thin films via polar cluster engineering.

Tuning the self-organization of confined active particles by the steepness of the trap

A 2D polar layer of self-propelling and self-aligning particles, rotating along the boundary of a circular trap, becomes a round-shaped polar cluster with hexagonal order when the steepness of the trap-boundary is reduced gradually.

Substrate-triggered position switching of TatA and TatB during Tat transport in Escherichia coli

The twin-arginine protein transport (Tat) machinery mediates the translocation of folded proteins across the cytoplasmic membrane of prokaryotes and the thylakoid membrane of plant chloroplasts. The Escherichia coli Tat system comprises TatC and two additional sequence-related proteins, TatA and TatB. The active translocase is assembled on demand, with substrate-binding at a TatABC receptor complex triggering recruitment and assembly of multiple additional copies of TatA; however, the molecular interactions mediating translocase assembly are poorly understood. A ‘polar cluster’ site on TatC transmembrane (TM) helix 5 was previously identified as binding to TatB. Here, we use disulfide cross-linking and molecular modelling to identify a new binding site on TatC TM helix 6, adjacent to the polar cluster site. We demonstrate that TatA and TatB each have the capacity to bind at both TatC sites, however in vivo this is regulated according to the activation state of the complex. In the resting-state system, TatB binds the polar cluster site, with TatA occupying the TM helix 6 site. However when the system is activated by overproduction of a substrate, TatA and TatB switch binding sites. We propose that this substrate-triggered positional exchange is a key step in the assembly of an active Tat translocase.

Assembling the Tat protein translocase

The twin-arginine protein translocation system (Tat) transports folded proteins across the bacterial cytoplasmic membrane and the thylakoid membranes of plant chloroplasts. The Tat transporter is assembled from multiple copies of the membrane proteins TatA, TatB, and TatC. We combine sequence co-evolution analysis, molecular simulations, and experimentation to define the interactions between the Tat proteins of Escherichia coli at molecular-level resolution. In the TatBC receptor complex the transmembrane helix of each TatB molecule is sandwiched between two TatC molecules, with one of the inter-subunit interfaces incorporating a functionally important cluster of interacting polar residues. Unexpectedly, we find that TatA also associates with TatC at the polar cluster site. Our data provide a structural model for assembly of the active Tat translocase in which substrate binding triggers replacement of TatB by TatA at the polar cluster site. Our work demonstrates the power of co-evolution analysis to predict protein interfaces in multi-subunit complexes.