Analysis of a hybrid TATA box binding protein originating from mesophilic and thermophilic donor organisms

Abstract

The TATA Box Binding Protein (TBP) is a 20 kD protein that is essential and universally conserved in eucarya and archaea. Especially among archaea, organisms can be found that live below 0°C as well as organisms that grow above 100°C. The archaeal TBPs show a high sequence identity and a similar structure consisting of α-helices andβ-sheets that are arranged in a saddle-shape 2-symmetric fold. In previous studies, we have characterized the thermal stability of thermophilic and mesophilic archaeal TBPs by infrared spectroscopy and showed the correlation between the transition temperature (Tm) and the optimal growth temperature (OGT) of the respective donor organism. In this study, a “new” mutant TBP has been constructed, produced, purified and analyzed for a deeper understanding of the molecular mechanisms of thermoadaptation. Theβ-sheet part of the mutant consists of the TBP fromMethanothermobacter thermoautotrophicus(OGT 65°C, MtTBP65) whose α-helices have been exchanged by those ofMethanosarcina mazei(OGT 37°C, MmTBP37). The Hybrid-TBP irreversibly aggregates after thermal unfolding just like MmTBP37 and MtTBP65, but theTm lies between that of MmTBP37 and MtTBP65 indicating that the interaction between the α-helical andβ-sheet part of the TBP is crucial for the thermal stability. The temperature stability is probably encoded in the variable α-helices that interact with the highly conserved and DNA bindingβ-sheets.