Research Paper Volume 8, Issue 12 pp 3419—3429

Figure 2. Sensorgrams of binding kinetics of immobilized QSOX to various PrP proteins. Surface Plasmon Resonance (SPR) was applied as a label-free detection method to determine the binding kinetics of QSOX with various domains of PrPs. The results reveal that the equilibrium constant (KD) is relatively low for the C-terminal globular region of human or mouse PrP (472 or 312 nM) comparing to the unfolded N-terminal region of HuPrP23-145 (3.6 nM). QSOX exhibits a higher affinity for the unstructured N-terminal region than for the C-terminal folded region of PrP, suggesting that the unfolded N-terminal region of PrP is a substrate for QSOX. Interestingly, the octamer form of moPrP89-230 displays high affinity toward QSOX (1.7 nM), indicating that a misfolded form of PrP is a potential substrate for QSOX, in agreement with our in vitro study showing that QSOX binds to PrP^Sc from prion-infected human and animal brains. MoPrP23-230 was injected on immobilized QSOX (A), Octamer (B), MoPrP89-230 (C), HuPrP23-231 (D), HuPrP90-231 (E), HuPrP23-145 (F). Sensorgrams showing the evolution of response (RU, resonance units) using CM5 sensor chip performed in BIAcore 3000 instrument.