Cross-saturation Takahashi et al(2000)Nat.Struc.Biol.7220-223 Protein Proteir Strong binding case 1 NH -CH cross-saturation etoe2laosmcean子ame23taionsapdyansendbyspndmsonoe Cross-saturation to theNHin the Measure peak vstime of saturation tofind residues in more quickly. 言06 N9 04 Chemical shift Cross-saturatior H0215AN 0.2 ppmCross-saturation Takahashi et al (2000) Nat. Struc. Biol. 7 220-223 -NH -CH -15NH -C2H Protein 2 Protein 1 R.F. Band-selective proton saturation, followed by TROSY￾HSQC Saturate the aliphatics of protein 2 - magnetization is rapidly transferred by spin diffusion to the rest of protein 2 i.e. aromatics and amides. Cross-saturation to the 15NH in the interface on protein 1 Measure peak intensity vs time of saturation to find residues in interface Strong binding case cross-saturation Plot intensity ratio vs saturation time. Residues in the interface get saturated more quickly. X-ray structure - buried residues Chemical shift perturbation (#HN2 + 0.15#N2)1/2 > 0.2 ppm H/D exchange protection factor > 10 Cross-saturation (red> light blue > yellow > green > dark blue)