Spectrometers

Solid-state NMR spectra were measured on Bruker spectrometers at ¹H Larmor frequencies of 400 MHz (9.4 Tesla), 600 MHz (14.1 Tesla), and 900 MHz (21.1 Tesla). 4 mm and 3.2 mm MAS probes were used. All ¹³C chemical shifts were referenced externally to the adamantane CH₂ chemical shift at 38.48 ppm on the TMS scale ^{35 (link). 15}N chemical shifts were referenced to the ¹⁵N peak of N-acetylvaline at 122.0 ppm on the liquid ammonia scale ³⁶ . Sample temperatures are thermocouple-reported values.
1D ¹³C and ¹⁵N cross-polarization (CP) spectra were measured under 7–16 kHz MAS at 308 K and 243 K. The high-temperature spectra detect conformational dynamics and proton exchange dynamics, while the low-temperature spectra provide information on the rigid-limit tautomeric structure and protonation state of His37. 1D ¹³C double-quantum (DQ) filtered spectra were measured to suppress the natural-abundance lipid ¹³C signals and give protein-only ¹³C spectra. The SPC5 sequence was used for ¹³C-¹³C dipolar recoupling ³⁷ . The measured dipolar recoupling efficiency was 10–20% at the MAS frequency of 7 kHz. 2D ¹³C-¹³C DARR correlation spectra ³⁸ of VM+ bound M2(21-97) were measured at 600 MHz using mixing times of 30 – 40 ms between 243 K and 249 K. 2D ¹³C-¹³C PDSD spectra of DMPC-bound M2(21–97) were measured at 253 K using a 100 ms mixing time on the 900 MHz spectrometer.

Absorbance data were acquired with an Agilent Cary 60 UV-vis spectrometer. Hydrolysis kinetics were measured with a Tecan Infinite M1000 plate reader. All other fluorescence data were acquired with a PTI QuantaMaster spectrofluorometer. ¹H and ¹³C NMR spectra were acquired on Bruker Spectrometers at the National Magnetic Resonance Facility at Madison (NMRFAM) operating at 500 MHz for ¹H and 125 MHz for ¹³C. Mass spectrometry was performed with a Q Exactive^™ Plus electrospray ionization quadrupole-ion trap (ESI–QIT-MS) mass spectrometer at the Mass Spectrometry Facility in the Department of Chemistry at the University of Wisconsin–Madison. IR spectra were acquired with a Micro FT-IR spectrometer at the Materials Science Center of the University of Wisconsin–Madison. Microscopy images were acquired with a Nikon Eclipse Ti inverted confocal microscope at the Biochemistry Optical Core of the University of Wisconsin–Madison.

¹H (400 and 500 MHz) NMR spectra were recorded using Bruker spectrometers in CDCl₃ and calibrated to the solvent peak of δ 7.26 ppm.