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

Mutagenesis of the N-terminal alpha helix of human α-globin revealed that substituting the Lys of baboon 160 at position 8 significantly reduced binding by S. aureus ( Figure 3D ). Additionally, substituting A5D, T8K, 161 and N9H in human α-globin, which converts this 7 amino acid region to that of baboon, leaves S. aureus 162 binding indistinguishable from that of baboon hemoglobin. These results demonstrate that the N-terminal 163 helix of α-globin makes a major contribution to S. aureus hemoglobin specificity. Next, the relative 164 importance of the rapidly evolving N78 residue in α-globin was assessed, which lies N-terminal to the 165 sixth alpha helix ( Figure 3B ). Substitution of N78 to glutamine (present in baboon, talapoin, and other Old 166 World primates) or to histidine, reduced binding of human hemoglobin ( Figure 3E ). Thus, substitutions at 167 multiple residues in α-globin that exhibit signatures of repeated positive selection disrupt the ability of S. 168 aureus to recognize human hemoglobin. 169 9 170 All rights reserved. No reuse allowed without permission.