Calorimetric and dielectrpspectroscopic studies of energy-transfer mechanism of within a protein molecule

利用远缘链球菌的I型葡萄糖转移酶研究了蛋白质分子内的能量传递机制。用差示扫描量热法、介电和圆二色谱对GTF全分子(GTF)、其催化结构域(GS)和葡聚糖结合结构域(DXB)的蛋白质样品进行了研究。差示扫描量热分析结果表明，GTf{ΔH(Gtf)}&lt；ΔH(GS)+ΔH(DXB)的热变性热焓发生了变化。此外，与DXB融合的GS的热变性中温度(Tm)(在GTF内)低于未融合的GS，而DXB与GS融合的Tm(在GTF内)高于未融合的DXB。这些结果表明，GS和DXB的融合可能使前者不稳定，而使后者稳定。然而，CD光谱表明，融合并没有影响这两个结构域的二级和高阶结构。根据这一结果，介电显微镜没有显示出伴随结构域融合的任何显著的水化变化。

The I-type of glucosyltransferase of Streptococcus sobrinus was used to study the of energy-transfer mechanism of within a protein molecule. Protein samples of whole GTF molecule(GTF), its catalytic domain (GS) and glucanbinding domain (DXB) were subjected to differential scanning calorimetry and dielectric and CD spectroscopies. DSC results indicated the enthalpy change of thermal denaturation of GTF{ΔH(GTF)} <ΔH(GS)+ ΔH(DXB). In addition, the T_m (mid-temperature of thermal denaturatin) of GS fused with DXB (within GTF) was lower than that of un-fused GS, whereas T_m of DXB fused with GS (within GTF) was higher than that of un-fused DXB. These results indicate that fusion of GS and DXB may destabilize the former and stabilize the latter. However, CD-spectroscopy indicated that the fusion did not affect the secondary and higher-order structures of either domains. In accordance with this result, dielectroscopy did not show any significant hydration change accompanying the domain fusion.