Atoxin. (C) The re-purification of hemachatoxin on a shallow gradient of 35?5 solvent B. The elution was order BTZ043 monitored at 215 nm. (D) The 1418741-86-2 site ESI-MS profile of hemachatoxin showing the three peaks of mass/charge (m/z) ratio ranging from +4 to +6 charges. The mass of hemachatoxin was determined to be 6835.6860.94 Da. doi:10.1371/journal.pone.0048112.gHemachatoxin from Ringhals Cobra VenomFigure 2. Multiple sequence alignment of hemachatoxin with cardiotoxins/cytotoxins (A) and other three-finger toxins (B). Toxin names, species and accession numbers are shown. Conserved residues in all the sequences are highlighted in black. The type of cardiotoxin based on the conserved Pro31 is highlighted in grey. Disulfide linkages and loop regions are also shown. The sequence identity (in percentage) of each protein with hemachatoxin is shown at the end of each sequence. doi:10.1371/journal.pone.0048112.gdetermined by electrospray ionization mass spectrometry (ESIMS). ESI-MS showed 3 peaks of mass/charge (m/z) ratio ranging from +4 to +6 charges (Figure 1D). The mass was calculated to be 6835.6860.94 Da.Thus hemachatoxin belongs to the 3FTx family based on sequence similarity and the position of cysteine residues (Figure 2).Structural AnalysisThe structure of hemachatoxin was determined by the molecular replacement method using Naja nigricollis toxin-c coordinates (PDB code 1TGX) as a search model. There were two hemachatoxin molecules in an asymmetric unit with each molecule consisting of residues from Leu1 to Asn61 (Figure 3A). Both monomers are well defined in the electron density map (Figure 3B). The model was refined to 
a final R value of 0.23 (Rfree = 0.28) (Table 1). The stereochemical parameters of the model were analyzed by PROCHECK [45] and all residues are in the allowed regions of the Ramachandran plot. Each monomer of the asymmetric unit consists of 6 anti-parallel b-strands (b2Qb1qb4Qb3qb6Qb5q) that form two b-sheets (Figure 3A). The first b-sheet consists of two anti-parallel bstrands, b1 (Lys2-Lys6) and b2 (Phe10-Thr14), while the second contains four anti-parallel strands, b3 (Leu21-Thr26), b4 (Ile35Thr40), b5 (Ala42-Ser47) and b6 (Lys51-Asn56). The fold of hemachatoxin is maintained by four disulfide bonds, 1081537 and these cysteines are strictly conserved among the 3FTxs. The three fingers of hemachatoxin consist of the secondary structures b1Vb2, b3Vb4 and b5Vb6 (Figure 3A). The electrostatic surface representation shows that loops I and II are predominantly charged residues, whereas loop III is highly hydrophobic in nature (Figure 3C). The sequence alignment revealed the conservedSequence Determination and AnalysisWe determined the complete amino acid sequence of hemachatoxin by automated Edman degradation. The first 45 amino acid residues were determined by sequencing the native protein while the remaining sequence was determined from overlapping fragments of chemically-cleaved S-pyridylethylated hemachatoxin (Figure S1A,S1B, S2) (Table S1). The calculated mass of 6836.4 Da from the hemachatoxin sequence agrees well with the experimentally determined molecular mass (6835.6860.94 Da). The crystal structure (see below) with well defined electron density for the entire hemachatoxin molecule was used to confirm the experimentally determined sequence of the protein as described earlier [41]. The BLAST search [42] showed that hemachatoxin is closely related (.70 identity) to cardiotoxins/cytotoxins, a subgroup of 3FTxs (Figure 2A). Hemachatoxin e.Atoxin. (C) The re-purification of hemachatoxin on a shallow gradient of 35?5 solvent B. The elution was monitored at 215 nm. (D) The ESI-MS profile of hemachatoxin showing the three peaks of mass/charge (m/z) ratio ranging from +4 to +6 charges. The mass of hemachatoxin was determined to be 6835.6860.94 Da. doi:10.1371/journal.pone.0048112.gHemachatoxin from Ringhals Cobra VenomFigure 2. Multiple sequence alignment of hemachatoxin with cardiotoxins/cytotoxins (A) and other three-finger toxins (B). Toxin names, species and accession numbers are shown. Conserved residues in all the sequences are highlighted in black. The type of cardiotoxin based on the conserved Pro31 is highlighted in grey. Disulfide linkages and loop regions are also shown. The sequence identity (in percentage) of each protein with hemachatoxin is shown at the end of each sequence. doi:10.1371/journal.pone.0048112.gdetermined by electrospray ionization mass spectrometry (ESIMS). ESI-MS showed 3 peaks of mass/charge (m/z) ratio ranging from +4 to +6 charges 
(Figure 1D). The mass was calculated to be 6835.6860.94 Da.Thus hemachatoxin belongs to the 3FTx family based on sequence similarity and the position of cysteine residues (Figure 2).Structural AnalysisThe structure of hemachatoxin was determined by the molecular replacement method using Naja nigricollis toxin-c coordinates (PDB code 1TGX) as a search model. There were two hemachatoxin molecules in an asymmetric unit with each molecule consisting of residues from Leu1 to Asn61 (Figure 3A). Both monomers are well defined in the electron density map (Figure 3B). The model was refined to a final R value of 0.23 (Rfree = 0.28) (Table 1). The stereochemical parameters of the model were analyzed by PROCHECK [45] and all residues are in the allowed regions of the Ramachandran plot. Each monomer of the asymmetric unit consists of 6 anti-parallel b-strands (b2Qb1qb4Qb3qb6Qb5q) that form two b-sheets (Figure 3A). The first b-sheet consists of two anti-parallel bstrands, b1 (Lys2-Lys6) and b2 (Phe10-Thr14), while the second contains four anti-parallel strands, b3 (Leu21-Thr26), b4 (Ile35Thr40), b5 (Ala42-Ser47) and b6 (Lys51-Asn56). The fold of hemachatoxin is maintained by four disulfide bonds, 1081537 and these cysteines are strictly conserved among the 3FTxs. The three fingers of hemachatoxin consist of the secondary structures b1Vb2, b3Vb4 and b5Vb6 (Figure 3A). The electrostatic surface representation shows that loops I and II are predominantly charged residues, whereas loop III is highly hydrophobic in nature (Figure 3C). The sequence alignment revealed the conservedSequence Determination and AnalysisWe determined the complete amino acid sequence of hemachatoxin by automated Edman degradation. The first 45 amino acid residues were determined by sequencing the native protein while the remaining sequence was determined from overlapping fragments of chemically-cleaved S-pyridylethylated hemachatoxin (Figure S1A,S1B, S2) (Table S1). The calculated mass of 6836.4 Da from the hemachatoxin sequence agrees well with the experimentally determined molecular mass (6835.6860.94 Da). The crystal structure (see below) with well defined electron density for the entire hemachatoxin molecule was used to confirm the experimentally determined sequence of the protein as described earlier [41]. The BLAST search [42] showed that hemachatoxin is closely related (.70 identity) to cardiotoxins/cytotoxins, a subgroup of 3FTxs (Figure 2A). Hemachatoxin e.