Wintrode P L, Griko Y V, Privalov P L
Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Protein Sci. 1995 Aug;4(8):1528-34. doi: 10.1002/pro.5560040810.
The energetics of barstar denaturation have been studied by CD and scanning microcalorimetry in an extended range of pH and salt concentration. It was shown that, upon increasing temperature, barstar undergoes a transition to the denatured state that is well approximated by a two-state transition in solutions of high ionic strength. This transition is accompanied by significant heat absorption and an increase in heat capacity. The denaturational heat capacity increment at approximately 75 degrees C was found to be 5.6 +/- 0.3 kJ K-1 mol-1. In all cases, the value of the measured enthalpy of denaturation was notably lower than those observed for other small globular proteins. In order to explain this observation, the relative contributions of hydration and the disruption of internal interactions to the total enthalpy and entropy of unfolding were calculated. The enthalpy and entropy of hydration were found to be in good agreement with those calculated for other proteins, but the enthalpy and entropy of breaking internal interactions were found to be among the lowest for all globular proteins that have been studied. Additionally, the partial specific heat capacity of barstar in the native state was found to be 0.37 +/- 0.03 cal K-1 g-1, which is higher than what is observed for most globular proteins and suggests significant flexibility in the native state. It is known from structural data that barstar undergoes a conformational change upon binding to its natural substrate barnase.(ABSTRACT TRUNCATED AT 250 WORDS)
通过圆二色光谱（CD）和扫描量热法，在较宽的pH值和盐浓度范围内研究了巴司星（barstar）的变性能量学。结果表明，随着温度升高，在高离子强度溶液中，巴司星向变性状态的转变很好地符合两态转变。这种转变伴随着大量的热吸收和热容增加。发现在约75℃时变性热容增量为5.6±0.3kJ K⁻¹ mol⁻¹。在所有情况下，测得的变性焓值明显低于其他小的球状蛋白。为了解释这一现象，计算了水合作用和内部相互作用破坏对总展开焓和熵的相对贡献。发现水合焓和熵与其他蛋白质计算值吻合良好，但内部相互作用断裂的焓和熵在所有已研究的球状蛋白中是最低的。此外，发现天然状态下巴司星的偏比热容量为0.37±0.03 cal K⁻¹ g⁻¹，高于大多数球状蛋白，表明其天然状态具有显著的灵活性。从结构数据可知，巴司星与天然底物巴纳酶（barnase）结合时会发生构象变化。（摘要截短于250字）
