Unusual Stability of Anabaena Sensory Rhodopsin Transducer from Anabaena PCC7120.

Advances in biotechnology generated wide range of microbial genome and their related protein database. Freshwater cyanobacterium Anabaena PCC7120 sensory rhodopsin, ASR in contrast to classical haloarchaeal sensory rhodopsins interacts with putative soluble transducer, ASRT. The 125 amino acid transducer exists as a soluble protein and is involved in photoreceptor binding. Recombinant DNA tools in biotechnology conventionally support the use of affinity tags for ease of protein purification and subsequent studies. The ASRT exists as a stable tetramer. Both X-ray crystal structure and solution NMR results with ASRT utilizing hexa-histidine affinity tag reveal it as a primarily β-stranded protein We have observed that the affinity tagged ASRT exhibits altered oligomeric stability. In this communication we outlined the effect of commonly used denaturant, Sodium Dodecyl Sulfate (SDS) on the tetrameric packing of ASRT. Our results support that N-terminus hexa-histidine tagged ASRT displayed unusual SDS-resistant structure. The unusual stability of ASRT and its homologues present in other microbial population could provide further insight towards their role in receptor, other ligand binding and signaling.