Weak protein-protein interactions are sufficient to drive assembly of hepatitis B virus capsids
Weak protein-protein interactions are sufficient to drive assembly of hepatitis B virus capsids
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DOI：
10.1021/bi0261645
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发表时间：
2002-10-01
期刊：
影响因子：
2.9
通讯作者：
Zlotnick, A
中科院分区：
文献类型：
--
作者：
Ceres, P;Zlotnick, A
B型肝炎病毒（HBV）是一种具有球形衣壳（或核心）的包膜DNA病毒。衣壳由以T = 4二十面体对称性排列的120个拷贝的同二聚体衣壳蛋白构建。我们检测了纯化的E.在大肠杆菌中表达HBV衣壳蛋白。平衡后，通过尺寸排阻色谱法评价衣壳和二聚体的浓度。组装的程度随着温度和离子强度的增加而增加。衣壳组装的浓度依赖性符合平衡表达：K-衣壳= [衣壳] /[二聚体]（120）。鉴于HBV衣壳和二聚体的已知几何形状，将每个衣壳组装能量划分为每个亚基-亚基接触的能量。我们可以得出三个主要结论。(i)每个亚基间接触的弱相互作用（从21 ℃低盐下的-2.9 kcal/mol到37 ℃高盐下的-4.4 kcal/mol）导致整体稳定的衣壳;弱亚基间相互作用可能是衣壳呼吸现象的基础。(ii)HBV组装以正焓和正熵为特征。该反应是熵驱动的，与晶体结构中发现的主要疏水接触一致。(iii)增加NaCl浓度增加的自由能，焓和熵的大小，如果离子强度增加的疏水表面埋组装。这最后一点使我们认为，盐的作用是通过诱导二聚体的构象变化，从组装非活性形式到组装活性形式。这种与装配相关的构象变化模型与二聚体和衣壳之间的免疫学差异一致。
Hepatitis B virus (HBV) is an enveloped DNA virus with a spherical capsid (or core). The capsid is constructed from 120 copies of the homodimeric capsid protein arranged with T = 4 icosahedral symmetry. We examined in vitro assembly of purified E. coli expressed HBV capsid protein. After equilibration, concentrations of capsid and dimer were evaluated by size exclusion chromatography. The extent of assembly increased as temperature and ionic strength increased. The concentration dependence of capsid assembly conformed to the equilibrium expression: K-capsid = [capsid] /[dimer](120). Given the known geometry for HBV capsids and dimers, the per capsid assembly energy was partitioned into energy per subunit-subunit contact. We were able to make three major conclusions. (i) Weak interactions (from -2.9 kcal/mol at 21 degreesC in low salt to -4.4 kcal/mol at 37 degreesC in high salt) at each intersubunit contact result in a globally stable capsid; weak intersubunit interactions may be the basis for the phenomenon of capsid breathing. (ii) HBV assembly is characterized by positive enthalpy and entropy. The reaction is entropy-driven, consistent with the largely hydrophobic contacts found in the crystal structure. (iii) Increasing NaCl concentration increases the magnitude of free energy, enthalpy, and entropy, as if ionic strength were increasing the amount of hydrophobic surface buried by assembly. This last point leads us to suggest that salt acts by inducing a conformational change in the dimer from an assembly-inactive form to an assembly-active form. This model of conformational change linked to assembly is consistent with immunological differences between dimer and capsid.