Thermus thermophilus無機ピロリン酸加水分解酵素のThr138の四次構造形成と耐熱性への寄与 Threonine 138 is crucial for the Quaternary Structure and the Thermostability of Thermus thermophilus Inorganic Pyrophosphatase
Inorganic pyrophosphatase (EC. 18.104.22.168) from Thermus thermophilus (Tth PPase) forms the thermostablehexamer，and it was suggested from X-ray studies that its intersubunit interactions stabilize the whole molecule.However，the contribution of Thr138 at the intertrimer interface to quatemary structure and thermostability wasunknown functionally. Therefore，we prepared four Thr138-substituted variants (T138A，V ，N ，and H) bysite-directed mutagenesis. Then，thermostabilities of the enzyme activity and the quatemary structure for T138Vand A were decreased relative to those of the wild type Tth PPase，whereas T138H and N variants remainedmuch hexamer contents and the enzyme activity than T138V and A. Therefore，we suggest that the polar groupin Thr138 of Tth PPase is more crucial than the methyl group for thermostability and quatemary structure，and itmay contribute to the formation of stable trimer-trimer interface.
徳島大学総合科学部自然科学研究 22, 65-73, 2008-12