The Multifunctional Role of Substrate-Binding Proteins in Heme Uptake and Antimicrobial Resistance


Pathogenic bacteria scavenge essential nutrients including metals, amino acids and peptides to survive within the hostile host environment. Bacteria utilize ATP-binding cassette (ABC) transporters, powered by the energy of ATP hydrolysis, to move substrates across cellular membranes. The substrate-binding protein (SBP) shuttles substrate in the periplasm and directs the substrate specificity of the transport system. The focus of this dissertation is the multifunctional substrate specificity of SBPs at the interface of the host–pathogen interactions that are necessary for nutrient uptake and antimicrobial resistance. Nontypeable Haemophilus influenzae (NTHi) is an opportunistic pathogen and has four Cluster C SBPs, nthiHbpA (heme-binding protein), nthiOppA (oligopeptide-binding protein), nthiSapA (sensitivity to antimicrobial peptides) and NTHI0310 (putative peptide-binding protein). Unlike other SBP families, some members of the Cluster C family recognize two distinctly different substrates, their canonical substrates and heme. As a heme auxotroph, NTHi relies on host hemoproteins as a source of the essential nutrient. The work in this thesis identifies the heme specificity of the NTHi Cluster C SBPs, defines their binding affinities for canonical and heme substrates, and uncovers ligand-specific sites in the binding pocket for canonical substrates and heme. These studies provide insight into the overlapping function of these Cluster C SBPs in heme uptake and the multisubstrate binding of their canonical substrates and heme to maintain virulence in the host environment.

Alternate Identifier
Date created
Resource type
Rights statement