Fig. 3: Characterisation of anti-CgoX mAb D3 epitope.

a S. aureus CgoX structure was modulated from B. subtillis (3I6D.pdb). The linear epitope of mAb D3 (red) was identified by microarray technology using overlapping 13mer CgoX peptides (Supplementary Fig. 3). Protein structure was visualised by EzMol2.1. b Alanine scan of epitope peptides for binding analysis of anti-CgoX mAb D3. Single amino acid positions of the D3 epitope were consecutively replaced by alanine (red in right panel). Immobilised peptides were stained by anti-CgoX mAb D3 detected with anti-mIgG-HRP. Data are presented as mean ± s.d. (n = 2 technical replicates). c Allele frequencies of anti-CgoX mAb D3 epitope. Genome sequences of S. aureus clinical isolates were analysed for epitope aa sequence using the RidomSeqsphere core genome multi locus sequence typing (cgMLST) database. Amino acids interacting with paratope of anti-CgoX mAb D3 according to alanine scan are marked in red. Amino acid differences from identified epitope peptide sequence are marked in blue. Frequencies of alleles with non-restricted binding of anti-CgoX mAb D3 are marked in green. d Uniqueness of the CgoX D3 epitope in S. aureus. Sequence alignment of CgoX from S. aureus with PPOX from H. sapiens and M. musculus. CgoX D3 epitope is depicted in yellow. e Competition analysis of CgoX mAb. Binding of DyLight-649-conjugated anti-CgoX mAb D3 to rCgoX was competed for with different concentrations of unconjugated, indicated mAbs and analysed by ELISA. Binding was determined by fluorescence measurement (Ex 646/Em 674). Data are presented as mean ± s.d. (n = 2). f Saturation binding curve was generated by plotting absorbance signals (OD_450nm) of increasing amounts of anti-CgoX huMAb D3 to rCgoX coated on ELISA MaxiSorp plate using the GraphPadPrism 8.4 software. Kd was calculated by non-linear fitting and the equation for one-site binding model [Y = Bmax*X/(Kd + X)].