资源环境科技发展态势分析平台

Over the past 18,000 years, the residence time and amount of soil carbon stored in the Ganges-Brahmaputra basin have been controlled by the intensity of Indian Summer Monsoon rainfall, with greater carbon destabilization during wetter, warmer conditions.

The structure of human diacylglycerol O-acyltransferase 1, a membrane protein that synthesizes triacylglycerides, is solved with cryo-electron microscopy, providing insight into its function and mechanism of enzymatic activity.

Diacylglycerol O-acyltransferase 1 (DGAT1) synthesizes triacylglycerides and is required for dietary fat absorption and fat storage in humans(1). DGAT1 belongs to the membrane-bound O-acyltransferase (MBOAT) superfamily, members of which are found in all kingdoms of life and are involved in the acylation of lipids and proteins(2,3). How human DGAT1 and other mammalian members of the MBOAT family recognize their substrates and catalyse their reactions is unknown. The absence of three-dimensional structures also hampers rational targeting of DGAT1 for therapeutic purposes. Here we present the cryo-electron microscopy structure of human DGAT1 in complex with an oleoyl-CoA substrate. Each DGAT1 protomer has nine transmembrane helices, eight of which form a conserved structural fold that we name the MBOAT fold. The MBOAT fold in DGAT1 forms a hollow chamber in the membrane that encloses highly conserved catalytic residues. The chamber has separate entrances for each of the two substrates, fatty acyl-CoA and diacylglycerol. DGAT1 can exist as either a homodimer or a homotetramer and the two forms have similar enzymatic activity. The N terminus of DGAT1 interacts with the neighbouring protomer and these interactions are required for enzymatic activity.

A quantum dot device designed to host four electrons is used to demonstrate Nagaoka ferromagnetism-a model of itinerant magnetism that has so far been limited to theoretical investigation.

Engineered, highly controllable quantum systems are promising simulators of emergent physics beyond the simulation capabilities of classical computers(1). An important problem in many-body physics is itinerant magnetism, which originates purely from long-range interactions of free electrons and whose existence in real systems has been debated for decades(2,3). Here we use a quantum simulator consisting of a four-electron-site square plaquette of quantum dots(4) to demonstrate Nagaoka ferromagnetism(5). This form of itinerant magnetism has been rigorously studied theoretically(6-9) but has remained unattainable in experiments. We load the plaquette with three electrons and demonstrate the predicted emergence of spontaneous ferromagnetic correlations through pairwise measurements of spin. We find that the ferromagnetic ground state is remarkably robust to engineered disorder in the on-site potentials and we can induce a transition to the low-spin state by changing the plaquette topology to an open chain. This demonstration of Nagaoka ferromagnetism highlights that quantum simulators can be used to study physical phenomena that have not yet been observed in any experimental system. The work also constitutes an important step towards large-scale quantum dot simulators of correlated electron systems.