Structural Lability of Barley Stripe Mosaic Virus Virions

Virions of Barley stripe mosaic virus (BSMV) were neglected for more than thirty years after their basic properties were determined. In this paper, the physicochemical characteristics of BSMV virions and virion-derived viral capsid protein (CP) were analyzed, namely, the absorption and intrinsic fluorescence spectra, circular dichroism spectra, differential scanning calorimetry curves, and size distributions by dynamic laser light scattering. The structural properties of BSMV virions proved to be intermediate between those of Tobacco mosaic virus (TMV), a well-characterized virus with rigid rod-shaped virions, and flexuous filamentous plant viruses. The BSMV virions were found to be considerably more labile than expected from their rod-like morphology and a distant sequence relation of the BSMV and TMV CPs. The circular dichroism spectra of BSMV CP subunits incorporated into the virions, but not subunits of free CP, demonstrated a significant proportion of beta-structure elements, which were proposed to be localized mostly in the protein regions exposed on the virion outer surface. These beta-structure elements likely formed during virion assembly can comprise the N- and C-terminal protein regions unstructured in the non-virion CP and can mediate inter-subunit interactions. Based on computer-assisted structure modeling, a model for BSMV CP subunit structural fold compliant with the available experimental data was proposed.

大麦条纹花叶病毒（Barley stripe mosaic virus, BSMV）的病毒粒子（virion）在其基本特性被明确后的三十余年间始终未得到足够关注。本文对BSMV病毒粒子及其衍生的病毒衣壳蛋白（capsid protein, CP）的理化特性开展了系统分析，具体涵盖吸收光谱、内源荧光光谱、圆二色谱、差示扫描量热曲线，以及通过动态激光光散射测得的粒径分布。研究结果显示，BSMV病毒粒子的结构特性介于两类经典病毒之间：一类是已被充分表征的刚性杆状病毒粒子烟草花叶病毒（Tobacco mosaic virus, TMV），另一类则为柔丝状植物病毒。相较于其杆状形态以及BSMV与TMV衣壳蛋白间较远的序列相关性，BSMV病毒粒子的稳定性远低于此前预期。针对整合至病毒粒子中的BSMV衣壳蛋白亚基，其圆二色谱呈现出占比可观的β结构元件；而游离状态的衣壳蛋白亚基则无此类特征。研究推测，这类β结构元件主要定位于病毒粒子外表面暴露的蛋白区域，且大概率形成于病毒粒子组装过程中，由非病毒粒子状态衣壳蛋白中未形成结构化结构的N端与C端区域构成，并可介导亚基间的相互作用。基于计算机辅助结构建模，本文提出了一个契合现有实验数据的BSMV衣壳蛋白亚基结构折叠模型。