Molecular basis for the evolution of species-specific hemoglobin capture by pathogenic Staphylococcus

Jacob E. Choby; Hanna B. Buechi; Allison J. Farrand; Eric P. Skaar; Matthew F. Barber

The copyright holder for this preprint (which was not peer-reviewed) is the author/funder. . https://doi.org/10.1101/339705 doi: bioRxiv preprint p<0.005; *** p<0.0005 by two-way ANOVA with Sidak correction for multiple comparisons. 179 β-globin divergence contributes to S. aureus hemoglobin binding. 180 S. aureus was capable of binding α-baboon β-human chimeric hemoglobin with higher affinity 181 than baboon hemoglobin ( Figure 3A ), signifying that β-globin also contributes to S. aureus species-182 specific hemoglobin capture. Therefore, the contribution of rapidly evolving residues in β-globin to this 183 binding interaction were investigated ( Figure 4A ). Both S9 and A76 interact closely with the NEAT1 184 domain of IsdB ( Figure 4B ). The effect of substituting human β-globin S9 and A76 with residues found in 185 other primate species analyzed in this work was systematically tested, which revealed that A76 is 186 particularly important for binding by S. aureus ( Figure 4C ). Notably, baboon hemoglobin displays 187 phylogenetic variation at both position 9 and 76, suggesting that these residues may contribute to the 188 inability of IsdB to bind baboon hemoglobin. This variance might also explain the binding affinity 189 differences between human hemoglobin and the α-human β-baboon chimera, observed in Figure 3A . As 190 for α-globin, no single residue substitution improved binding by S. aureus IsdB, consistent with the idea 191 that IsdB has specifically adapted to bind human hemoglobin. Taken together with earlier data, residues 192 at the IsdB interface of both α-globin and β-globin contribute to recognition of hemoglobin by S. aureus. 193 This is consistent with the NEAT1 domain of multiple IsdB monomers engaging in hemoglobin capture 194 by binding both α-and β-globins, as observed in the co-crystal structure (22). 195 All rights reserved. No reuse allowed without permission.