Taka Junichiro, Ogasahara Kyoko, Jeyakanthan Jeyaraman, Kunishima Naoki, Kuroishi Chizu, Sugahara Mitsuaki, Yokoyama Shigeyuki, Yutani Katsuhide
RIKEN Harima Institute at SPring8, 1-1-1 Kohto, Mikazukicho, Sayo, Hyogo 679-5148.
J Biochem. 2005 May;137(5):569-78. doi: 10.1093/jb/mvi075.
The crystal structure of phosphoribosyl anthranilate isomerase (PRAI) from Thermus thermophilus HB8 (TtPRAI) was solved at 2.0 A resolution. The overall structure of TtPRAI with a dimeric structure was quite similar to that of PRAI from Thermotoga maritima (TmPRAI). In order to elucidate the stabilization mechanism of TtPRAI, its physicochemical properties were examined using DSC, CD, and analytical centrifugation at various pHs in relation to the association-dissociation of the subunits. Based on the experimental results for TtPRAI and the structural information on TtPRAI and TmPRAI, we found that: (i) the denaturation of TtPRAI at acidic pH is correlated with the dissociation of its dimeric form; (ii) the hydrophobic interaction of TtPRAI in the monomer structure is slightly greater than that of TmPRAI, but dimer interface of the TmPRAI is remarkably greater; (iii) the contributions of hydrogen bonds and ion bonds to the stability are similar to each other; and (iv) destabilization due to the presence of cavities in TtPRAI is greater than that of TmPRAI in both the monomer and dimer structures.
嗜热栖热菌HB8（TtPRAI）的磷酸核糖邻氨基苯甲酸异构酶的晶体结构在2.0埃分辨率下得到解析。具有二聚体结构的TtPRAI的整体结构与海栖热袍菌（TmPRAI）的PRAI非常相似。为了阐明TtPRAI的稳定机制，我们在不同pH值下使用差示扫描量热法（DSC）、圆二色光谱法（CD）和分析离心法，结合亚基的缔合-解离，研究了其物理化学性质。基于TtPRAI的实验结果以及TtPRAI和TmPRAI的结构信息，我们发现：（i）TtPRAI在酸性pH下的变性与其二聚体形式的解离相关；（ii）TtPRAI单体结构中的疏水相互作用略大于TmPRAI，但TmPRAI的二聚体界面显著更大；（iii）氢键和离子键对稳定性的贡献彼此相似；（iv）在单体和二聚体结构中，TtPRAI中由于存在空洞而导致的不稳定作用都大于TmPRAI。
