Photobacterium damselae subspecies damselae Pneumonia in Dead, Stranded Bottlenose Dolphin, Eastern Mediterranean Sea.

Photobacterium damselae subspecies damselae, an abundant, generalist marine pathogen, has been reported in various cetaceans worldwide. We report a bottlenose dolphin in the eastern Mediterranean Sea that was found stranded and dead. The dolphin had a severe case of chronic suppurative pneumonia and splenic lymphoid depletion caused by this pathogen.

Reversal of cystoid macular edema in gyrate atrophy patients.

PURPOSE: This study reports the presentation of two families with gyrate atrophy (GA). The aim of this study was to characterize the potential effect of therapeutic regimens on macular edema. METHODS: Two unrelated patients with GA were studied for the potential effect of low protein diet (≤ 0.8 g/kg/d), and oral administration of pyridoxine (500 mg/day), on serum ornithine levels, best corrected visual acuity (BCVA), slit-lamp, OCT, and auto-fluorescence findings. Blood samples for DNA, mRNA, and exons of the OAT gene were screened for mutations and splicing effect when relevant. RESULTS: At presentation, both patients manifested typical ophthalmic features of GA including cystoid macular edema (CME). One patient also exhibited optic nerve head hamartoma. Following treatment ornithine levels have lessened, BCVA improved, and central macular thickness (CMT) markedly decreased in all four studied eyes. The molecular pathologic features included a novel splice site mutation (c.900+1G>A). CONCLUSIONS: We have identified a novel mutation and two formerly described mutations in patients with GA. Of them, one patient comprised an unusual phenotype including bilateral astrocytic hamartomas. We have recognized for the first time improvement in CME following treatment with low protein intake and pyridoxine supplement. This finding may have significance in the understanding of treatment options for macular edema regardless of underlying etiology.

CD28: direct and critical receptor for superantigen toxins.

Every adaptive immune response requires costimulation through the B7/CD28 axis, with CD28 on T-cells functioning as principal costimulatory receptor. Staphylococcal and streptococcal superantigen toxins hyperstimulate the T-cell-mediated immune response by orders of magnitude, inducing a lethal cytokine storm. We show that to elicit an inflammatory cytokine storm and lethality, superantigens must bind directly to CD28. Blocking access of the superantigen to its CD28 receptor with peptides mimicking the contact domains in either toxin or CD28 suffices to protect mice effectively from lethal shock. Our finding that CD28 is a direct receptor of superantigen toxins broadens the scope of microbial pathogen recognition mechanisms.

Topology determination of untagged membrane proteins.

The topology of integral membrane proteins with a weak topological tendency can be influenced when fused to tags, such as these used for topological determination or protein purification. Here, we describe a technique for topology determination of an untagged membrane protein. This technique, optimized for bacterial cells, allows the visualization of the protein in the native environment and incorporates the substituted-cysteine accessibility method.

New substrates on the block: clinically relevant resistances for EmrE and homologues.

Transporters of the small multidrug resistance (SMR) family are small homo- or heterodimers that confer resistance to multiple toxic compounds by exchanging substrate with protons. Despite the wealth of biochemical information on EmrE, the most studied SMR member, a high-resolution three-dimensional structure is missing. To provide proteins that are more amenable to biophysical and structural studies, we identified and partially characterized SMR transporters from bacteria living under extreme conditions of temperature and radiation. Interestingly, these homologues as well as EmrE confer resistance to streptomycin and tobramycin, two aminoglycoside antibiotics widely used in clinics. These are hydrophilic and clinically important substrates of SMRs, and study of their mode of action should contribute to understanding the mechanism of transport and to combating the phenomenon of multidrug resistance. Furthermore, our study of one of the homologues, a putative heterodimer, supports the suggestion that in the SMR family, heterodimers can also function as homodimers.

Binding of superantigen toxins into the CD28 homodimer interface is essential for induction of cytokine genes that mediate lethal shock.

Bacterial superantigens, a diverse family of toxins, induce an inflammatory cytokine storm that can lead to lethal shock. CD28 is a homodimer expressed on T cells that functions as the principal costimulatory ligand in the immune response through an interaction with its B7 coligands, yet we show here that to elicit inflammatory cytokine gene expression and toxicity, superantigens must bind directly into the dimer interface of CD28. Preventing access of the superantigen to CD28 suffices to block its lethality. Mice were protected from lethal superantigen challenge by short peptide mimetics of the CD28 dimer interface and by peptides selected to compete with the superantigen for its binding site in CD28. Superantigens use a conserved ß-strand/hinge/α-helix domain of hitherto unknown function to engage CD28. Mutation of this superantigen domain abolished inflammatory cytokine gene induction and lethality. Structural analysis showed that when a superantigen binds to the T cell receptor on the T cell and major histocompatibility class II molecule on the antigen-presenting cell, CD28 can be accommodated readily as third superantigen receptor in the quaternary complex, with the CD28 dimer interface oriented towards the ß-strand/hinge/α-helix domain in the superantigen. Our findings identify the CD28 homodimer interface as a critical receptor target for superantigens. The novel role of CD28 as receptor for a class of microbial pathogens, the superantigen toxins, broadens the scope of pathogen recognition mechanisms.

Topologically random insertion of EmrE supports a pathway for evolution of inverted repeats in ion-coupled transporters.

Inverted repeats in ion-coupled transporters have evolved independently in many unrelated families. It has been suggested that this inverted symmetry is an essential element of the mechanism that allows for the conformational transitions in transporters. We show here that small multidrug transporters offer a model for the evolution of such repeats. This family includes both homodimers and closely related heterodimers. In the former, the topology determinants, evidently identical in each protomer, are weak, and we show that for EmrE, an homodimer from Escherichia coli, the insertion into the membrane is random, and dimers are functional whether they insert into the cytoplasmic membrane with the N- and C-terminal domains facing the inside or the outside of the cell. Also, mutants designed to insert with biased topology are functional regardless of the topology. In the case of EbrAB, a heterodimer homologue supposed to interact antiparallel, we show that one of the subunits, EbrB, can also function as a homodimer, most likely in a parallel mode. In addition, the EmrE homodimer can be forced to an antiparallel topology by fusion of an additional transmembrane segment. The simplicity of the mechanism of coupling ion and substrate transport and the few requirements for substrate recognition provide the robustness necessary to tolerate such a unique and unprecedented ambiguity in the interaction of the subunits and in the dimer topology relative to the membrane. The results suggest that the small multidrug transporters are at an evolutionary junction and provide a model for the evolution of structure of transport proteins.