1H NMR (300 MHz or 400 MHz), 13C NMR (75 MHz, 100 MHz) were conducted on a Bruker spectrometer at 25 °C and were calibrated using residual undeuterated solvent as an internal reference. Chemical shifts were reported in ppm and coupling constants (J) were quoted to the nearest 0.1 Hz. High resolution mass spectrometry (HRMS) was recorded using a Bruker maXis II High Resolution QTOF. Peptides were analyzed by LC-MS with an Agilent 1260 Infinity HPLC system connected to a Thermo Finnigan LCQ DecaXP MS detector. Peptides were further purified by a preparative HPLC system with Waters 2535 Quaternary Gradient Module, Waters 515 HPLC pump, Waters SFO System Fluidics Organizer and Waters 2767 Sample Manager.
Photo-cross-linking were performed with ENF-260C/FE hand-hang UV lamp (Spectroline). In-gel fluorescence scanning was performed using a Typhoon 9410 variable mode imager from GE Healthcare Life Sciences (excitation 532 nm, emission 580 nm). All images were processed by ImageJ software (National Institutes of Health), and contrast was adjusted appropriately.