Saul F A, Vulliez-le Normand B, Lema F, Bentley G A
Institut Pasteur, Unité d'Immunologie Structurale, C.N.R.S. U.R.A. 1961, Paris, France.
Proteins. 1997 Jan;27(1):1-8. doi: 10.1002/(sici)1097-0134(199701)27:1<1::aid-prot2>3.0.co;2-l.
We report the crystal structure of MalE-B133, a recombinant form of the maltodextrin-binding protein (MBP) of Escherichia coli carrying an inserted amino-acid sequence of a B-cell epitope from the preS2 region of the hepatitis B virus (HBV). The structure was determined by molecular replacement methods and refined to 2.7 A resolution. MalE-B133 is an insertion/deletion mutant of MBP in which residues from positions 134 to 142, an external alpha helix in the wild-type structure, are replaced by a foreign peptide segment of 19 amino acids. The inserted residues correspond to the preS2 sequence from positions 132 to 145 and five flanking residues that arise from the creation of restriction sites. The conformation of the recombinant protein, excluding the inserted segment, closely resembles that of wild-type MBP in the closed maltose-bound form. MalE-B133 was shown by previous studies to display certain immunogenic and antigenic properties of the hepatitis B surface antigen (HBsAg), which contains the preS2 region. The crystal structure reveals the conformation of the first nine epitope residues (preS2 positions 132 to 140) exposed on the surface of the molecule. The remaining five epitope residues (preS2 positions 141 to 145) are not visible in electron density maps. The path of the polypeptide chain in the visible portion of the insert differs from that of the deleted segment in the structure of wild-type MBP, displaying a helical conformation at positions 134 to 140 (preS2 sequence numbering). A tripeptide (Asp-Pro-Arg) at the N terminus of the helix forms a stable structural motif that may be implicated in the cross-reactivity of anti-HBsAg antibodies with the hybrid protein.
我们报道了MalE-B133的晶体结构，它是大肠杆菌麦芽糖糊精结合蛋白（MBP）的重组形式，携带来自乙型肝炎病毒（HBV）前S2区的B细胞表位的插入氨基酸序列。该结构通过分子置换方法确定，并精修至2.7 Å分辨率。MalE-B133是MBP的插入/缺失突变体，其中野生型结构中第134至142位的残基（一个外部α螺旋）被19个氨基酸的外源肽段取代。插入的残基对应于前S2序列中第132至145位以及因限制性酶切位点产生而出现的五个侧翼残基。重组蛋白（不包括插入片段）的构象与处于结合麦芽糖的封闭形式的野生型MBP非常相似。先前的研究表明，MalE-B133具有包含前S2区的乙型肝炎表面抗原（HBsAg）的某些免疫原性和抗原性。晶体结构揭示了分子表面暴露的前九个表位残基（前S2序列第132至140位）的构象。其余五个表位残基（前S2序列第141至145位）在电子密度图中不可见。插入片段可见部分的多肽链路径与野生型MBP结构中缺失片段的路径不同，在第134至140位（以前S2序列编号）呈现螺旋构象。螺旋N端的一个三肽（天冬氨酸-脯氨酸-精氨酸）形成一个稳定的结构基序，可能与抗HBsAg抗体与杂合蛋白的交叉反应有关。
