Differential Function of Lip Residues in the Mechanism and Biology of an Anthrax Hemophore

PLoS Pathogens

John S. Olson¹  Marian Fabian¹  Catherine B. Poor²  Chuan He²  Erol Balkabasi³  Erin S. Honsa³  MarCia T. Ekworomadu³  Miriam A. Balderas³  Anthony W. Maresso³  Cedric P. Owens⁴  Celia W. Goulding⁴  Frank Murphy⁵ 

[1] Department of Biochemistry and Cell Biology, Rice University, Houston, Texas, United States of America;Department of Chemistry, University of Chicago, Chicago, Illinois, United States of America;Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas, United States of America;Departments of Molecular Biology and Biochemistry, University of California-Irvine, Irvine, California, United States of America;Northeastern Collaborative Access Team, Argonne National Laboratory, Argonne, Illinois, United States of America

关键词: Heme;    Hemoglobin;    Bacillus anthracis;    Crystal structure;    Bacterial pathogens;    Gram positive bacteria;    Protein structure;    Chemical dissociation;   

DOI  :  10.1371/journal.ppat.1002559

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

To replicate in mammalian hosts, bacterial pathogens must acquire iron. The majority of iron is coordinated to the protoporphyrin ring of heme, which is further bound to hemoglobin. Pathogenic bacteria utilize secreted hemophores to acquire heme from heme sources such as hemoglobin. Bacillus anthracis, the causative agent of anthrax disease, secretes two hemophores, IsdX1 and IsdX2, to acquire heme from host hemoglobin and enhance bacterial replication in iron-starved environments. Both proteins contain NEAr-iron Transporter (NEAT) domains, a conserved protein module that functions in heme acquisition in Gram-positive pathogens. Here, we report the structure of IsdX1, the first of a Gram-positive hemophore, with and without bound heme. Overall, IsdX1 forms an immunoglobin-like fold that contains, similar to other NEAT proteins, a 310-helix near the heme-binding site. Because the mechanistic function of this helix in NEAT proteins is not yet defined, we focused on the contribution of this region to hemophore and NEAT protein activity, both biochemically and biologically in cultured cells. Site-directed mutagenesis of amino acids in and adjacent to the helix identified residues important for heme and hemoglobin association, with some mutations affecting both properties and other mutations affecting only heme stabilization. IsdX1 with mutations that reduced the ability to associate with hemoglobin and bind heme failed to restore the growth of a hemophore-deficient strain of B. anthracis on hemoglobin as the sole iron source. These data indicate that not only is the 310-helix important for NEAT protein biology, but also that the processes of hemoglobin and heme binding can be both separate as well as coupled, the latter function being necessary for maximal heme-scavenging activity. These studies enhance our understanding of NEAT domain and hemophore function and set the stage for structure-based inhibitor design to block NEAT domain interaction with upstream ligands.

【 授权许可】

CC BY