A study of structural stability of kinase-related protein (KRP)

The structural stability of the smooth muscle kinase-related protein (KRP) was studied by various methods: intrinsic (tryptophanyl) protein fluorescen ce, differential scanning calorimetry, and NMR. It was suggested from the a nalysis of fluorescence and NMR spectra and fluorescence quenching that KRP is a compact globular protein, with neither the carboxy- nor the aminoterm inal high-mobility domains incorporated into the globule. The only tryptoph an residue of the molecule is inside the globule, inaccessible for water mo lecules and poorly accessible for iodide and acrylamide. The lack of fluore scence quenching by Cs+ suggests that positively charged groups are dominan t in the vicinity of the tryptophan residue. Studies of the KRP molecule to lerance to guanidine hydrochloride (GHC), pH, and temperature changes revea led that, in addition to native and unfolded conformational states, there a re intermediate conformational states, which are characterized by high intr amolecular mobility. Transition from native to an intermediate state occurs at moderately low concentrations of GHC (<1.5 M), pH 8-10, and temperature close to physiological (<37 degrees C). The intermediate confrontational s tructures are suggested to contribute to the functional activity of the pro tein.