Abstract Title
Persistence of Nontypeable Haemophilus influenzae is dependent upon selective import of nutrients and host antimicrobial peptides

Research Category
Infectious Disease / Immunology

Author(s)
Derek Heimlich
Kari Tanaka, Andrew Vogel, Alistair Harrison, Heather Pinkett, and Kevin Mason

Abstract
Nontypeable Haemophilus influenzae (NTHI) responds to host microenvironmental cues, including host-derived antimicrobial peptides (AMPs) and the essential nutrient heme-iron, to mediate pathogenesis. We identified multifunctional roles for the Sap ABC transporter, critical to import heme-iron for nutrition and AMPs for intracellular degradation. The Sap transporter shares a common five subunit architecture with other ABC transporters: a periplasmic substrate binding protein, SapA, two transmembrane permease proteins, SapB and SapC, and two membrane-associated nucleotide-binding proteins, SapD and SapF. Phenotypic analysis of structural mutants suggested that the Sap transporter does not fit the canonical description of other ABC transporter systems. Instead, Sap complex assembly may vary, and as such dictate function. We hypothesized that coordination of protein assembly of the Sap complex dictates selectivity of substrate transport. NTHI mutants deficient in ATPase and permease proteins were assessed for roles in heme-iron utilization and neutralization of AMPs. One ATPase was required for heme-iron utilization but was dispensable for AMP resistance. In contrast, the second ATPase was required for AMP resistance. NTHI strains engineered to produce select permease-ATPase complexes demonstrated differential susceptibility to AMPs, supporting our hypothesis that selective coupling of permease-ATPase proteins dictates substrate import. These studies provide potential for the development of novel therapeutic alternatives to neutralize essential import functions and thereby reduce NTHI persistence during disease.