title: Deficiency of disulfide bonds facilitating fibrillogenesis of endostatin.
abstract: Endostatin is an endogenous inhibitor of tumor angiogenesis and tumor growth. It has two pairs of disulfide bonds in a unique nested pattern, which play a key role in its native conformation, stability, and activity. Here, we constructed a disulfide-deficient variant of endostatin, endo-all-Ala, to examine the effects of the two disulfide bonds on fibrillogenesis of endostatin under nondenaturing conditions. Based on thioflavin T fluorescence, atomic force microscopy, far-UV circular dichroism, and Fourier transform infrared spectroscopy, we found that endo-all-Ala, which has a higher alpha-helical content compared with wild type, is prone to forming fibrils in a pH-dependent manner. Subsequently, more hydrophobic patches with a lower stability of endo-all-Ala were observed when compared with wild type, which possibly contributes to the propensity of amyloid formation of endo-all-Ala. To our surprise, the significant increase of the alpha-helical content in endostatin induced by trifluoroethanol can also facilitate fibril formation. In addition, the cytotoxicity of fibrillar aggregates of endo-all-Ala, which were generated at different stages of the fibril formation process, was evaluated by cell viability assay. The results indicate that the cytotoxicity is not due to the fibrils but rather due to the granular aggregates of endo-all-Ala. Moreover, endostatin was interestingly found to be reduced by glutathione at physiological concentrations. Our present work not only elucidates the correlation between the existence of disulfide bonds and the fibril formation of endostatin but also may provide some insights into the structural and functional basis of endostatin in Alzheimer disease brains.
authors.affiliation: Laboratory of Protein Chemistry, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, China.
authors.forename: Yingbo
authors.initials: Y
authors.lastname: He
authors.forename: Hao
authors.initials: H
authors.lastname: Zhou
authors.forename: Huadong
authors.initials: H
authors.lastname: Tang
authors.forename: Yongzhang
authors.initials: Y
authors.lastname: Luo
mesh_terms: D000409:Alanine / Q000737:chemistry; D000544:Alzheimer Disease / Q000378:metabolism; D000818:Animals; D052160:Benzothiazoles; D002470:Cell Survival; D002942:Circular Dichroism; D004220:Disulfides / Q000737:chemistry; D043169:Endostatins / Q000737:chemistry*; D004926:Escherichia coli / Q000378:metabolism; D024021:Fibril-Associated Collagens / Q000737:chemistry*; D005456:Fluorescent Dyes / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008027:Light; D018625:Microscopy, Atomic Force; D009389:Neovascularization, Pathologic; D016716:PC12 Cells; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D051381:Rats; D012542:Scattering, Radiation; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature; D013778:Tetrazolium Salts / Q000494:pharmacology; D013844:Thiazoles / Q000737:chemistry / Q000494:pharmacology; D013997:Time Factors; D014364:Tryptophan / Q000737:chemistry; D014466:Ultraviolet Rays
chemical_list: D052160:Benzothiazoles; D004220:Disulfides; D043169:Endostatins; D024021:Fibril-Associated Collagens; D005456:Fluorescent Dyes; D013778:Tetrazolium Salts; D013844:Thiazoles; C009462:thioflavin T; D014364:Tryptophan; C022616:thiazolyl blue; D005978:Glutathione; D000409:Alanine