254 research outputs found
Crystal Structures of Cobalamin-Independent Methionine Synthase (MetE) from Streptococcus mutans: A Dynamic Zinc-Inversion Model
No full textCobalamin-independent methionine synthase (MetE) catalyzes the direct transfer of a methyl group from methyltetrahydrofolate to L-homocysteine to form methionine. Previous studies have shown that the MetE active site coordinates a zinc atom, which is thought to act as a Lewis acid and plays a role in the activation of thiol. Extended X-ray absorption fine structure studies and mutagenesis experiments identified the zinc-binding site in MetE from Escherichia coli. Further structural investigations of MetE from Thermotoga maritima lead to the proposition of two models: "induced fit" and "dynamic equilibrium", to account for the catalytic mechanisms of MetE. Here, we present crystal structures of oxidized and zinc-replete MetE from Streptococcus mutans at the physiological pH. The structures reveal that zinc is mobile in the active center and has the possibility to invert even in the absence of homocysteine. These structures provide evidence for the dynamic equilibrium model. (C) 2011 Elsevier Ltd. All rightshttp://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000295496500012&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Biochemistry & Molecular BiologySCI(E)PubMed7ARTICLE4688-69741
An IBC and certificate based hybrid approach to WIMAX security
No full textWiMAX is a promising technology that provides high data throughput with low delays for various user types and modes of operation. These advantages make WiMAX applicable both for infrastructure purposes and end-client usage. Since WiMAX is presented as a network framework and a last-mile technology, it is believed to be capable of handling a wide range of usage scenarios. For example, while the end users have an opportunity to use WiMAX as the primary connection medium for acquiring services such as on-demand video streaming, VoIP connections and mobile bank transactions, the service providers may use it for data relaying purposes among access points. To meet the technical requirements of these various scenarios, majority of the WiMAX research has been conducted on physical and MAC layers; however little has been invested in a comprehensive and efficient security solution, which has resulted in a wide range of security weaknesses and reactive solutions. Many security problems remain to be addressed in different modes and for different user types even in the final security standard of WiMAX, PKMv2. In this thesis, we present a hybrid security solution combining Identity-Based Cryptography (IBC) and certificate based approaches to overcome the existing security problems of WiMAX without degrading service quality. IBC has potential benefits that can provide enhancements to the overall security and efficiency of the security standard. One such enhancement is combining user identity with the public key and therefore eliminating the public key distribution load from the network. However, IBC has a few caveats, such as the necessity of a secure medium to distribute private keys. To compensate for these disadvantages, in this study, IBC is combined with certificate-based security. As a result, the benefits of IBC are maintained while the disadvantages are eliminated. Using the hybrid approach, this study also aims to clarify the key revocation procedures and key lifetimes of WiMAX. To achieve this goal, key renewal intervals are examined and corresponding lifetimes are assigned to the credentials missing in both PKMv2 and PKMv1. Additionally, the key distribution procedures are investigated and a pattern is provided with the message exchange details. To be able to correctly assess the efficiency of this approach, a new mobility model is defined in the evaluation chapter of this thesis. Based on this model, the analysis has shown that our hybrid solution that combines IBC and the certified based security scheme results in a significant bandwidth improvement over the standard’s approach, PKMv2. This work is the first study that unites the advantages of both IBC and the certified-based security scheme for improved security while maintaining low overhead for WiMAX.M.S.Includes bibliographical referencesIncludes abstrac
Occult Hepatitis B and Risk of Reactivation After Hepatitis C Treatment With Direct-Acting Antivirals
No full text
Resolved hepatitis B virus infection: an unresolved issue of terminology
No full textWOS: 000446527500019PubMed ID: 30252716
A meningitis case due to Stenotrophomonas maltophilia and review of the literature
No full textSummaryStenotrophomonas maltophilia (formerly Xanthomonas maltophilia) is a Gram-negative bacillus increasingly associated with serious nosocomial infections. Here, we describe a 30-year-old male patient who developed meningitis associated with this organism after several neurosurgical procedures. A review of the literature revealed only 15 previous reports. Most cases were associated with neurosurgical procedures. Antimicrobial therapy is complicated by multiple drug resistance of the organism, and trimethoprim–sulfamethoxazole is the recommended agent for treatment
Does resolved HBV or anti-HBc-only carry the same risk of HBV reactivation?
No full textWOS: 000441723400010PubMed ID: 29925293
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