Structural biology: Lipid gymnastics

Nature 524, 7566 (2015). doi:10.1038/nature15202

Authors: Alice Verchère & Anant K. Menon

Crystal structures of the bacterial protein PglK uncover structural features that suggest how the protein 'flips' lipid-bound oligosaccharide molecules from one side of the cell membrane to the other. See Article p.433

Structure and mechanism of an active lipid-linked oligosaccharide flippase

Nature 524, 7566 (2015). doi:10.1038/nature14953

Authors: Camilo Perez, Sabina Gerber, Jérémy Boilevin, Monika Bucher, Tamis Darbre, Markus Aebi, Jean-Louis Reymond & Kaspar P. Locher

The flipping of membrane-embedded lipids containing large, polar head groups is slow and energetically unfavourable, and is therefore catalysed by flippases, the mechanisms of which are unknown. A prominent example of a flipping reaction is the translocation of lipid-linked oligosaccharides that serve as donors in

SEC14L2 enables pan-genotype HCV replication in cell culture

Nature 524, 7566 (2015). doi:10.1038/nature14899

Authors: Mohsan Saeed, Ursula Andreo, Hyo-Young Chung, Christine Espiritu, Andrea D. Branch, Jose M. Silva & Charles M. Rice

Since its discovery in 1989, efforts to grow clinical isolates of the hepatitis C virus (HCV) in cell culture have met with limited success. Only the JFH-1 isolate has the capacity to replicate efficiently in cultured hepatoma cells without cell culture-adaptive mutations. We hypothesized that cultured cells lack one or more factors required for the replication of clinical isolates. To identify the missing factors, we transduced Huh-7.5 human hepatoma cells with a pooled lentivirus-based human complementary DNA (cDNA) library, transfected the cells with HCV subgenomic replicons lacking adaptive mutations, and selected for stable replicon colonies. This led to the identification of a single cDNA, SEC14L2, that enabled RNA replication of diverse HCV genotypes in several hepatoma cell lines. This effect was dose-dependent, and required the continuous presence of SEC14L2. Full-length HCV genomes also replicated and produced low levels of infectious virus. Remarkably, SEC14L2-expressing Huh-7.5 cells also supported HCV replication following inoculation with patient sera. Mechanistic studies suggest that SEC14L2 promotes HCV infection by enhancing vitamin E-mediated protection against lipid peroxidation. This provides a foundation for development of in vitro replication systems for all HCV isolates, creating a useful platform to dissect the mechanisms by which cell culture-adaptive mutations act.