King Abdullah University of Science and Technology

About: King Abdullah University of Science and Technology is a education organization based out in Jeddah, Saudi Arabia. It is known for research contribution in the topics: Membrane & Catalysis. The organization has 6221 authors who have published 22019 publications receiving 625706 citations. The organization is also known as: KAUST.

Mechanistic aspects of carotenoid biosynthesis

Abstract: Carotenoids represent a large class of terpenoids characterized by an extensively conjugated polyene chain. The conjugation system imparts carotenoids with excellent light absorbing properties in the blue-green (450–550 nm) range of the visible spectrum. The light-absorbing properties of carotenoids have been exploited by photosynthetic organisms to extend the range of light absorption by the photosynthetic apparatus beyond that of chlorophyll. 1 Following light absorption the carotenoid excited state undergoes excitation energy transfer to chlorophyll. 2 In addition to their role as accessory pigments, carotenoids protect against excess light by quenching both singlet and triplet state chlorophylls. In plants oxygenated carotenoids, known as xanthophylls, provide additional photoprotective functions by non-photochemical quenching (NPQ) of chlorophyll fluorescence. 2a,3 Carotenoids carry out light independent functions in scavenging peroxyl radicals and preventing oxidative damage particularly against singlet oxygen (1O2).4 Since many organisms and specific animal tissues, such as the macula lutea and the corpus luteum, accumulate large amounts of carotenoids, it was proposed that carotenoids may protect against the damaging effects of oxidative stress in such tissues. 5a,b These properties have prompted much research in the chemopreventative potential of carotenoids. At high oxygen pressures, however, some carotenoids display prooxidative activity4b and some β-carotene formulations have even shown adverse effects in supplementation trials aimed at preventing lung cancer in smokers. 6 The length of the carotenoid polyene chain corresponds to the width of the phospholipid bilayer, which led to the proposal that carotenoids act as “molecular rivets” to stabilize and add rigidity to the phospholipid membrane. 2b,7 The membrane spanning topology could also allow carotenoids to counteract oxidative damage on either side of the membrane. 4b It has also been proposed that membrane-spanning carotenoids can mediate proton transfer across the membrane or serve as transmembrane radical channels. 8 Due to their striking and rich color carotenoids are important floral pigments serving to attract pollinators and seed dispersers. 9 In birds and fish, carotenoids are an important signal of good nutritional condition and are used in ornamental displays as a sign of fitness and to increase sexual attractiveness. 10a,b,c,10d–f Following oxidative cleavage, carotenoids generate apocarotenoid metabolites which serve important signaling and photoreceptive functions. The 11-cis isomers, 11-cis-retinaldehyde, 3,4-didehydro-11-cis-retinaldehyde or 3-hydroxy-11-cis-retinal are used by most animals as a photosensitive moiety coupled to the opsin protein, rhodopsin, cone opsin or melanopsin. 11 These photoreceptor molecules mediate vision and circadian photoentrainment. 12 Bacteria use the light-sensitive carotenoid cleavage product, retinaldehyde, coupled to bacteriorhodopsin and related proteins to transport protons and other ions across the membrane. This ion transport function allows the cell to generate energy, regulate ion balance or sense light. 13a,b,c The acidic forms of several apocarotenoids act as signaling molecules in fungi, plants and vertebrates. The apocarotenoid, trisporic acid, signals mating type in fungi. 14 Plants cleave carotenoids such as 9-cis-neoxanthin to generate the hormone abscisic acid, which plays important roles in inducing seed dormancy, and allowing the plant to adapt to abiotic stress. 15a,b,c Other plant apocarotenoid metabolites, such as strigolactones trigger seed germination of parasitic weeds and inhibit shoot branching. 16 Finally, vertebrates use retinoic acid, a ligand for nuclear receptors to regulate gene transcription in physiological processes that include embryonic development, cell differentiation, and immunity. 17a–c,17d,e Carotenogenesis occurs in all photosynthetic organisms and in some non-photosynthetic bacteria, archaea, protozoa and fungi. Reflecting their ubiquitous presence and pleiotropic roles there are well over 700 different types of carotenoids generated through variations of their pathways of synthesis. 18 There is even recent evidence for the acquisition of carotenogenic enzymes by metazoans through lateral gene transfer from endosymbiotic fungi. 19 Many excellent reviews have focused on the later steps of the carotenoid synthetic pathways and their regulation in bacteria, and plants. 20,21 In this review we concentrate on the mechanisms of carotenoid synthesis by examining the structure and enzymology of enzymes involved in the production of carotenoids starting from the production of isoprenoid precursors.

MoS2 Polymorphic Engineering Enhances Selectivity in the Electrochemical Reduction of Nitrogen to Ammonia

Abstract: The electrochemical N2 reduction reaction (NRR) offers a direct pathway to produce NH3 from renewable energy. However, aqueous NRR suffers from both low Faradaic efficiency (FE) and low yield rate. The main reason is the more favored H+ reduction to H2 in aqueous electrolytes. Here we demonstrate a highly selective Ru/MoS2 NRR catalyst on which the MoS2 polymorphs can be controlled to suppress H+ reduction. A NRR FE as high as 17.6% and NH3 yield rate of 1.14 × 10–10 mol cm–2 s–1 are demonstrated at 50 °C. Theoretical evidence supports a hypothesis that the high NRR activity originates from the synergistic interplay between the Ru clusters as N2 binding sites and nearby isolated S-vacancies on the 2H-MoS2 as centers for hydrogenation; this supports formation of NH3 at the Ru/2H-MoS2 interface.

Adaptation of the genetically tractable malaria pathogen Plasmodium knowlesi to continuous culture in human erythrocytes

Abstract: Research into the aetiological agent of the most widespread form of severe malaria, Plasmodium falciparum, has benefitted enormously from the ability to culture and genetically manipulate blood-stage forms of the parasite in vitro. However, most malaria outside Africa is caused by a distinct Plasmodium species, Plasmodium vivax, and it has become increasingly apparent that zoonotic infection by the closely related simian parasite Plasmodium knowlesi is a frequent cause of life-threatening malaria in regions of southeast Asia. Neither of these important malarial species can be cultured in human cells in vitro, requiring access to primates with the associated ethical and practical constraints. We report the successful adaptation of P. knowlesi to continuous culture in human erythrocytes. Human-adapted P. knowlesi clones maintain their capacity to replicate in monkey erythrocytes and can be genetically modified with unprecedented efficiency, providing an important and unique model for studying conserved aspects of malarial biology as well as species-specific features of an emerging pathogen.

20-meter underwater wireless optical communication link with 1.5 Gbps data rate

Abstract: The video streaming, data transmission, and remote control in underwater call for high speed (Gbps) communication link with a long channel length (~10 meters). We present a compact and low power consumption underwater wireless optical communication (UWOC) system utilizing a 450-nm laser diode (LD) and a Si avalanche photodetector. With the LD operating at a driving current of 80 mA with an optical power of 51.3 mW, we demonstrated a high-speed UWOC link offering a data rate up to 2 Gbps over a 12-meter-long, and 1.5 Gbps over a record 20-meter-long underwater channel. The measured bit-error rate (BER) are 2.8 × 10-5, and 3.0 × 10-3, respectively, which pass well the forward error correction (FEC) criterion.