Read about some of the latest publications to come from the Department.
C-terminal propeptide is required for fibrillin-1 secretion and blocks premature assembly through linkage to domains cbEGF41-43. Jensen, SA, Aspinall, G and Handford, PA. PNAS (2014) published ahead of print June 30 doi:10.1073/pnas.1401697111
Fibrillin microfibrils are extracellular matrix assemblies that provide the connective tissues of metazoan species with many of their biomechanical properties. They are also involved in regulating the production of extracellular matrix through their interactions with growth factors such as transforming growth factor-β. The process of microfibril assembly and its regulation are poorly understood. Jensen et al have investigated the role of the conserved C-terminal propeptide of fibrillin-1 using an in vitro microfibril assay in which HEK293T cells, transiently expressing a GFP-tagged variant of fibrillin-1, are co-cultured with fibroblasts to produce a recombinant microfibril network. Their data show that the C-terminal propeptide plays a crucial role in preventing premature intracellular microfibril assembly.
Uukuniemi phlebovirus assembly and secretion leaves a functional imprint on the virion glycome. Crispin, M, Harvey, DJ, Bitto, D, Halldorsson, S, Bonomelli, C, Edgeworth, M, Scrivens, JH, Huiskonen, JT and Bowden, TA. J Virology (2014) published ahead of print June 18 doi: 10.1128/JVI.01662-14
Uukuniemi virus (UUKV) is a model system for investigating the Phlebovirus genus of the Bunyaviridae. Crispin et al report the UUKV glycome, revealing differential processing of the Gn and Gc virion glycoproteins. Both glycoproteins display poly-N-acetyllactosamines, consistent with virion assembly in the medial Golgi apparatus, whereas oligomannose-type glycans required for DC-SIGN-dependent cellular attachment are predominant on Gc. Local virion structure and the route of viral egress from the cell leaves a functional imprint on the phleboviral glycome.
A hydrophobic barrier deep within the inner pore of the TWIK-1 K2P potassium channel. Aryal, P, Abd-Wahab, F, Bucci, G, Sansom, MSP and Tucker, SJ. Nature Communications 5 (2014) doi:10.1038/ncomms5377
Recent X-ray crystal structures of the two-pore domain (K2P) family of potassium channels have revealed a unique structural architecture at the point where the cytoplasmic bundle-crossing gate is found in most other tetrameric K+ channels. However, despite the apparently open nature of the inner pore in the TWIK-1 (K2P1/KCNK1) crystal structure, the reasons underlying its low levels of functional activity remain unclear. In this study, Aryal et al use a combination of molecular dynamics simulations and functional validation to demonstrate that TWIK-1 possesses a hydrophobic barrier deep within the inner pore, and that stochastic dewetting of this hydrophobic constriction acts as a major barrier to ion conduction. These results not only provide an important insight into the mechanisms which control TWIK-1 channel activity, but also have important implications for our understanding of how ion permeation may be controlled in similar ion channels and pores.
Stoichiometry and turnover of the bacterial flagellar switch protein FliN. Delalez, NJ, Berry, RM and Armitage, JP. 1 July 2014 mBio vol. 5 no. 4 e01216-14
The flagellum is one of the most complex structures in a bacterial cell, with the core motor proteins conserved across species. Evidence is now emerging that turnover of some of these motor proteins depends on motor activity, suggesting that turnover is important for function. The switch complex transmits the chemosensory signal to the rotor. Delalez et al show, by using single-cell measurement, that both the copy number and the fraction of exchanging molecules vary with the rotational bias of the rotor. When the motor is locked in counterclockwise rotation, the copy number is similar to that determined by averaged, fixed methodologies, but when locked in a clockwise direction, the number is much lower, suggesting that that the switch complex ring is incomplete. Their results suggest that motor remodeling is an important component in tuning responses and adaptation at the motor.
A Plasmodium falciparum PHIST protein binds the virulence factor PfEMP1 and comigrates to knobs on the host cell surface. Oberli, A, Slater, LM, Cutts, E, Brand, F, Mundwiler-Pachlatko, E, Rusch, S, Masik, MFG, Erat, MC, Beck, HP and Vakonakis, I. Faseb J (2014) doi: 10.1096/fj.14-256057
Uniquely among malaria parasites, Plasmodium falciparum-infected erythrocytes (iRBCs) develop membrane protrusions, known as knobs, where the parasite adhesion receptor P. falciparum erythrocyte membrane protein 1 (PfEMP1) clusters. Knob formation and the associated iRBC adherence to host endothelium are directly linked to the severity of malaria and are functional manifestations of protein export from the parasite to the iRBC. Members of a family of exported proteins featuring Plasmodium helical interspersed subtelomeric (PHIST) domains have been implicated in host-parasite protein interactions and are differentially regulated in severe disease and among parasite isolates. Oberli et al show that PHIST member PFE1605w preferentially binds the PfEMP1 intracellular segment, comigrates with PfEMP1 during export, and locates in knobs. They resolved the first crystallographic structure of a PHIST protein and derived a partial model of the PHIST-PfEMP1 interaction from nuclear magnetic resonance. They propose that PFE1605w reinforces the PfEMP1-cytoskeletal connection in knobs and discuss the possible role of PHIST proteins as interaction hubs in the parasite exportome.
Lysine acetylation controls local protein conformation by influencing proline isomerization. Howe, FS, Boubriak, I, Sale, MJ, Nair, A, Clynes, D, Grijzenhout, A, Murray, SC, Woloszczuk, R and Mellor, J. Mol Cell (2014) Sep 4. 55:5, 733-744
Gene transcription responds to stress and metabolic signals to optimize growth and survival. The histone H3 tail is intrinsically disordered yet extensively modified. H3 lysine4 trimethylation (K4me3) facilitates state changes but how levels are coordinated with the environment is unclear. Howe et al show that lysine14 acetylation influences cis-trans isomerization at the alanine15-proline16 peptide bond to control gene-specific lysine4 trimethylation. Lysine acetylation in proximity to proline residues may seed alternative conformations in disordered regions allowing interactions with different effector proteins.