The complete biosynthesis of the genetically encoded amino acid pyrrolysine from lysine

Pyrrolysine, the twenty-second amino acid found to be encoded in the natural genetic code, is necessary for all of the known pathways by which methane is formed from methylamines. Pyrrolysine comprises a methylated pyrroline carboxylate in amide linkage to the ε-amino group of L-lysine. In certain Archaea, three methyltransferases initiate methanogenesis from the various methylamines, and these enzymes are encoded by genes with an in-frame amber codon that is translated as pyrrolysine. Escherichia coli that has been transformed with the pylTSBCD genes from methanogenic Archaea can incorporate endogenously biosynthesized pyrrolysine into proteins. The decoding of UAG as pyrrolysine requires pylT, which produces tRNA(Pyl) (also called tRNA(CUA)), and pylS, which encodes a pyrrolysyl-tRNA synthetase. The pylB, pylC and pylD genes are each required for tRNA-independent pyrrolysine synthesis. Pyrrolysine is the last remaining genetically encoded amino acid with an unknown biosynthetic pathway. Here we provide genetic and mass spectrometric evidence for a pylBCD-dependent pathway in which pyrrolysine arises from two lysines. We show that a newly uncovered UAG-encoded amino acid, desmethylpyrrolysine, is made from lysine and exogenous D-ornithine in a pylC-dependent process followed by a pylD-dependent process, but it is not further converted to pyrrolysine. These results indicate that the radical S-adenosyl-L-methionine (SAM) protein PylB mediates a lysine mutase reaction that produces 3-methylornithine, which is then ligated to a second molecule of lysine by PylC before oxidation by PylD results in pyrrolysine. The discovery of lysine as the sole precursor to pyrrolysine will further inform discussions of the evolution of the genetic code and amino acid biosynthetic pathways. Furthermore, intermediates of the pathway may provide new avenues by which the pyl system can be exploited to produce recombinant proteins with useful modified residues.     

A cellular oncogene (c-Ki-ras) is amplified, overexpressed, and located within karyotypic abnormalities in mouse adrenocortical tumour cells

The cellular oncogene c-Ki-ras is amplified 30- to 60-fold in cells of the mouse adrenocortical tumour Y1. The amplified oncogene is located in double minute chromosomes and in a homogeneously staining chromosomal region, common karyotypical anomalies of tumour cells. The amounts of c-Ki-ras specific mRNA and of the protein (p21) encoded by the amplified gene are correspondingly elevated. Amplification and enhanced expression of cellular oncogenes may contribute to the genesis and/or maintenance of at least some naturally occurring tumours.     

Perspectives on executive information systems

Executives who consider the acquisition of Executive Information Systems (EIS) may encounter several major problems already in their selection and introduction stages. Key issues are the following: Can the EIS's really match our managerial needs and support decision making in our organizational contingencies? How widely in the leadership levels can they be introduced? Are they easy-to-learn, easy-to-use and easily customizable? Do they utilize the newest information technology, e.g. graphics and modern interface technology? Can they work in our computer network? In order to facilitate elegant solutions of the selection problems, we construct an evaluation framework which guides the selection of an EIS product to match the managerial needs according to the organizational contingencies. This framework is useful immediately after the specification of the decision making support requirements of the executive. The effectiveness of the framework is shown by applying it and analyzing 13 EIS products. We also offer introduction and use experiences from four English and four Finnish large companies covering the opinions of 132 EIS users. In this paper we give general answers to the questions above and discuss other relevant issues.     

A mutation in APP protects against Alzheimer's disease and age-related cognitive decline

The prevalence of dementia in the Western world in people over the age of 60 has been estimated to be greater than 5%, about two-thirds of which are due to Alzheimer's disease. The age-specific prevalence of Alzheimer's disease nearly doubles every 5 years after age 65, leading to a prevalence of greater than 25% in those over the age of 90 (ref. 3). Here, to search for low-frequency variants in the amyloid-β precursor protein (APP) gene with a significant effect on the risk of Alzheimer's disease, we studied coding variants in APP in a set of whole-genome sequence data from 1,795 Icelanders. We found a coding mutation (A673T) in the APP gene that protects against Alzheimer's disease and cognitive decline in the elderly without Alzheimer's disease. This substitution is adjacent to the aspartyl protease β-site in APP, and results in an approximately 40% reduction in the formation of amyloidogenic peptides in vitro. The strong protective effect of the A673T substitution against Alzheimer's disease provides proof of principle for the hypothesis that reducing the β-cleavage of APP may protect against the disease. Furthermore, as the A673T allele also protects against cognitive decline in the elderly without Alzheimer's disease, the two may be mediated through the same or similar mechanisms.     

Common variants on 8p12 and 1q24.2 confer risk of schizophrenia

Schizophrenia is a severe mental disorder affecting ～1% of the world population, with heritability of up to 80%. To identify new common genetic risk factors, we performed a genome-wide association study (GWAS) in the Han Chinese population. The discovery sample set consisted of 3,750 individuals with schizophrenia and 6,468 healthy controls (1,578 cases and 1,592 controls from northern Han Chinese, 1,238 cases and 2,856 controls from central Han Chinese, and 934 cases and 2,020 controls from the southern Han Chinese). We further analyzed the strongest association signals in an additional independent cohort of 4,383 cases and 4,539 controls from the Han Chinese population. Meta-analysis identified common SNPs that associated with schizophrenia with genome-wide significance on 8p12 (rs16887244, P = 1.27 × 10(-10)) and 1q24.2 (rs10489202, P = 9.50 × 10(-9)). Our findings provide new insights into the pathogenesis of schizophrenia.     

A rare variant in MYH6 is associated with high risk of sick sinus syndrome

Through complementary application of SNP genotyping, whole-genome sequencing and imputation in 38,384 Icelanders, we have discovered a previously unidentified sick sinus syndrome susceptibility gene, MYH6, encoding the alpha heavy chain subunit of cardiac myosin. A missense variant in this gene, c.2161C>T, results in the conceptual amino acid substitution p.Arg721Trp, has an allelic frequency of 0.38% in Icelanders and associates with sick sinus syndrome with an odds ratio = 12.53 and P = 1.5 × 10?2?. We show that the lifetime risk of being diagnosed with sick sinus syndrome is around 6% for non-carriers of c.2161C>T but is approximately 50% for carriers of the c.2161C>T variant.     

Blocking VEGFR-3 suppresses angiogenic sprouting and vascular network formation

Angiogenesis, the growth of new blood vessels from pre-existing vasculature, is a key process in several pathological conditions, including tumour growth and age-related macular degeneration. Vascular endothelial growth factors (VEGFs) stimulate angiogenesis and lymphangiogenesis by activating VEGF receptor (VEGFR) tyrosine kinases in endothelial cells. VEGFR-3 (also known as FLT-4) is present in all endothelia during development, and in the adult it becomes restricted to the lymphatic endothelium. However, VEGFR-3 is upregulated in the microvasculature of tumours and wounds. Here we demonstrate that VEGFR-3 is highly expressed in angiogenic sprouts, and genetic targeting of VEGFR-3 or blocking of VEGFR-3 signalling with monoclonal antibodies results in decreased sprouting, vascular density, vessel branching and endothelial cell proliferation in mouse angiogenesis models. Stimulation of VEGFR-3 augmented VEGF-induced angiogenesis and sustained angiogenesis even in the presence of VEGFR-2 (also known as KDR or FLK-1) inhibitors, whereas antibodies against VEGFR-3 and VEGFR-2 in combination resulted in additive inhibition of angiogenesis and tumour growth. Furthermore, genetic or pharmacological disruption of the Notch signalling pathway led to widespread endothelial VEGFR-3 expression and excessive sprouting, which was inhibited by blocking VEGFR-3 signals. Our results implicate VEGFR-3 as a regulator of vascular network formation. Targeting VEGFR-3 may provide additional efficacy for anti-angiogenic therapies, especially towards vessels that are resistant to VEGF or VEGFR-2 inhibitors.