Conjuring up a ghost: structural and functional characterization of FhuF, a ferric siderophore reductase from E. coli.

Iron is a fundamental element for virtually all forms of life. Despite its abundance, its bioavailability is limited, and thus, microbes developed siderophores, small molecules, which are synthesized inside the cell and then released outside for iron scavenging. Once inside the cell, iron removal does not occur spontaneously, instead this process is mediated by siderophore-interacting proteins (SIP) and/or by ferric-siderophore reductases (FSR). In the past two decades, representatives of the SIP subfamily have been structurally and biochemically characterized; however, the same was not achieved for the FSR subfamily. Here, we initiate the structural and functional characterization of FhuF, the first and only FSR ever isolated. FhuF is a globular monomeric protein mainly composed by α-helices sheltering internal cavities in a fold resembling the "palm" domain found in siderophore biosynthetic enzymes. Paramagnetic NMR spectroscopy revealed that the core of the cluster has electronic properties in line with those of previously characterized 2Fe-2S ferredoxins and differences appear to be confined to the coordination of Fe(III) in the reduced protein. In particular, the two cysteines coordinating this iron appear to have substantially different bond strengths. In similarity with the proteins from the SIP subfamily, FhuF binds both the iron-loaded and the apo forms of ferrichrome in the micromolar range and cyclic voltammetry reveals the presence of redox-Bohr effect, which broadens the range of ferric-siderophore substrates that can be thermodynamically accessible for reduction. This study suggests that despite the structural differences between FSR and SIP proteins, mechanistic similarities exist between the two classes of proteins.

Assisted lipid deposition by reductive electrochemical aryldiazonium grafting and insertion of the antiport NhaA protein in this stable biomimetic membrane.

Quartz crystal microbalance studies have been carried out to monitor the fusion of lipid vesicles (pure 1,2-dimyristoyl-sn-glycero-3-phosphocholine, DMPC) and mixed vesicles (DMPC and 4-decylaniline). In order to increase the stability of the lipid deposits onto the electrodes, we have developed an original approach involving electrografting of adsorbed mixed vesicles. Aryldiazonium salts generated in situ from 4-decylaniline (4DA) present in adsorbed and fused mixed vesicles at the electrode surface allow their cathodic reduction and subsequent grafting. The stability of the supported lipid deposit has been shown to significantly increase from less than one day for pure DMPC to about two weeks with the lipid deposition assisted by electrochemical grafting. In this stable lipid deposit, the insertion of the sodium/proton antiporter membrane protein (NhaA) or its inactive mutant has been carried out by fusion of proteoliposomes. This has been followed by characterization of the inserted protein activity by cyclic voltammetry onto an electrode previously modified by an adsorbed pH sensor (2-anthraquinone sulfonate). Activation of the protein function by sodium ions leads to a shift of the interfacial pH and confirms the integrity of the immobilized NhaA.

Unusual long survival despite severe lung disease of a child with biallelic loss of function mutations in ABCA-3.

Homozygous or compound heterozygous for frameshift or nonsense mutations in the ATP-binding cassette transporter A3 (ABCA3) is associated with neonatal respiratory failure and death within the first year of life without lung transplantation. We report the case of a newborn baby girl who developed severe respiratory distress soon after birth. She was diagnosed with compound heterozygous frameshift mutation of the ABCA3 gene. Despite extensive treatment (intravenous corticosteroids pulse therapy, oral corticosteroids, azithromycin, and hydroxychloroquine), she developed chronic respiratory failure. As the parents refused cardio-pulmonary transplantation and couldn't resolve to an accompaniment of end of life, a tracheostomy was performed resulting in continuous mechanical ventilation. A neurodevelopmental delay and an overall muscular dystrophy were noted. At the age of 5 years, after 2 episodes of pneumothorax, the patient died from severe respiratory failure. To our knowledge, this was the first case of a child with compound heterozygous frameshift mutation who posed such an ethical dilemma with a patient surviving till the age of five years.

[Severe hypernatremia due to sea water ingestion in a child]. / Hypernatrémie majeure par intoxication à l'eau de mer chez un enfant.

Drowning in sea water is an unusual cause of severe hypernatremia. We report the case of a 3.5-year-old boy who died 11h after drowning in sea water, with a serum sodium level of 178 mmoL/L. In this case, hypernatremia was aggravated by diarrhea and hyperglycemia with glycosuria. Usually, correction of acute hypernatremia must be quick and early, aiming at a reduction of serum sodium concentration of up to 1-2 mmoL per liter per hour.