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Abstract The photolysis of disulfide bonds is implicated in denaturation of proteins exposed to ultraviolet light. Despite this biological relevance in stabilizing the structure of many proteins, the mechanisms of disulfide photolysis are still contested after decades of research. Herein, we report new insight into the photochemistry of L-cystine in aqueous solution by femtosecond X-ray absorption spectroscopy at the sulfur K-edge. We observe homolytic bond cleavage upon ultraviolet irradiation and the formation of thiyl radicals as the single primary photoproduct. Ultrafast thiyl decay due to geminate recombination proceeds at a quantum yield of >80 % within 20 ps. These dynamics coincide with the emergence of a secondary product, attributed to the generation of perthiyl radicals. From these findings, we suggest a mechanism of perthiyl radical generation from a vibrationally excited parent molecule that asymmetrically fragments along a carbon-sulfur bond. Our results point toward a dynamic photostability of the disulfide bridge in condensed-phase.

Abstract The structures, strain fields, and defect distributions in solid materials underlie the mechanical and physical properties across numerous applications. Many modern microstructural microscopy tools characterize crystal grains, domains and defects required to map lattice distortions or deformation, but are limited to studies of the (near) surface. Generally speaking, such tools cannot probe the structural dynamics in a way that is representative of bulk behavior. Synchrotron X-ray diffraction based imaging has long mapped the deeply embedded structural elements, and with enhanced resolution, dark field X-ray microscopy (DFXM) can now map those features with the requisite nm-resolution. However, these techniques still suffer from the required integration times due to limitations from the source and optics. This work extends DFXM to X-ray free electron lasers, showing how the $$10^{12}$$ 10 12 photons per pulse available at these sources offer structural characterization down to 100 fs resolution (orders of magnitude faster than current synchrotron images). We introduce the XFEL DFXM setup with simultaneous bright field microscopy to probe density changes within the same volume. This work presents a comprehensive guide to the multi-modal ultrafast high-resolution X-ray microscope that we constructed and tested at two XFELs, and shows initial data demonstrating two timing strategies to study associated reversible or irreversible lattice dynamics.

The study of water at high pressure and temperature is essential for understanding planetary interiors but is hampered by the high reactivity of water at extreme conditions. Here, indirect X-ray laser heating of water in a diamond anvil cell is realized via a gold absorber, showing no evidence of reactivity.

Abstract In Korea, subtype B is the predominant variant of HIV-1, but full genome sequencing and analysis of its viral variants are lacking. We performed near full-length genome (NFLG) sequencing and phylogenetic and recombination analyses of fifty plasma samples from HIV-positive men who have sex with men (MSM) from a Korea HIV/AIDS cohort study. Viral genomes were amplified and the near-full-length sequences were determined using next-generation sequencing (NGS) and Sanger sequencing. We focused on the HIV-1 subtype classification and identification of HIV recombinants. Twelve HIV-1 NFLGs were determined: ten were subtyped as pure HIV-1 subtype B and two recombinant strains as a common subtype CRF07_BC, and a novel subtype CRF43_02G recombined with CRF02_AG again, or a new CRF02_AG and subtype G recombinant. For the ten NFLGs determined by NGS, “the novel recombinant emerged at approximately 2003 and the other nine subtype B about 2004 or 2005”. This is the first report analyzing HIV-1 NFLG, including recombinants and clinical characteristics, by subtype among MSM in Korea. Our results provide novel insights for understanding the recombinants in the HIV-1 epidemic in Korea.

Mutations in the MLL4 gene can cause Kabuki syndrome, whose underlying molecular mechanisms are unclear. Here, the authors show that Mll4 epigenetically regulates the transcriptional program leading to the formation of GHRH-neurons in the developing mouse hypothalamus.

Despite the crucial physiological processes governed by neurons in the hypothalamic arcuate nucleus (ARC), the developmental pathways and regulators for ARC neurons remain understudied. In this study the authors use single cell RNA-seq analyses of mouse embryonic ARC to identify cell type-specific markers for developing ARC neurons and give key insight into the underlying developmental pathways and regulators.

Laser-matter interaction has been intensively studied in equilibrium states, but irreversible processes in a highly nonequilibrium state at nanoscales remains elusive due to experimental challenges. Here, Ihm et al. image heterogeneous melting of gold nanoparticles with nanometer and picosecond resolution.

In the hypothalamus, the arcuate nucleus (ARC) contains AgRP-neurons that regulate energy balance as well as GHRH-neurons that regulate linear growth. Here, the authors looked at how the transcription factors Dlx1/2 and Otp link development of AgRP- and GHRH-neurons.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The utility of a universal reference sequence for human genome comparisons is dependent on the ethnic origins of the individuals being sequenced. Here the authors report a Korean reference genome and consensus variome, and show that an ethnically-relevant reference can improve variant detection.

Nature Communications 7: Article number: 13637 (2016): Published 24 November 2016; Updated 9 October 2017. The original version of this Article contained an error in the email address of the corresponding author George Church. The correct email is gchurch@genetics.med.harvard.edu. The error has beencorrected in the HTML and PDF versions of the Article.