Semiclassical transmission across transition states

It is shown that the probability of quantum-mechanical transmission across a phase space bottleneck can be compactly approximated using an operator derived from a complex Poincar\'e return map. This result uniformly incorporates tunnelling effects with classically-allowed transmission and generalises a result previously derived for a classically small region of phase space.Comment: To appear in Nonlinearit

Structural basis of nucleotide sugar transport across the Golgi membrane

Glycosylation is a fundamental cellular process that, in eukaryotes, occurs in the lumen of both the Golgi apparatus and the endoplasmic reticulum1. Nucleotide sugar transporters (NSTs) are an essential component of the glycosylation pathway, providing the diverse range of substrates required for the glycosyltransferases2,3. NSTs are linked to several developmental and immune disorders in humans, and in pathogenic microbes they have an important role in virulence4,5,6,7,8. How NSTs recognize and transport activated monosaccharides, however, is currently unclear. Here we present the crystal structure of an NST, the GDP–mannose transporter Vrg4, in both the substrate-free and the bound states. A hitherto unobserved requirement of short-chain lipids in activating the transporter supports a model for regulation within the highly dynamic membranes of the Golgi apparatus. Our results provide a structural basis for understanding nucleotide sugar recognition, and provide insights into the transport and regulatory mechanism of this family of intracellular transporters