分类： 生物学 >> 生物物理学 提交时间： 2016-05-12
摘要： 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.
分类： 生物学 >> 生物物理学 提交时间： 2016-05-12
Wang, Weiyi
Wei, Suning
Su, Xueying
Du, Congkuo
Li, Fengjuan
Geng, Bin
Xu, Guoheng
Li, Linghai
Liu, Pingsheng
摘要： Testicular Leydig cells contain abundant cytoplasmic lipid droplets (LDs) as a cholesteryl-ester store for releasing cholesterols as the precursor substrate for testosterone biosynthesis. Here, we identified the protein composition of testicular LDs purified from adult mice by using mass spectrometry and immunodetection. Among 337 proteins identified, 144 were previously detected in LD proteomes; 44 were confirmed by microscopy. Testicular LDs contained multiple Rab GTPases, chaperones, and proteins involved in glucuronidation, ubiquination and transport, many known to modulate LD formation and LD-related cellular functions. In particular, testicular LDs contained many members of both the perilipin family and classical lipase/esterase superfamily assembled predominately in adipocyte LDs. Thus, testicular LDs might be regulated similar to adipocyte LDs. Remarkably, testicular LDs contained a large number of classical enzymes for biosynthesis and metabolism of cholesterol and hormonal steroids, so steroidogenic reactions might occur on testicular LDs or the steroidogenic enzymes and products could be transferred through testicular LDs. These characteristics differ from the LDs in most other types of cells, so testicular LDs could be an active organelle functionally involved in steroidogenesis.
分类： 生物学 >> 生物物理学 提交时间： 2016-05-12
Ma, Haihao
Ma, Yuemin
Liu, Kaiyu
Peng, Jianxin
Peng, Rong
Liu, Xuehui
Xu, Pingyong
Dyer, David H.
Lan, Que
Hong, Huazhu
摘要： The cotton bollworm, Helicoverpa armigera, has developed strong resistance to many insecticides. Sterol Carrier Protein-2 (SCP-2) is an important non-specific lipid transfer protein in insects and appears to be a potential new target. In order to elucidate the structure and function of Helicoverpa armigera SCP-2 (HaSCP-2), NMR spectroscopy, docking simulations, mutagenesis and bioassays were performed. HaSCP-2 composed of five alpha-helices and four stranded beta-sheets. The folds of alpha-helices and beta-sheets interacted together to form a hydrophobic cavity with putative entrance and exit openings, which served as a tunnel for accommodating and transporting of lipids. Several sterols and fatty acids could interact with HaSCP-2 via important hydrophobic sites, which could be potential targets for insecticides. Mutagenesis experiments indicated Y51, F53, F89, F110, I117 and Q131 may be the key functional sites. HaSCP-2 showed high cholesterol binding activity and SCP-2 inhibitors (SCPIs) could inhibit the biological activity of HaSCP-2. SCPI-treated larvae at young stage showed a significant decrease of cholesterol uptake in vivo. Our study describes for the first time a NMR structure of SCP-2 in lepidopteran H. armigera and reveals its important function in cholesterol uptake, which facilitates the screening of effective insecticides targeting the insect cholesterol metabolism.
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