Molecular Basis for the Evolution of Species-Specific Hemoglobin Capture by Staphylococcus aureus

Jacob E Choby,Eric P Skaar,Matthew F Barber,Allison J Farrand,Hanna B Buechi,Kimberly A Kline

doi:10.1128/mbio.01524-18

Jacob E Choby, Eric P Skaar + Show 4 more

Open Access

https://doi.org/10.1128/mbio.01524-18

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Abstract

Metals are a limiting resource for pathogenic bacteria and must be scavenged from host proteins. Hemoglobin provides the most abundant source of iron in the human body and is required by several pathogens to cause invasive disease. However, the consequences of hemoglobin evolution for bacterial nutrient acquisition remain unclear. Here we show that the α- and β-globin genes exhibit strikingly parallel signatures of adaptive evolution across simian primates. Rapidly evolving sites in hemoglobin correspond to binding interfaces of IsdB, a bacterial hemoglobin receptor harbored by pathogenic Staphylococcus aureus Using an evolution-guided experimental approach, we demonstrate that the divergence between primates and staphylococcal isolates governs hemoglobin recognition and bacterial growth. The reintroduction of putative adaptive mutations in α- or β-globin proteins was sufficient to impair S. aureus binding, providing a mechanism for the evolution of disease resistance. These findings suggest that bacterial hemoprotein capture has driven repeated evolutionary conflicts with hemoglobin during primate descent.IMPORTANCE During infection, bacteria must steal metals, including iron, from the host tissue. Therefore, pathogenic bacteria have evolved metal acquisition systems to overcome the elaborate processes mammals use to withhold metal from pathogens. Staphylococcus aureus uses IsdB, a hemoglobin receptor, to thieve iron-containing heme from hemoglobin within human blood. We find evidence that primate hemoglobin has undergone rapid evolution at protein surfaces contacted by IsdB. Additionally, variation in the hemoglobin sequences among primates, or variation in IsdB of related staphylococci, reduces bacterial hemoglobin capture. Together, these data suggest that S. aureus has evolved to recognize human hemoglobin in the face of rapid evolution at the IsdB binding interface, consistent with repeated evolutionary conflicts in the battle for iron during host-pathogen interactions.

Highlights

Metals are a limiting resource for pathogenic bacteria and must be scavenged from host proteins
Consistent with the adaptation of S. aureus to colonize and infect humans, we previously found that S. aureus IsdB binds human hemoglobin more effectively than mouse hemoglobin, the common laboratory animal used to model S. aureus infection [13]
These results suggest that hemoglobin variation among mammals dictates effective heme acquisition by S. aureus and other Gram-positive bacteria

Summary

Introduction

Metals are a limiting resource for pathogenic bacteria and must be scavenged from host proteins. The reintroduction of putative adaptive mutations in ␣- or ␤-globin proteins was sufficient to impair S. aureus binding, providing a mechanism for the evolution of disease resistance. These findings suggest that bacterial hemoprotein capture has driven repeated evolutionary conflicts with hemoglobin during primate descent. Variation in the hemoglobin sequences among primates, or variation in IsdB of related staphylococci, reduces bacterial hemoglobin capture Together, these data suggest that S. aureus has evolved to recognize human hemoglobin in the face of rapid evolution at the IsdB binding interface, consistent with repeated evolutionary conflicts in the battle for iron during host-pathogen interactions. The Isd system of S. aureus in part consists of cell wall-anchored IsdB and IsdH, which bind hemoglobin and haptoglobinhemoglobin, respectively [9, 10]

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