Rodgers R E, Consigli R A
Division of Biology, Kansas State University, Manhattan 66506, USA.
Virus Res. 1996 Oct;44(2):123-35. doi: 10.1016/0168-1702(96)01349-4.
Calcium ions appear to play a major role in maintaining the structural integrity and assembly of papovavirus virions and are likely involved in the process of viral uncoating. Recently it was reported that the purified recombinant VP1 protein of budgerigar fledgling disease virus (BFDV) was capable of assembling into capsid-like particles in the presence of calcium. It is now reported that the major capsid protein VP1 of BFDV binds calcium ions in an in vitro calcium binding assay. Two deletions were made in the VP1 protein to identify a calcium binding domain and to further characterize the role of calcium ions in the capsid assembly process. Recombinant VP1 lacking a putative calcium binding domain (Asp-237-Asp-248) failed to bind radioactive 45Ca2+ yet associated into capsomeres. These capsomeres were similar in shape to the wild-type VP1 but were unable to assemble into capsid-like particles. Likewise, recombinant VP1 lacking ten carboxyl terminal amino acids (Glu-334-Arg-343) also formed capsomeres that were unable to assemble into capsid-like particles. In contrast to the VP1 protein with the internal deletion, the protein with the truncated carboxyl terminus bound 45Ca2+ in the in vitro assay. These results have identified a calcium binding domain (Asp-237-Asp-248) for the BFDV VP1 protein and a crucial role for the VP1 carboxyl terminal amino acids (Glu-334-Arg-343) in capsid assembly.
钙离子似乎在维持乳头多瘤空泡病毒病毒粒子的结构完整性和组装过程中发挥着重要作用，并且可能参与病毒脱壳过程。最近有报道称，在有钙离子存在的情况下，虎皮鹦鹉幼雏病病毒（BFDV）纯化的重组VP1蛋白能够组装成衣壳样颗粒。现在有报道称，在体外钙离子结合试验中，BFDV的主要衣壳蛋白VP1能结合钙离子。在VP1蛋白上进行了两处缺失，以确定钙离子结合结构域，并进一步阐明钙离子在衣壳组装过程中的作用。缺乏假定钙离子结合结构域（Asp-237-Asp-248）的重组VP1未能结合放射性45Ca2+，但能组装成壳粒。这些壳粒的形状与野生型VP1相似，但无法组装成衣壳样颗粒。同样，缺少十个羧基末端氨基酸（Glu-334-Arg-343）的重组VP1也形成了无法组装成衣壳样颗粒的壳粒。与具有内部缺失的VP1蛋白相反，在体外试验中，具有截短羧基末端的蛋白能结合45Ca2+。这些结果确定了BFDV VP1蛋白的一个钙离子结合结构域（Asp-237-Asp-248），以及VP1羧基末端氨基酸（Glu-334-Arg-343）在衣壳组装中的关键作用。
