Casadevall A, Day L A
Department of Developmental and Structural Biology, Public Health Research Institute of the City of New York, New York 10016.
Biochemistry. 1988 May 17;27(10):3599-602. doi: 10.1021/bi00410a010.
The circular dichroism (CD) of Pfl filamentous virus has been examined over the temperature range 0-40 degrees C, in the absence and presence of Hg(II), Ag(I), and Cu(II). Thermal difference CD spectra were obtained by subtraction of spectra recorded above and below a thermally induced structure transition near 12 degrees C. The thermal difference spectra look like they arise from shifts in two exciton bands, one centered at 230 nm and the other at 290 nm. The amplitudes on either side of a crossover at 230 nm are 10 times those of a crossover at 290 nm. It is proposed that the difference spectra result from thermally induced shifts in coupled oscillator interactions between Tyr40 residues of the coat protein and the guanine and cytosine bases of the DNA. Metal ions can reduce or block these shifts. The changes in ellipticities at 220, 237, and 270 nm induced by changing the temperature have inflections near 12 degrees C. Ag(I) and Hg(II), which are known to bind to the DNA bases in Pfl, reduce or eliminate the inflections in the thermal profiles, depending on the metal ion type and concentration. Cu(II) ions do not affect the profiles. The spectral changes and the effects of the metal ions indicate intimate contact between the DNA bases and the protein subunits in the virion.
在0至40摄氏度的温度范围内，在不存在和存在Hg(II)、Ag(I)和Cu(II)的情况下，对Pfl丝状病毒的圆二色性（CD）进行了检测。通过减去在接近12摄氏度的热诱导结构转变之上和之下记录的光谱，获得了热差CD光谱。热差光谱看起来像是由两个激子带的位移引起的，一个以230纳米为中心，另一个以290纳米为中心。在230纳米处交叉点两侧的振幅是在290纳米处交叉点振幅的10倍。有人提出，差异光谱是由衣壳蛋白的Tyr40残基与DNA的鸟嘌呤和胞嘧啶碱基之间的耦合振荡器相互作用的热诱导位移引起的。金属离子可以减少或阻止这些位移。通过改变温度在220、237和270纳米处诱导的椭圆率变化在12摄氏度附近有拐点。已知与Pfl中的DNA碱基结合的Ag(I)和Hg(II)，根据金属离子的类型和浓度，会减少或消除热谱中的拐点。Cu(II)离子不影响热谱。光谱变化和金属离子的作用表明病毒粒子中DNA碱基与蛋白质亚基之间存在密切接触。
