Subjects: Biology >> Biophysics submitted time 2016-05-12
Abstract： The (3R)-hydroxyacyl-ACP dehydratase HadAB, involved in the biosynthetic pathway for mycolic acid (MA) of Mycobacterium tuberculosis, catalyzes the third step in the fatty acid (FA) elongation cycle, which is an ideal and actual target for anti-tubercular agent. Though HadAB is predicted to be a member of the hotdog superfamily, it shares no sequence identity with typical hotdog fold isoenzyme FabZ. To characterize the significance of HadAB from the perspective of structural biology, large amount of pure HadAB complex is required for biochemical characterization and crystallization. Here, we used a unique expression and purification method. HadA and HadB were cloned separately and co-expressed in Escherichia coli. After GST affinity chromatography, two steps of anion exchange chromatography and gel filtration, the purity of the protein as estimated by SDS-PAGE was >95%. Using hanging-drop vapor-diffusion method, crystals were obtained and diffracted X-rays to 1.75 angstrom resolution. The crystal belongs to space group P4(1)2(1)2, with unit-cell parameters a = b = 82.0 angstrom, c = 139.8 angstrom, alpha = beta = gamma = 90.0 degrees. (C) 2015 The Authors. Published by Elsevier Inc.
Peer Review Status:
Awaiting Review
Subjects: Biology >> Biophysics submitted time 2016-05-12
Abstract： Pneumolysin is one of the major virulence factors elaborated by Streptococcus pneumoniae; this toxin is a member of the cholesterol-dependent cytolysins. Engagement of cholesterol induces the formation of a multi-subunit complex by pneumolysin that lyses host cells by forming pores on the membrane. Because pneumolysin released by bacteria which have been killed by conventional antibiotics is still active, agents capable of directly attacking the toxin are considered advantageous against antimicrobials in the treatment of S. pneumoniae infections. Here we found that the phytosterol, beta-sitosterol, effectively protects against cell lysis caused by pneumolysin. This compound interacts with the toxin at Thr459 and Leu460, two sites important for being recognized by its natural ligand, cholesterol. Similar to cholesterol, beta-sitosterol induces pneumolysin oligomerization. This compound also protects cells from damage by other cholesterol-dependent toxins. Finally, this compound protects mice against S. pneumoniae infection. Thus, beta-sitosterol is a candidate for the development of anti-virulence agents against pathogens that rely on cholesterol-dependent toxins for successful infections.
Peer Review Status:Awaiting Review
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