Ligand-gated membrane channels selectively facilitate the entry of iron into prokaryotic cells. The essential role of iron in metabolism makes its acquisition a determinant of bacterial pathogenesis and a target for therapeutic strategies. In Gram-negative bacteria, TonB-dependent outer membrane proteins form energized, gated pores that bind iron chelates (siderophores) and internalize them. The time-resolved operation of the Escherichia coli ferric enterobactin receptor FepA was observed in vivo with electron spin resonance spectroscopy by monitoring the mobility of covalently bound nitroxide spin labels. A ligand-binding surface loop of FepA, which normally closes its transmembrane channel, exhibited energy-dependent structural changes during iron and toxin (colicin) transport. These changes were not merely associated with ligand binding, but occurred during ligand uptake through the outer membrane bilayer. The results demonstrate by a physical method that gated-porin channels open and close during membrane transport in vivo.

Siderophores and colicins enter bacterial cells through TonB-dependent outer membrane proteins. Using site-directed substitution mutagenesis, we studied ligand recognition by a prototypic Escherichia coli siderophore receptor, FepA, that binds the iron chelate ferric enterobactin and colicins B and D. These genetic experiments identified a common binding site for two of the three ligands, containing multiple positive charges, within cell surface residues of FepA. Elimination of single residues in this region did not impair the adsorption or transport of ferric enterobactin, but double mutagenesis in the charge cluster identified amino acids (Arg-286 and Arg-316) that participate in siderophore binding and function in FepA-mediated killing by colicins B and D. Ferric enterobactin binding, furthermore, prevented covalent modification of FepA within this domain by either a f luorescent probe or an arginine-specific reagent, corroborating the involvement of this site in ligand recognition. These results identify, for the first time, residues in a TonB-dependent outer membrane protein that participate in ligand binding. They also explain the competition between ferric enterobactin and the colicins on the bacterial cell surface: all three ligands interact with the same arginine residues within FepA during their penetration through the outer membrane.

The Escherichia coli FepA protein is an energy-and TonB-dependent, ligand-binding porin that functions as a receptor for the siderophore ferric enterobactin and colicins B and D. We characterized the kinetic and thermodynamic parameters associated with the initial, energy-independent steps in ligand binding to FepA.

BACKGROUND-Immunoreconstitution of HIV-infected (HIV+) patients after treatment with highly antiretroviral therapy (HAART) appears to provoke inflammatory diseases.

The incidence of asthma and atopic dermatitis (AD) were evaluated in HIV-infected (n=451) compared to HIV-exposed (n=227) but uninfected (HEU) children and adolescents by abstraction from clinical charts. Asthma was more common in HIV-infected compared to HEU children by clinical diagnosis (25% vs. 20%, p = 0.101), by asthma medication use, (31% vs. 22%, p = 0.012), and by clinical diagnosis or both medication use, (34% vs. 25%, p = 0.012). HIV-infected children had a greater risk of asthma compared to HEU children (HR = 1.37, 95% CI: 1.01 to 1.86). AD was more common in HIV-infected than HEU children (20% vs. 12%, p = 0.009)) and children with AD were more likely to have asthma in both cohorts (41% vs. 29%, p = 0.010). HIV-infected children and adolescents in this study had a 30% increased incidence of asthma and AD, a finding critical for millions of HIV-infected children worldwide.

Youth infected with HIV at birth often have sleep disturbances, neurocognitive deficits, and abnormal psychosocial function which are associated with and possibly resulted from elevated blood cytokine levels that may lead to a decreased quality of life. To identify molecular pathways that might be associated with these disorders, we evaluated 38 HIV-infected and 35 uninfected subjects over 18-months for intracellular cytokine levels, sleep patterns and duration of sleep, and neurodevelopmental abilities. HIV infection was significantly associated with alterations of intracellular pro-inflammatory cytokines (TNF-α, IFN-γ, IL-12), sleep factors (total time asleep and daytime sleep patterns), and neurocognitive factors (parent and patient reported problems with socio-emotional, behavioral, and executive functions; working memory-mental fatigue; verbal memory; and sustained concentration and vigilance. By better defining the relationships between HIV infection, sleep disturbances, and poor psychosocial behavior and neurocognition, it may be possible to provide targeted pharmacologic and procedural interventions to improve these debilitating conditions.

Background The effect of pre-transplant conditioning upon the long-term outcomes of patients receiving hematopoietic stem cell transplantation (HSCT) for severe combined immunodeficiency (SCID) has not been completely determined. Objective To assess the outcomes of 23 mostly conditioned SCID patients and compare their outcomes to 25 nonconditioned SCID transplanted patients previously reported. Methods In the present study, we reviewed the medical records of these 23 consecutive mostly conditioned SCID patients transplanted between 1998 and 2007. Results Eighteen patients (median age at transplant 10 [range 0.8–108] mo) received haploidentical mismatched related donor, matched unrelated donor, or mismatched unrelated donor transplants, 17 of whom received pretransplant conditioning and one was not conditioned, 13 (72%) engrafted and survive a median of 3.8 [1.8–9.8] yr, 5 of 13 (38%) require IVIG, and 6 of 6 age-eligible children attend school. Of five recipients (median age at transplant 7 [range 2–23] mo) of matched related donor transplants, all 5 engrafted and survive a median of 7.5 [range 1.5–9.5] yr, 1 requires IVIG, and 3 of 3 age-eligible children attend school. Gene mutations were known in 16 cases: IL2γR in 7 patients, IL7αR in 4 patients, RAG1 in 2 patients, ADA in 2 patients, and AK2 in 1 patient. Early outcomes and quality of life of the previous non-conditioned vs. the present conditioned cohorts were not statistically different but longer-term follow-up is necessary for confirmation. Conclusions HSCT in SCID patients results in engraftment, long-term survival, and a good quality of life for the majority of patients with or without pre-transplant conditioning.

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