Sulfate stabilizes the folding intermediate more than the native structure of endostatin.
Endostatin, a potent angiogenesis inhibitor, is an acid resistant protein with compact tertiary structure. Nuclear magnetic resonance, circular dichroism, and tryptophan emission fluorescence were used to monitor the structural changes of endostatin during acid-, heat-, and urea-induced unfolding processes. Results show that sulfate anions sensitize endostatin to acid, but specifically stabilize it against heat or urea. Moreover, the disappearance of the tertiary structure and the formation of the folding intermediate of endostatin at pH 3.0 are sulfate concentration dependent. These phenomena indicate that sulfate anions stabilize the folding intermediate more than the native structure of endostatin. In addition, heparin shows stronger effect than sodium sulfate on sensitizing endostatin against acid, and very limited stabilizing effect against urea. The loose structure of endostatin upon heparin binding may imply that the physiologically favorable structure for endostatin exerting its biological functions is not as compact as what was reported.
Fu
Yan
Y
Laboratory of Protein Chemistry, Beijing Key Laboratory of Protein Therapeutics, Department of Biological Sciences & Biotechnology, Tsinghua University, Zhongguancun Street, Beijing 100084, PR China.
Wu
Xiaoyu
X
Han
Qing
Q
Liang
Yun
Y
He
Yingbo
Y
Luo
Yongzhang
Y
D000143:Acids / Q000737:chemistry; D020533:Angiogenesis Inhibitors / Q000737:chemistry*; D000838:Anions / Q000737:chemistry; D002942:Circular Dichroism; D043169:Endostatins / Q000737:chemistry*; D006493:Heparin / Q000737:chemistry / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence; D013431:Sulfates / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors; D014508:Urea / Q000737:chemistry
D000143:Acids; D020533:Angiogenesis Inhibitors; D000838:Anions; D043169:Endostatins; D013431:Sulfates; C012036:sodium sulfate; D014508:Urea; D006493:Heparin