The structure of the neisserial lipooligosaccharide phosphoethanolamine transferase A (LptA) required for resistance to polymyxin

Gram-negative bacteria possess an outer membrane envelope consisting of an outer leaflet of lipopolysaccharides, also called endotoxins, which protect the pathogen from antimicrobial peptides and have multifaceted roles in virulence. Lipopolysaccharide consists of a glycan moiety attached to lipid A, embedded in the outer membrane. Modification of the lipid A headgroups by phosphoethanolamine (PEA) or 4-amino-arabinose residues increases resistance to the cationic cyclic polypeptide antibiotic, polymyxin. Lipid A PEA transferases are members of the YhjW/YjdB/YijP superfamily and usually consist of a transmembrane domain anchoring the enzyme to the periplasmic face of the cytoplasmic membrane attached to a soluble catalytic domain. The crystal structure of the soluble domain of the protein of the lipid A PEA transferase from Neisseria meningitidis has been determined crystallographically and refined to 1.4Å resolution. The structure reveals a core hydrolase fold similar to that of alkaline phosphatase. Loop regions in the structure differ, presumably to enable interaction with the membrane-localized substrates and to provide substrate specificity. A phosphorylated form of the putative nucleophile, Thr280, is observed. Metal ions present in the active site are coordinated to Thr280 and to residues conserved among the family of transferases. The structure reveals the protein components needed for the transferase chemistry; however, substrate-binding regions are not evident and are likely to reside in the transmembrane domain of the protein.

Fifteen years single center experience in the management of progressive familial intrahepatic cholestasis of infancy

Recent advances in genetics and in physiopathology of bile composition and excretion have clarified the understanding of progressive familial intrahepatic cholestasis (PFIC). The aim of the present study is to review the experience of our center in terms of diagnosis, management and outcome of 49 pediatric PFIC patients, belonging to the three classical subtypes described. We analyse the clinical, biological, and histological patterns and review the response to the medical and surgical treatment and the global outcome. The only clinical difference between the different subtypes of PFIC patients was the intensity of pruritus. Serum gamma-glutamyltransferase (GGT) and liver histology allowed to differentiate PFIC III from PFIC I and II patients. High levels of biliary bile acids in 2 low-GGT patients was associated with favourable outcome. Response to ursodeoxycholic acid (UDCA) varies from patient to patient and was not associated to a particular subtype of PFIC. In five patients of this cohort, external biliary diversion was performed without improvement. Transplantation is indicated whenever medical treatment fails to restore normal social life, growth and well being of the child and it is associated with excellent survival (> 90%).