Yapısal bilgiyi kullanarak PER-ARNT-SIM (PAS) bölgeleri içeren biyolojik saat proteinlerinin etkileşimlerinin analizi

Per-ARNT- Sim (PAS) domains are modular protein units those are critical for regulation of clock-controlled gene expression. The mammalian BMAL1 and CLOCK are the transcription factors that contain two basic helix-loop-helix domains and bind E-box elements (CACGTG) of clock regulated genes including the Period and Cryptochrome and activate their transcription. Then the PERIOD (PER) and CRYPTOCHROME (CRY) proteins form ternary complexes with casein kinase I? (CKI?) in the cytoplasm and translocate into the nucleus, where they act as a negative regulator of BMAL1/CLOCK-driven transcription. To understand the nature of interaction between PER2-CLOCK-BMAL1 complex, we performed structure based analysis on protein-protein interactions (PPI) those formed via PAS domains of clock proteins. This complex was analyzed by using structural data and efficient structural comparison algorithms to predict potential interactions. Since there are no available atomic structures for our proteins of interest, homology models are used. In our model, BMAL1 and CLOCK interacts with each other through their PAS B domains and the PER2 interacts with this dimer through the PAS B domain of the CLOCK. On BMAL1/CLOCK interface, we found 12 hotspots, 7 residues on BMAL1 (347,349,362,405,427,429,441), 5 residues on CLOCK (317, 338, 350, 352,376). On PER2/CLOCK interface, 8 hotspots are found, 3 residues on PER2 (414, 429,431) and 5 residues on CLOCK (332,354,356,333,361). Here we show how, using structural data and efficient comparison algorithms can explain forming the clock complexes at the molecular level. This study is not only important to understand clock mechanism at structural level but also will allow us to develop drugs against clock-regulated diseases, like Jet-Lag and some forms of depression.