Lou Y C, Lin I J, Pai M T, Cheng J W
Department of Life Science, National Tsing Hua University, Taiwan, Republic of China.
Arch Biochem Biophys. 2000 May 15;377(2):219-27. doi: 10.1006/abbi.2000.1797.
Hepatitis delta virus (HDV) is a satellite virus of the hepatitis B virus (HBV) which provides the surface antigen for the viral coat. The RNA genome of HDV encodes two proteins, the small delta antigen and the large delta antigen, which differ only with the latter having an additional 19 amino acids at the C-terminus. Previously, we have shown that dAg24-50, a synthetic peptide corresponding to residues 24-50 of the N-terminal leucine-repeat region of hepatitis delta antigen, binds to the viral RNA and forms an alpha-helical conformation in TFE-containing solution. However, it exhibited low alpha-helicity (less than 5%) in the absence of TFE. In order to obtain biologically active delta antigen peptides with higher structural stability in solution, an N-capping 21-residue polypeptide corresponding to residues 24-38 of hepatitis delta antigen (dAg(Cap24-38am)) was synthesized and, surprisingly, its solution structure was found to be a stable alpha-helix (64%) by circular dichroism and 1H NMR techniques. Moreover, the structure of the capping box shows the characteristic L-shaped bend perpendicular to the helix axis. This structural knowledge provides a molecular basis for understanding the role of the N-terminal leucine-repeat region of hepatitis delta antigen and has a significant potential for the development of diagnostic and therapeutic methods for HDV.
丁型肝炎病毒（HDV）是乙型肝炎病毒（HBV）的卫星病毒，HBV为HDV病毒衣壳提供表面抗原。HDV的RNA基因组编码两种蛋白质，即小δ抗原和大δ抗原，二者的区别仅在于后者在C末端多了19个氨基酸。此前，我们已经表明，dAg24 - 50（一种与丁型肝炎抗原N端亮氨酸重复区域的24 - 50位残基相对应的合成肽）能与病毒RNA结合，并在含TFE的溶液中形成α螺旋构象。然而，在没有TFE的情况下，它表现出较低的α螺旋度（小于5%）。为了获得在溶液中具有更高结构稳定性的具有生物活性的δ抗原肽，合成了一种与丁型肝炎抗原24 - 38位残基相对应的N - 封端21残基多肽（dAg(Cap24 - 38am)），令人惊讶的是，通过圆二色性和1H NMR技术发现其溶液结构是稳定的α螺旋（64%）。此外，封端盒的结构显示出垂直于螺旋轴的特征性L形弯曲。这一结构知识为理解丁型肝炎抗原N端亮氨酸重复区域的作用提供了分子基础，并且在HDV诊断和治疗方法的开发方面具有巨大潜力。
