␥-Secretase is a multi-component enzyme complex that performs an intramembranous cleavage, releasing amyloid-␤ (A␤) peptides from processing intermediates of the ␤-amyloid precursor protein. Because A␤ peptides are thought to be causative for Alzheimer's disease, inhibiting ␥-secretase represents a potential treatment for this neurodegenerative condition. Whereas inhibitors directed at the active center of ␥-secretase inhibit the cleavage of all its substrates, certain non-steroidal antiinflammatory drugs (NSAIDs) have been shown to selectively reduce the production of the more amyloidogenic A␤(1-42) peptide without inhibiting alternative cleavages. In contrast to the majority of previous studies, however, we demonstrate that in cell-free systems the mode of action of selected NSAIDs and their derivatives, depending on the concentrations used, can either be classified as modulatory or inhibitory. At modulatory concentrations, a selective and, with respect to the substrate, noncompetitive inhibition of A␤(1-42) production was observed. At inhibitory concentrations, on the other hand, biochemical readouts reminiscent of a nonselective ␥-secretase inhibition were obtained. When these compounds were analyzed for their ability to displace a radiolabeled, transition-state analog inhibitor from solubilized enzyme, noncompetitive antagonism was observed. The allosteric nature of radioligand displacement suggests that NSAID-like inhibitors change the conformation of the ␥-secretase enzyme complex by binding to a novel site, which is discrete from the binding site for transition-state analogs and therefore distinct from the catalytic center. Consequently, drug discovery efforts aimed at this site may identify novel allosteric inhibitors that could benefit from a wider window for inhibition of ␥ (42)-cleavage over alternative cleavages in the ␤-amyloid precursor protein and, more importantly, alternative substrates.According to the "amyloid cascade hypothesis" an enhanced production or decreased clearance of toxic amyloid-␤ (A␤) 1 peptides is thought to be the cause of Alzheimer's disease (AD) (1). A␤ peptides are processing products (2) of the type I transmembrane protein ␤-amyloid precursor protein (␤APP) (3), which has undergone sequential cleavages by ␤-and ␥-secretase enzymes. A common denominator (reviewed by Hardy (4)) for mutations causative of familial AD (FAD) has been revealed, being abnormalities in the metabolism of ␤APP that appear to lead to an elevation of the production of the A␤(1-42) peptide species. This C-terminally elongated A␤ peptide is more prone to aggregation than the shorter and more abundant A␤(1-40) species. Consequently, the prevention of A␤ production by inhibiting either of the proteases required for processing of ␤APP is currently viewed as a promising approach toward a therapy for AD. The membrane-bound aspartyl protease ␤-site ␤APP-cleaving enzyme 1 (5, 6) is the major ␤-secretase required for the generation of A␤ peptides. ␤-Site ␤APP-cleaving enzyme 1 has been shown to cleave within th...

Gamma-secretase is the enzyme activity releasing the amyloid-beta peptide from membrane-bound processing intermediates derived from the beta-amyloid precursor protein. Cellular release and subsequent aggregation of the amyloid-beta peptide is thought to be causative for the pathogenesis of Alzheimer's disease. Gamma-secretase performs an unusual intramembranous cleavage and has been closely linked to a macromolecular complex containing presenilins. To generate a molecular probe for gamma-secretase, we have developed a novel biotinylated affinity ligand which is based on a specific inhibitor containing a hydroxyethylene dipeptide isostere, known to serve as a transition state analogue for aspartic proteinases. Using this probe we confirmed the presence of the presenilin heterodimer and mature nicastrin in the active enzyme complex and, furthermore, that substrate binding site(s) and active center(s) are spatially separated. Affinity precipitations suggest that only a discrete fraction of cellular presenilin is present in the active gamma-secretase complex and that both gamma(40)- and gamma(42)-activities are mediated by the same molecular entity. This was also reflected by a co-distribution of both enzyme activities in subcellular fractions enriched for trans-Golgi network membranes.

Intramembranous cleavage of the ␤-amyloid precursor protein by ␥-secretase is the final processing event generating amyloid-␤ peptides, which are thought to be causative agents for Alzheimer's disease. Missense mutations in the presenilin genes co-segregate with early-onset Alzheimer's disease, and, recently, a close biochemical linkage between presenilins and the identity of ␥-secretase has been established. Here we describe for the first time that certain potent ␥-secretase inhibitors are able to interfere with the endoproteolytic processing of presenilin 1 (PS1). In addition, we identified a novel ␥-secretase inhibitor, {1S-benzyl-4R-[1-(5-cyclohexyl-2-oxo-2,3-dihydro-1H-benzo[e][1,4]diazepin-3(R,S)-ylcarbamoyl)-S-ethylcarbamoyl]-2R-hydroxy-5-phenyl-pentyl}-carbamic acid tertbutyl ester (CBAP), which not only physically interacts with PS1, but upon chronic treatment produces a "pharmacological knock-down" of PS1 fragments. This indicates that the observed accumulation of full-length PS1 is caused by a direct inhibition of its endoproteolysis. The subsequent use of CBAP as a biological tool to increase full-length PS1 levels in the absence of exogenous PS1 expression has provided evidence that wild-type PS1 endoproteolysis is not required either for PS1/␥-secretase complex assembly or trafficking. Furthermore, in cellbased systems CBAP does not completely recapitulate PS1 loss-of-function phenotypes. Even though the ␤-amyloid precursor protein cleavage and the S3 cleavage of the Notch receptor are inhibited by CBAP, an impairment of Trk receptor maturation was not observed.

The CRISPR–Cas9 RNA-guided endonuclease system allows precise and efficient modification of complex genomes and is continuously developed to enhance specificity, alter targeting and add new functional moieties. However, one area yet to be explored is the base chemistry of the associated RNA molecules. Here we show the design and optimisation of hybrid DNA–RNA CRISPR and tracr molecules based on structure-guided approaches. Through careful mapping of the ribose requirements of Cas9, we develop hybrid versions possessing minimal RNA residues, which are sufficient to direct specific nuclease activity in vitro and in vivo with reduced off-target activity. We identify critical regions within these molecules that require ribose nucleotides and show a direct correlation between binding affinity/stability and cellular activity. This is the first demonstration of a non-RNA-guided Cas9 endonuclease and first step towards eliminating the ribose dependency of Cas9 to develop a XNA-programmable endonuclease.

The ubiquitin proteasome system is widely postulated to be a new and important field of drug discovery for the future, with the ubiquitin specific proteases (USPs) representing one of the more attractive target classes within the area. Many USPs have been linked to critical axes for therapeutic intervention, and the finding that USP28 is required for c-Myc stability suggests that USP28 inhibition may represent a novel approach to targeting this so far undruggable oncogene. Here, we describe the discovery of the first reported inhibitors of USP28, which we demonstrate are able to bind to and inhibit USP28, and while displaying a dual activity against the closest homologue USP25, these inhibitors show a high degree of selectivity over other deubiquitinases (DUBs). The utility of these compounds as valuable probes to investigate and further explore cellular DUB biology is highlighted by the demonstration of target engagement against both USP25 and USP28 in cells. Furthermore, we demonstrate that these inhibitors are able to elicit modulation of both the total levels and the half-life of the c-Myc oncoprotein in cells and also induce apoptosis and loss of cell viability in a range of cancer cell lines. We however observed a narrow therapeutic index compared to a panel of tissue-matched normal cell lines. Thus, it is hoped that these probes and data presented herein will further advance our understanding of the biology and tractability of DUBs as potential future therapeutic targets.

Peripherin/rds is an integral membrane glycoprotein found in the rim regions of vertebrate photoreceptor cell discs. Natural mutations of the encoding gene result in degenerative retinal disorders, such as retinitis pigmentosa. The retinal degeneration slow (rds) phenotype, observed in mice, is considered to be an appropriate model for peripherin/rds-mediated retinitis pigmentosa. Associated abnormalities in the outer segment of photoreceptor cells have implicated peripherin/rds in some aspect of disc morphology, yet it remains unclear whether such morphological effects are the cause or the result of this condition. Here we present the first direct evidence to support a role for peripherin/rds in maintaining the flattened vesicle morphology characteristic of photoreceptor outer segments. In vitro expression yields a 36-kDa immunoreactive species, which is inserted into membranes and undergoes N-glycosylation, inter-and intramolecular disulfide bonding, and dimerization. Electron microscopy reveals that peripherin/rds flattens microsomal vesicles. This effect appears to be dependent on disulfide bond formation but not N-glycosylation. The inability of two pathogenic peripherin/rds mutants (P216L and C165Y) to flatten membrane vesicles implicates such mutations as the primary cause of the retinal degeneration observed in retinitis pigmentosa.The outer segment of the vertebrate rod photoreceptor cell exhibits a highly specialized structure, comprised of a stack of 1000 or more flattened vesicles or discs (1). This organization is vital to the visual process, as it maximizes the area available for photoreception and allows efficient renewal of the photoreceptor outer segments. Any elements involved in the formation and maintenance of this structure are, therefore, of vital importance to the visual process. One protein that has been implicated to have such an involvement is peripherin/rds. Peripherin/rds is a 39-kDa integral membrane glycoprotein localized exclusively to the rim regions of photoreceptor cell discs (2, 3). A topological model has been proposed (4) in which the protein possesses four transmembrane helices and cytosolically oriented N and C termini. The protein has been shown to form disulfide-linked homodimers (2). These peripherin/rds dimers and homodimers of the related disc rim protein ROM-1 (5) are believed to non-covalently associate to form a functional heterotetrameric complex (6, 7).The clinical significance of the human peripherin/rds gene is illustrated by its involvement in a wide range of degenerative retinal disorders, including retinitis pigmentosa (8). To date, over 50 pathogenic mutations within the human gene have been identified. In addition there is a mutation in the murine gene that causes the related disorder, retinal degeneration slow (rds) (9). Phenotypically rds mice exhibit distinctive photoreceptor degeneration (10, 11), and hence, murine rds is considered an important animal model for the inherited human retinal degenerative condition. Mice homozygous for the rds condition ha...

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Aberrant production of amyloid-b peptides by processing of the b-amyloid precursor protein leads to the formation of characteristic extracellular protein deposits which are thought to be the cause of Alzheimer's disease. Therefore, inhibiting the key enzymes responsible for amyloid-b peptide generation, b-and c-secretase may offer an opportunity to intervene with the progression of the disease. In human brain and cell culture systems a heterogeneous population of amyloid-b peptides with various truncations is detected and at present, it is unclear how they are produced. We have used a combination of surface enhanced laser desorption/ionization timeof-flight mass spectrometry (SELDI-TOF MS) and a specific inhibitor of c-secretase to investigate whether the production of all amyloid-b peptide species requires the action of c-secretase. Using this approach, we demonstrate that the production of all truncated amyloid-b peptides except those released by the action of the nonamyloidogenic a-secretase enzyme or potentially beta-site bAPP cleaving enzyme 2 depends on c-secretase activity. This indicates that none of these peptides are generated by a separate enzyme entity and a specific inhibitor of the c-secretase enzyme should have the potential to block the generation of all amyloidogenic peptides. Furthermore in the presence of c-secretase inhibitors, the observation of increased cleavage of the membrane-bound bAPP C-terminal fragment C99 by a-secretase suggests that during its trafficking C99 encounters compartments in which a-secretase activity resides. Keywords: Alzheimer's disease, bAPP processing, c-secretase inhibitor, surface-enhanced laser desorption/ionization time-of-flight mass spectrometry. Amyloid-b (Ab) peptide is the major proteinaceous constituent of extracellular protein deposits which are characteristic of Alzheimer's disease (AD). These deposits occur either as senile plaques in the brain parenchyma or as vascular amyloid around the brain blood vessels (Glenner and Wong 1984;Masters et al. 1985). Ab peptides themselves are generated by processing of the b-amyloid precursor protein (bAPP) (Kang et al. 1987) which requires consecutive cleavages involving b-and c-secretase enzymes (Haass et al. 1992). An alternative processing pathway leads to the release of the bAPP ectodomain as secretory bAPP by cleavage within the Ab domain thereby excluding Ab peptide formation (Weidemann et al. 1989). Members of the disintegrin and metalloprotease family (ADAM) such as ADAM10 and TACE appear to mediate this alternative cleavage termed a-secretase cleavage Lammich et al. 1999). The recently cloned b-secretase enzyme BACE1 (Asp-2) (Hussain et al. 1999;Sinha et al. 1999;Vassar et al. 1999;Yan et al. 1999;Lin et al. 2000) has been shown to generate the membrane bound bAPP C-terminal fragment (C99) intermediate, which is a prerequisite for the release of Ab peptide by c-secretase as the final processing step. BACE1 is the major b-secretase responsible for the generation of Ab peptides by neurones (Cai et al....