Chemical Tools for Exploring IFITM3 S-Palmitoylation and Mechanism

Protein S-palmitoylation is a reversible post-translational lipid modification that regulates the trafficking, stability, and activity of proteins in eukaryotes. The detection of fatty-acylated proteins has been challenging but recent advances in chemical labeling methods have enabled more sensitive detection and proteomic analyses, which I summarize in Chapter 1. The proteomic analysis of S-palmitoylated proteins in dendritic cells and macrophages by our laboratory revealed that the interferon-induced transmembrane proteins (IFITMs) are S-fatty-acylated at conserved cysteine (Cys) residues. IFITMs are unique interferon-induced proteins that restrict the infection of multiple pathogenic viruses. Initial studies by our laboratory showed that S-fatty-acylation on three conserved Cys residues were crucial for IFITM3 anti-influenza virus activity. However, endogenous levels and site-specific functions of S-palmitoylation on the individual IFITM3 Cys residues were unknown and are addressed in Chapter 2. In collaboration with other members of the Hang laboratory, we discovered that endogenous IFITM3 is fully S-fatty-acylated in IFN-stimulated mammalian cells and that Cys72 in particular plays an important role in IFITM3 antiviral activity. My additional biochemical studies suggest S-palmitoylation may regulate IFITM3 protein turnover in mammalian cells. IFITMs appear to inhibit virus entry into mammalian cells, but the precise mechanisms have been unclear due to limited methods for live-cell imaging and IFITM3 protein-protein interaction studies. To address these limitations, I explored amber codon suppression technology for site-specific IFITM3 labeling with unnatural amino acids for bioorthogonal imaging and covalent protein crosslinking in mammalian cells in Chapter 3. Using the pyrrolysyl-tRNA synthetase (PylRS)/Pyl tRNACUA system, I showed that unnatural amino acid can be site-specifically incorporated throughout IFITM3 in mammalian cells. The site-specific labeling of IFITM3 with unnatural amino acids has provided new opportunities for live-cell imaging and photocrosslinking studies with specific interacting proteins in Chapter 4. My thesis studies have revealed additional insight into IFITM3 regulation by S-palmitoylation and established new tools to explore the antiviral mechanism of IFITMs

Distinguishing Attacks on MAC/HMAC Based on A New Dedicated Compression Function Framework

A new distinguishing attack on HMAC and NMAC based on a dedicated compression function framework H, proposed in ChinaCrypt2008, is first presented in this paper, which distinguish the HMAC/NMAC-H from HMAC/NMAC with a random function. The attack needs 2^{17} chosen messages and 223 queries, with a success rate of 0.873. Furthermore, according to distinguishing attack on SPMAC-H, a key recovery attack on the SPMAC-H is present, which recover all 256-bit key with 2^{17)chosen messages, 2^{19} queries, and (t+1)x8 times decrypting algorithms

Arctic warming-induced cold damage to East Asian terrestrial ecosystems

The global mean temperature is increasing due to the increase in greenhouse gases in the atmosphere, but paradoxically, many regions in the mid-latitudes have experienced cold winters recently. Here we analyse multiple observed and modelled datasets to evaluate links between Arctic temperature variation and cold damage in the East Asian terrestrial ecosystem. We find that winter warming over the Barents-Kara Sea has led to simultaneous negative temperature anomalies over most areas in East Asia and negative leaf area index anomalies in southern China where mostly subtropical evergreen forests are growing. In addition to these simultaneous impacts, spring vegetation activity and gross primary productivity were also reduced over evergreen and deciduous trees, and spring phenological dates are delayed. Earth System model simulations reveal that cold damage becomes stronger under greenhouse warming; therefore Arctic warming-induced cold stress should be considered in forest and carbon management strategies

Generation of cardiomyocytes from human-induced pluripotent stem cells resembling atrial cells with ability to respond to adrenoceptor agonists

Atrial fibrillation (AF) is the most common chronic arrhythmia presenting a heavy disease burden. We report a new approach for generating cardiomyocytes (CMs) resembling atrial cells from human-induced pluripotent stem cells (hiPSCs) using a combination of Gremlin 2 and retinoic acid treatment. More than 40% of myocytes showed rod-shaped morphology, expression of CM proteins (including ryanodine receptor 2, α-actinin-2 and F-actin) and striated appearance, all of which were broadly similar to the characteristics of adult atrial myocytes (AMs). Isolated myocytes were electrically quiescent until stimulated to fire action potentials with an AM profile and an amplitude of approximately 100 mV, arising from a resting potential of approximately −70 mV. Single-cell RNA sequence analysis showed a high level of expression of several atrial-specific transcripts including NPPA, MYL7, HOXA3, SLN, KCNJ4, KCNJ5 and KCNA5. Amplitudes of calcium transients recorded from spontaneously beating cultures were increased by the stimulation of α-adrenoceptors (activated by phenylephrine and blocked by prazosin) or β-adrenoceptors (activated by isoproterenol and blocked by CGP20712A). Our new approach provides human AMs with mature characteristics from hiPSCs which will facilitate drug discovery by enabling the study of human atrial cell signalling pathways and AF. This article is part of the theme issue ‘The heartbeat: its molecular basis and physiological mechanisms’

Crystal Structure of the Caenorhabditis elegans Apoptosome Reveals an Octameric Assembly of CED-4

SummaryThe CED-4 homo-oligomer or apoptosome is required for initiation of programmed cell death in Caenorhabditis elegans by facilitating autocatalytic activation of the CED-3 caspase zymogen. How the CED-4 apoptosome assembles and activates CED-3 remains enigmatic. Here we report the crystal structure of the complete CED-4 apoptosome and show that it consists of eight CED-4 molecules, organized as a tetramer of an asymmetric dimer via a previously unreported interface among AAA+ ATPases. These eight CED-4 molecules form a funnel-shaped structure. The mature CED-3 protease is monomeric in solution and forms an active holoenzyme with the CED-4 apoptosome, within which the protease activity of CED-3 is markedly stimulated. Unexpectedly, the octameric CED-4 apoptosome appears to bind only two, not eight, molecules of mature CED-3. The structure of the CED-4 apoptosome reveals shared principles for the NB-ARC family of AAA+ ATPases and suggests a mechanism for the activation of CED-3

A Cross-layer Scheduling Algorithm Based on Cognitive Radio Network

Abstract: Cognitive radio network users have different QoS requirements. In order to provide different QoS requirements to users as well as increase the capacities of the cognitive radio networks, this paper presents a first in-depth comparative study on different factors effect QoS which include system performance, power interference, wireless channel conditions, services priorities and fairness constraints. A cross-layer scheduling algorithm which could optimize system performance and control power interference is proposed. Latency default probability of real-time users and throughput performance of non- real-time users are respectively used to measure the fairness of real-time operational system and non-real-time operational system. Simulation results are computed and the results are shown. Delay performance of real-time traffic and throughput performance of non-real-time traffic are guaranteed by setting reasonable weight to index. And power interference to authorized users caused by cognitive radio network users reduces obviously. And system obtains a very good fair performance

Effects of temperature and precipitation on litterfall phenology in four evergreen broad-leaved forests of southern China

Vegetative and reproductive growth of subtropical and tropical forests plays an important role in regulating carbon cycle and maintaining food web dynamic balance. Here, we used litterfall and climatic data during 1998–2017 at four evergreen forest sites in southern China to analyze temporal variations of community phenology and their climate drivers. Results show that two southwest forests have unimodal patterns with leaf litterfall peaks during dry season, while two southeast forests have bimodal patterns with the first peaks during rainy season and the second peaks during rainy and dry seasons respectively. Peaks of flower litterfall for the four forests occurred during the transitional period between dry and rainy seasons, while peaks of fruit litterfall appeared either at the end of the rainy season at the two southern sites or in the dry season at the two northern sites. Leaf litterfall correlates significantly positively with preseason maximum temperature at the four sites, but significantly negatively with preseason precipitation at two southwest sites. By contrast, flower and fruit litterfall correlates significantly positively with preseason temperature and precipitation at only three and two sites. Moreover, leaf, flower, and fruit litterfall exhibits a 12-month cycle, which is consistent with the 12-month cycle of monthly temperature and precipitation. Flower and fruit litterfall displays also multiyear cycles between 18 and 48 months, however, it is inconsistent with the multiyear cycles of monthly temperature and precipitation. Our study highlights that temperature and precipitation are key factors affecting litterfall variations in different time scales in southern China