Fu Yan, Wu Xiaoyu, Han Qing, Liang Yun, He Yingbo, Luo Yongzhang
Laboratory of Protein Chemistry, Beijing Key Laboratory of Protein Therapeutics, Department of Biological Sciences & Biotechnology, Tsinghua University, Zhongguancun Street, Beijing 100084, PR China.
Arch Biochem Biophys. 2008 Mar 15;471(2):232-9. doi: 10.1016/j.abb.2007.12.011. Epub 2008 Jan 7.
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.
内皮抑素是一种有效的血管生成抑制剂，是一种具有紧密三级结构的耐酸蛋白。利用核磁共振、圆二色性和色氨酸发射荧光来监测内皮抑素在酸、热和尿素诱导的去折叠过程中的结构变化。结果表明，硫酸根阴离子使内皮抑素对酸敏感，但能特异性地使其对热或尿素稳定。此外，在pH 3.0时内皮抑素三级结构的消失和折叠中间体的形成与硫酸根浓度有关。这些现象表明，硫酸根阴离子对内皮抑素折叠中间体的稳定作用大于其天然结构。此外，肝素在使内皮抑素对酸敏感方面比硫酸钠表现出更强的作用，而对尿素的稳定作用非常有限。肝素结合后内皮抑素的结构松散可能意味着内皮抑素发挥其生物学功能的生理适宜结构并不像报道的那样紧密。
