Spectroscopic analysis on the effect of temperature on Kunitz domain 1 of human tissue factor pathway inhibitor-2

The conformation of Kunitz domain 1 of human tissue factor pathway inhibitor-2 (hTFPI-2/KD1) has been studied by fourier transform infrared spectroscopy, circular dichroism, and Raman spectroscopy. It was found that hTFPI-2/KD1 contained approximately 17% alpha-helices, 24% beta-strands, 46% random coils, 13% beta-turns, and two kinds of disulfide bonds(ggg and tgt) at 25 degrees C. The detailed conformational changes of the heated protein observed by fourier transform infrared spectroscopy, circular dichroism and Raman spectroscopy revealed that hTFPI-2/KD1 was thermally stable. However, KD1 could form an intermediate form at high temperature, then return to its normal conformation when the temperature was lowered. Activity assays also showed that hTFPI-2/KD1 was able to keep its inhibitory activity on plasmin after being heated to 80 degrees C for 5 min.