were performed at the University of Utah Mass Spectrometry and Proteomics
Core facility. ESI was done using a Micromass Quattro-II (Waters),
and analysis of spectra was carried out using predicted masses obtained
from Monoisotopic Mass calculator. FT was performed following cleavage
of heterocyclized peptide by chymotrypsin or PatA protease, using
a LTQ FT Ultra Hybrid Mass Spectrometer (Thermo Scientific) and analyzed
both manually using predicted masses from Monoisotopic calculator
and using Mascot from Matrix Science. MALDI-TOF samples were mixed
with 1-cyano-4-hydroxycinnamic acid (10 mg mL–1 in
50:50 water: methanol with 0.1% trifluoroacetic acid) and analyzed
using a Micromass MALDI micro MX (Waters) using an automated targeting
protocol.