This composite part consists of two sessions, the promoter and BBa_K1456006 (designed by Mustafa Semih Elitok iGEM14_ATOMS-Turkiye). The promoter HucR is a bacterial transcriptional repressor. It will dissociate from the binding site hucO8 in the presence of uric acid thus allow the expression of BBa_K1456006, Aprotinin.
How does it work?
The promoter is designed to be sensitive to the concentration of uric acid. This promoter controls the expression of Aprotinin that is downstream the promoter. The promoter session consists of a constitutive promoter J23100, a RBS B0034, a strong repressor KRAB-HucR and a double terminator B0015. HucR is in itself a repressor. Its repressing ability is enhanced by KRAB. The resulting repressor is a chimeric mammalian urate-dependent transsilencer (mUTS). hucO is an operative site for mUTS to bind to. When mUTS is binded to hucO, the expression of downstream gene is restricted according to the concentration of substrates. The presence of uric acid limits the binding of mUTS to hucO. The limitation varies with the concentration of uric acid. Downstream of the promoter session is a constitutive promoter J23106, a RBS B0034, a gene K1456006 and a double terminator B0015. As a result mUTS binds to hucO and GFP is not expressed when uric acid is absent or at very low concentration. Alternatively, the complex detaches from hucO and GFP is expressed according to the concentration of uric acid. The promoter controls the expression of aprotinin.
As Xanthine Oxidase (XO) is an enzyme catalysing the oxidation of hypoxanthine to xanthine. It can actually further catalyze the oxidation of xanthine to uric acid. Aprotinin is a potent protease inhibitor which prevents the formation of xanthine oxidase (XO) from xanthine dehydrogenase (XDH). Therefore according to this theory, when there are higher uric acid levels in blood, more aprotinin will be expressed and less xanthine or uric acid will be produced by oxidation.