Functional waters in intraprotein proton transfer monitored by FTIR difference spectroscopy

Much progress has been made in our understanding of water molecule reactions on surfaces, proton solvation in gas-phase water clusters and proton transfer through liquids. Compared with our advanced understanding of these physico-chemical systems, much less is known about individual water molecules and their cooperative behaviour in heterogeneous proteins during enzymatic reactions. Here we use time-resolved Fourier transform infrared spectroscopy (trFTIR) and in situ H2(18)O/H2(16)O exchange FTIR to determine how the membrane protein bacteriorhodopsin uses the interplay among strongly hydrogen-bonded water molecules, a water molecule with a dangling hydroxyl group and a protonated water cluster to transfer protons. The precise arrangement of water molecules in the protein matrix results in a controlled Grotthuss proton transfer, in contrast to the random proton migration that occurs in liquid water. Our findings support the emerging paradigm that intraprotein water molecules are as essential for biological functions as amino acids.     

Decoherence of matter waves by thermal emission of radiation

Emergent quantum technologies have led to increasing interest in decoherence--the processes that limit the appearance of quantum effects and turn them into classical phenomena. One important cause of decoherence is the interaction of a quantum system with its environment, which 'entangles' the two and distributes the quantum coherence over so many degrees of freedom as to render it unobservable. Decoherence theory has been complemented by experiments using matter waves coupled to external photons or molecules, and by investigations using coherent photon states, trapped ions and electron interferometers. Large molecules are particularly suitable for the investigation of the quantum-classical transition because they can store much energy in numerous internal degrees of freedom; the internal energy can be converted into thermal radiation and thus induce decoherence. Here we report matter wave interferometer experiments in which C70 molecules lose their quantum behaviour by thermal emission of radiation. We find good quantitative agreement between our experimental observations and microscopic decoherence theory. Decoherence by emission of thermal radiation is a general mechanism that should be relevant to all macroscopic bodies.     

Multi-colour organic light-emitting displays by solution processing

Organic light-emitting diodes (OLEDs) show promise for applications as high-quality self-emissive displays for portable devices such as cellular phones and personal organizers. Although monochrome operation is sufficient for some applications, the extension to multi-colour devices--such as RGB (red, green, blue) matrix displays--could greatly enhance their technological impact. Multi-colour OLEDs have been successfully fabricated by vacuum deposition of small electroluminescent molecules, but solution processing of larger molecules (electroluminescent polymers) would result in a cheaper and simpler manufacturing process. However, it has proved difficult to combine the solution processing approach with the high-resolution patterning techniques required to produce a pixelated display. Recent attempts have focused on the modification of standard printing techniques, such as screen printing and ink jetting, but those still have technical drawbacks. Here we report a class of electroluminescent polymers that can be patterned in a way similar to standard photoresist materials--soluble polymers with oxetane sidegroups that can be crosslinked photochemically to produce insoluble polymer networks in desired areas. The resolution of the process is sufficient to fabricate pixelated matrix displays. Consecutive deposition of polymers that are luminescent in each of the three RGB colours yielded a device with efficiencies comparable to state-of-the-art OLEDs and even slightly reduced onset voltages.     

Hepatocyte nuclear factor 4alpha controls the development of a hepatic epithelium and liver morphogenesis

Although advances have been made in understanding cell differentiation, only rudimentary knowledge exists concerning how differentiated cells form tissues and organs. We studied liver organogenesis because the cell and tissue architecture of this organ is well defined. Approximately 60% of the adult liver consists of hepatocytes that are arranged as single-cell anastomosing plates extending from the portal region of the liver lobule toward the central vein. The basal surface of the hepatocytes is separated from adjacent sinusoidal endothelial cells by the space of Disse, where the exchange of substances between serum and hepatocytes takes place. The hepatocyte's apical surface forms bile canaliculi that transport bile to the hepatic ducts. Proper liver architecture is crucial for hepatic function and is commonly disrupted in disease states, including cirrhosis and hepatitis. Here we report that hepatocyte nuclear factor 4alpha (Hnf4alpha) is essential for morphological and functional differentiation of hepatocytes, accumulation of hepatic glycogen stores and generation of a hepatic epithelium. We show that Hnf4alpha is a dominant regulator of the epithelial phenotype because its ectopic expression in fibroblasts induces a mesenchymal-to-epithelial transition. Most importantly, the morphogenetic parameters controlled by Hnf4alpha in hepatocytes are essential for normal liver architecture, including the organization of the sinusoidal endothelium.     

Membrane biology and signal transduction

Posters

Membrane biology and signal transduction     

DMP1 mutations in autosomal recessive hypophosphatemia implicate a bone matrix protein in the regulation of phosphate homeostasis

Hypophosphatemia is a genetically heterogeneous disease. Here, we mapped an autosomal recessive form (designated ARHP) to chromosome 4q21 and identified homozygous mutations in DMP1 (dentin matrix protein 1), which encodes a non-collagenous bone matrix protein expressed in osteoblasts and osteocytes. Intact plasma levels of the phosphaturic protein FGF23 were clearly elevated in two of four affected individuals, providing a possible explanation for the phosphaturia and inappropriately normal 1,25(OH)2D levels and suggesting that DMP1 may regulate FGF23 expression.     

Mutations in the gene encoding the 3'-5' DNA exonuclease TREX1 are associated with systemic lupus erythematosus

TREX1 acts in concert with the SET complex in granzyme A-mediated apoptosis, and mutations in TREX1 cause Aicardi-Goutières syndrome and familial chilblain lupus. Here, we report monoallelic frameshift or missense mutations and one 3' UTR variant of TREX1 present in 9/417 individuals with systemic lupus erythematosus but absent in 1,712 controls (P = 4.1 x 10(-7)). We demonstrate that two mutant TREX1 alleles alter subcellular targeting. Our findings implicate TREX1 in the pathogenesis of SLE.     

Loss of cyclophilin D reveals a critical role for mitochondrial permeability transition in cell death

Mitochondria play a critical role in mediating both apoptotic and necrotic cell death. The mitochondrial permeability transition (mPT) leads to mitochondrial swelling, outer membrane rupture and the release of apoptotic mediators. The mPT pore is thought to consist of the adenine nucleotide translocator, a voltage-dependent anion channel, and cyclophilin D (the Ppif gene product), a prolyl isomerase located within the mitochondrial matrix. Here we generated mice lacking Ppif and mice overexpressing cyclophilin D in the heart. Ppif null mice are protected from ischaemia/reperfusion-induced cell death in vivo, whereas cyclophilin D-overexpressing mice show mitochondrial swelling and spontaneous cell death. Mitochondria isolated from the livers, hearts and brains of Ppif null mice are resistant to mitochondrial swelling and permeability transition in vitro. Moreover, primary hepatocytes and fibroblasts isolated from Ppif null mice are largely protected from Ca2+-overload and oxidative stress-induced cell death. However, Bcl-2 family member-induced cell death does not depend on cyclophilin D, and Ppif null fibroblasts are not protected from staurosporine or tumour-necrosis factor-alpha-induced death. Thus, cyclophilin D and the mitochondrial permeability transition are required for mediating Ca2+- and oxidative damage-induced cell death, but not Bcl-2 family member-regulated death.