Autophagy and polyglutamine diseases

AbstractIn polyglutamine diseases, an abnormally elongated polyglutamine tract results in protein misfolding and accumulation of intracellular aggregates. The length of the polyglutamine expansion correlates with the tendency of the mutant protein to aggregate, as well as with neuronal toxicity and earlier disease onset. Although currently there is no effective cure to prevent or slow down the progression of these neurodegenerative disorders, increasing the clearance of mutant proteins has been proposed as a potential therapeutic approach. The ubiquitin–proteasome system and autophagy are the two main degradative pathways responsible for eliminating misfolded and unnecessary proteins in the cell. We will review some of the studies that have proposed autophagy as a strategy to reduce the accumulation of polyglutamine-expanded protein aggregates and protect against mutant protein neurotoxicity. We will also discuss some of the currently known mechanisms that induce autophagy, which may be beneficial for the treatment of these and other neurodegenerative disorders

Feasibility of Imaging Myelin Lesions in Multiple Sclerosis

The goal of this study was to provide a feasibility assessment for PET imaging of multiple sclerosis (MS) lesions based on their decreased myelin content relative to the surrounding normal-appearing brain tissue. The imaging agent evaluated for this purpose is a molecule that binds strongly and specifically to myelin basic protein. Physiology-based pharmacokinetic modeling combined with PET image simulation applied to a brain model was used to examine whether such an agent would allow the differentiation of artificial lesions 4–10 mm in diameter from the surrounding normal-looking white and gray matter. Furthermore, we examined how changes in agent properties, model parameters, and experimental conditions can influence imageability, identifying a set of conditions under which imaging of MS lesions might be feasible. Based on our results, we concluded that PET imaging has the potential to become a useful complementary method to MRI for MS diagnosis and therapy monitoring

Dielectronic Recombination in Li+ Ions

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Fluorescence-Based Phenotypic Selection Allows Forward Genetic Screens in Haploid Human Cells

The isolation of haploid cell lines has recently allowed the power of forward genetic screens to be applied to mammalian cells. The interest in applying this powerful genetic approach to a mammalian system is only tempered by the limited utility of these screens, if confined to lethal phenotypes. Here we expand the scope of these approaches beyond live/dead screens and show that selection for a cell surface phenotype via fluorescence-activated cell sorting can identify the key molecules in an intracellular pathway, in this case MHC class I antigen presentation. Non-lethal haploid genetic screens are widely applicable to identify genes involved in essentially any cellular pathway

Monospecific inhibitors show that both mannan-binding lectin-associated serine protease (MASP)-1 and -2 are essential for lectin pathway activation and reveal structural plasticity of MASP-2.

The lectin pathway is an antibody-independent activation route of the complement system. It provides immediate defense against pathogens and altered self-cells, but it also causes severe tissue damage after stroke, heart attack and other ischemia reperfusion injuries. The pathway is triggered by target-binding of pattern recognition molecules leading to the activation of zymogen mannan-binding lectin-associated serine proteases (MASPs). MASP-2 is considered as the autonomous pathway- activator while MASP-1 as an auxiliary component. We evolved a pair of monospecific MASP inhibitors. In accordance with the key role of MASP-2, the MASP-2 inhibitor completely blocks the lectin pathway activation. Importantly, the MASP-1 inhibitor does the same demonstrating that MASP-1 is not an auxiliary but an essential pathway component. We report the first Michaelis- like complex structures of MASP-1 and MASP-2 formed with substrate-like inhibitors. The 1.28 A resolution MASP-2 structure reveals significant plasticity of the protease suggesting that either an induced fit or a conformational selection mechanism should contribute to the extreme specificity of the enzyme

Mutation in VPS35 associated with Parkinson's disease impairs WASH complex association and inhibits autophagy

Endosomal protein sorting controls the localization of many physiologically important proteins and is linked to several neurodegenerative diseases. VPS35 is a component of the retromer complex, which mediates endosome-to-Golgi retrieval of membrane proteins such as the cation-independent mannose 6-phosphate receptor. Furthermore, retromer is also required for the endosomal recruitment of the actin nucleation promoting WASH complex. The VPS35 D620N mutation causes a rare form of autosomal-dominant Parkinson’s disease (PD). Here we show that this mutant associates poorly with the WASH complex and impairs WASH recruitment to endosomes. Autophagy is impaired in cells expressing PD-mutant VPS35 or lacking WASH. The autophagy defects can be explained, at least in part, by abnormal trafficking of the autophagy protein ATG9A. Thus, the PD-causing D620N mutation in VPS35 restricts WASH complex recruitment to endosomes, and reveals a novel role for the WASH complex in autophagosome formation

Glutamate 270 plays an essential role in K activation and domain closure of Thermus thermophilus isopropylmalate dehydrogenase

The mutant E270A of Thermus thermophilus 3-isopropylmalate dehydrogenase exhibits largely reduced (∼1%) catalytic activity and negligible activation by K+ compared to the wild-type enzyme. A 3–4 kcal/mol increase in the activation energy of the catalysed reaction upon this mutation could also be predicted by QM/MM calculations. In the X-ray structure of the E270A mutant a water molecule was observed to take the place of K+. SAXS and FRET experiments revealed the essential role of E270 in stabilisation of the active domain-closed conformation of the enzyme. In addition, E270 seems to position K+ into close proximity of the nicotinamide ring of NAD+ and the electron-withdrawing effect of K+ may help to polarise the aromatic ring in order to aid the hydride-transfer