Spectra were acquired in a Bruker Avance III 800 spectrometer. Data were processed using the software Topspin- (v.2.0) (Bruker BioSpin GmbH, Germany). Assignment was carried out using the interactive program SPARKY (v.3.106) (T.D. Goddard and D.G. Kneller, University of California, San Francisco). GSK458 datasheet Assignment of NOESY spectra and structure calculation was made iteratively using the program ARIA 1.2 [21] and [29] with CNS 1.1 [4]. Initially, the chemical shift index (CSI) was calculated [41] from the Hα chemical shifts assigned. Structure calculations were performed by ARIA and CNS automatically based
on distance restraints derived from homo-nuclear NOESY spectra and from phi and psi-dihedral angles as well as ambiguous hydrogen bonds restraints, characteristic of secondary structure generated by analysis of the chemical shift index. Conversion Galunisertib of CSI output in dihedral restraints was done as implemented in ARIA: −65 and −35 with error estimates of 30° were set respectively as phi and psi dihedral restraints for residues found to be in helical regions from their characteristic Hα chemical shifts [34]. In the last ARIA iteration 200 structures were calculated by restrained simulated annealing and the 20 best structures regarding total energy were refined in an explicit water-box and considered as characteristic
of the ensemble. Midgut homogenates were pre-purified in a 10-kDa filter and the resulting filtrate was submitted to RP-HPLC in a semi-preparative C18 column. Chromatographic fractions were manually collected and tested against C. albicans in a liquid antimicrobial assay. Antimicrobial activity was detected in three fractions that eluted with 32%, 42% and 46% ACN, which were designated I, II and III, respectively ( Fig. 1A), and were further analyzed
by ES-MS. Fraction I revealed to be a mixture of peptides with 1532, 1876 and 2297 Da, whereas fractions II and III contained proteins with molecular masses corresponding to bovine hemoglobin alpha and beta subunits, respectively. The identity of these hemoglobin chains was later confirmed by LC–MS/MS (data not shown). The peptides present in IMP dehydrogenase fraction I were further purified in a second RP-HPLC step in an analytical C18 column. Antimicrobial activity was detected in several fractions, which eluted from 31% to 36% of ACN (Fig. 1B), and these fractions were submitted to ES-MS analysis. A single peptide was detected, eluting at 32% ACN (Fig. 1B, arrow) with a molecular mass of 1876 Da (Fig. 1B, insert). This peptide was present in all fractions with antimicrobial activity and therefore was considered to be the source of this activity. After sequencing by LC–MS/MS, the 1876-Da peptide showed 100% identity with the amino acids 98–114 from the alpha subunit of bovine hemoglobin (Table 1). This 17-amino acid peptide has a theoretical isoelectric point (pI) of 8.8 and is predominantly composed of hydrophobic amino acids (59%).