Transport of ferric-aerobactin into the periplasm and cytoplasm of Escherichia coli K12: role of envelope-associated proteins and effect of endogenous siderophores.

Purified [14C]aerobactin, supplied exogenously to non-growing bacteria, was translocated via the periplasm into the cytoplasm of Escherichia coli K12 strains expressing the aerobactin receptor protein IutA. No significant uptake was observed into either compartment of strains lacking the iutA gene or specifically defective in tonB. Uptake into both compartments was markedly reduced, but not abolished, in an exb mutant. Accumulation of [14C]aerobactin in the periplasm of fhuD, fhuB or fhuC mutant strains was not significantly lower than in the wild-type strain, but entry into the cytoplasm was greatly reduced in all cases. Uptake of aerobactin by strains wild-type for all transport functions occurred most efficiently in strains either lacking or specifically defective in the genetic determinants for aerobactin biosynthesis; significantly lower levels of exogenous 14C-labelled siderophore were observed in both compartments of strains producing aerobactin. Aerobactin-mediated 59Fe uptake, however, was not inhibited by the presence of endogenous aerobactin. Endogenous enterochelin did not affect aerobactin uptake.     

Synthesis and antifertility activity of ω-chain phenyl- and 16-phenoxy-analogues of (±)-11-deoxyprostaglandin F1α

Some ω-chain phenyl- and 16-phenoxy- analogues of (±)-11-deoxyprostaglandin F_1α have been synthesized and evaluated for anti-fertility activity in the hamster. 11-Deoxy-16-phenoxy-17,18,19,20-tetranor-PGF_1α was the most active member of the series with an ED₅₀ equal to that of PGF_2α. 11-Deoxy-17-phenyl-18,19,20-trinor-PGF_1α, which was one third as active as PGF_2α, was more potent than the corresponding 16- and 18-phenyl compounds. Aryl ring substitution was found to lower activity, except that with the 16-phenyl compound, p-bromo and m-trifluoromethyl substitution increased the potency.The antifertility activity of the phenoxy compounds, which were poor substrates for 15-hydroxyprostaglandin dehydrogenase, was shown to correlate well with the binding affinity for the bovine corpus luteum PGF_2α receptor. Some quantitative structure-activity data supporting this finding are presented.     

Opportunities to replace the use of animals in sepsis research. The report and recommendations of a Focus on Alternatives workshop

Sepsis and multiple organ failure are common causes of death in patients admitted to intensive care units. The incidence of sepsis and associated mortalities has been steadily increasing over the past 20 years. Sepsis is a complex inflammatory condition, the precise causes of which are still poorly understood. Animal models of sepsis have the potential to cause substantial suffering, and many of them have been poorly representative of the human syndrome. However, a number of non-animal approaches, including in vitro, in silico and clinical studies, show promise for addressing this situation. This report is based on discussions held at an expert workshop convened by Focus on Alternatives and held in 2004 at the Wellcome Trust, London. It provides an overview of some non-animal approaches to sepsis research, including their strengths and weaknesses, and argues that they should be prioritised for further development.     

Interaction between the CD8 coreceptor and major histocompatibility complex class I stabilizes T cell receptor-antigen complexes at the cell surface

The off-rate (k(off)) of the T cell receptor (TCR)/peptide-major histocompatibility complex class I (pMHCI) interaction, and hence its half-life, is the principal kinetic feature that determines the biological outcome of TCR ligation. However, it is unclear whether the CD8 coreceptor, which binds pMHCI at a distinct site, influences this parameter. Although biophysical studies with soluble proteins show that TCR and CD8 do not bind cooperatively to pMHCI, accumulating evidence suggests that TCR associates with CD8 on the T cell surface. Here, we titrated and quantified the contribution of CD8 to TCR/pMHCI dissociation in membrane-constrained interactions using a panel of engineered pMHCI mutants that retain faithful TCR interactions but exhibit a spectrum of affinities for CD8 of >1,000-fold. Data modeling generates a "stabilization factor" that preferentially increases the predicted TCR triggering rate for low affinity pMHCI ligands, thereby suggesting an important role for CD8 in the phenomenon of T cell cross-reactivity.     

Deciphering the complex three-way interaction between the non-integrin laminin receptor,galectin-3 and Neisseria meningitidis

The non-integrin laminin receptor (LAMR1/RPSA) and galectin-3 (Gal-3) are multi-functional host molecules with roles in diverse pathological processes, particularly of infectious or oncogenic origins. Using bimolecular fluorescence complementation and confocal imaging, we demonstrate that the two proteins homo- and heterodimerize, and that each isotype forms a distinct cell surface population. We present evidence that the 37 kDa form of LAMR1 (37LRP) is the precursor of the previously described 67 kDa laminin receptor (67LR), whereas the heterodimer represents an entity that is distinct from this molecule. Site-directed mutagenesis confirmed that the single cysteine (C¹⁷³) of Gal-3 or lysine (K¹⁶⁶) of LAMR1 are critical for heterodimerization. Recombinant Gal-3, expressed in normally Gal-3-deficient N2a cells, dimerized with endogenous LAMR1 and led to a significantly increased number of internalized bacteria (Neisseria meningitidis), confirming the role of Gal-3 in bacterial invasion. Contact-dependent cross-linking determined that, in common with LAMR1, Gal-3 binds the meningococcal secretin PilQ, in addition to the major pilin PilE. This study adds significant new mechanistic insights into the bacterial–host cell interaction by clarifying the nature, role and bacterial ligands of LAMR1 and Gal-3 isotypes during colonization.