Divergent architecture of the heterotrimeric NatC complex explains N-terminal acetylation of cognate substrates

The heterotrimeric NatC complex, comprising the catalytic Naa30 and the two auxiliary subunits Naa35 and Naa38, co-translationally acetylates the N-termini of numerous eukaryotic target proteins. Despite its unique subunit composition, its essential role for many aspects of cellular function and its suggested involvement in disease, structure and mechanism of NatC have remained unknown. Here, we present the crystal structure of the Saccharomyces cerevisiae NatC complex, which exhibits a strikingly different architecture compared to previously described N-terminal acetyltransferase (NAT) complexes. Cofactor and ligand-bound structures reveal how the first four amino acids of cognate substrates are recognized at the Naa30–Naa35 interface. A sequence-specific, ligand-induced conformational change in Naa30 enables efficient acetylation. Based on detailed structure–function studies, we suggest a catalytic mechanism and identify a ribosome-binding patch in an elongated tip region of NatC. Our study reveals how NAT machineries have divergently evolved to N-terminally acetylate specific subsets of target proteins

pH‐dependent protonation of surface carboxylate groups in PsbO enables local buffering and triggers structural changes

Photosystem II (PSII) catalyzes the splitting of water, releasing protons and dioxygen. Its highly conserved subunit PsbO extends from the oxygen‐evolving center (OEC) into the thylakoid lumen and stabilizes the catalytic Mn4CaO5 cluster. The high degree of conservation of accessible negatively charged surface residues in PsbO suggests additional functions, as local pH buffer or by affecting the flow of protons. For this discussion, we provide an experimental basis, through the determination of pKa values of water‐accessible aspartate and glutamate side‐chain carboxylate groups by means of NMR. Their distribution is strikingly uneven, with high pKa values around 4.9 clustered on the luminal PsbO side and values below 3.5 on the side facing PSII. pH‐dependent changes in backbone chemical shifts in the area of the lumen‐exposed loops are observed, indicating conformational changes. In conclusion, we present a site‐specific analysis of carboxylate group proton affinities in PsbO, providing a basis for further understanding of proton transport in photosynthesis

The "Abnormal" State : Identity, Norm/Exception and Japan

The term ‘abnormal’ has frequently been used to describe post-war Japan. Together with the idea that the country will, or should have to, ‘normalise’ its foreign and security policy, it has been reproduced in both academia and Japanese society. Why is Japan branded as ‘abnormal’, and from where does the desire to ‘normalise’ it come? Drawing on a relational concept of identity, and the distinction between norm and exception, this article argues that the ‘abnormality–normalisation nexus’ can be understood in terms of three identity-producing processes: (1) the process whereby the Japanese Self is socialised in US/‘Western’ norms, ultimately constructing it as an Other in the international system; (2) the process whereby the Japanese Self imagines itself as ‘legitimately exceptional’ (what is called ‘exceptionalisation’), but also ‘illegitimately abnormal’ — both of which are epitomised by Japan’s ‘pacifism’; and (3) the process whereby both the Self’s ‘negative abnormality’ and China/Asia are securitised in attempts to realise a more ‘normal’ (or super-normal) Japanese Self. How Japan is inter subjectively constructed on a scale between ‘normal’ and ‘abnormal’ enables and constrains action. Although Japan has not remilitarised nearly as much in the 2000s as is often claimed, these processes might very well forebode an exceptional decision to become ‘normal’ and therefore more significant steps towards remilitarisation