Energy-dependent conformational change in the TolA protein of Escherichia coli involves its N-terminal domain, TolQ, and TolR.

TolQ, TolR, and TolA inner membrane proteins of Escherichia coli are involved in maintaining the stability of the outer membrane. They share homology with the ExbB, ExbD, and TonB proteins, respectively. The last is involved in energy transduction between the inner and the outer membrane, and its conformation has been shown to depend on the presence of the proton motive force (PMF), ExbB, and ExbD. Using limited proteolysis experiments, we investigated whether the conformation of TolA was also affected by the PMF. We found that dissipation of the PMF by uncouplers led to the formation of a proteinase K digestion fragment of TolA not seen when uncouplers are omitted. This fragment was also detected in Delta tolQ, Delta tolR, and tolA(H22P) mutants but, in contrast to the parental strain, was also seen in the absence of uncouplers. We repeated those experiments in outer membrane mutants such as lpp, pal, and Delta rfa mutants: the behavior of TolA in lpp mutants was similar to that observed with the parental strain. However, the proteinase K-resistant fragment was never detected in the Delta rfa mutant. Altogether, these results suggest that TolA is able to undergo a PMF-dependent change of conformation. This change requires TolQ, TolR, and a functional TolA N-terminal domain. The potential role of this energy-dependent process in the stability of the outer membrane is discussed.

Identification by genetic suppression of Escherichia coli TolB residues important for TolB-Pal interaction.

The Tol-Pal system of Escherichia coli is involved in maintaining outer membrane stability. Mutations in tolQ, tolR, tolA, tolB, or pal genes result in sensitivity to bile salts and the leakage of periplasmic proteins. Moreover, some of the tol genes are necessary for the entry of group A colicins and the DNA of filamentous bacteriophages. TolQ, TolR, and TolA are located in the cytoplasmic membrane where they interact with each other via their transmembrane domains. TolB and Pal form a periplasmic complex near the outer membrane. We used suppressor genetics to identify the regions important for the interaction between TolB and Pal. Intragenic suppressor mutations were characterized in a domain of Pal that was shown to be involved in interactions with TolB and peptidoglycan. Extragenic suppressor mutations were located in tolB gene. The C-terminal region of TolB predicted to adopt a beta-propeller structure was shown to be responsible for the interaction of the protein with Pal. Unexpectedly, none of the suppressor mutations was able to restore a correct association between Pal and peptidoglycan, suggesting that interactions between Pal and other components such as TolB may also be important for outer membrane stability.

The Tol proteins of Escherichia coli and their involvement in the uptake of biomolecules and outer membrane stability.

The Tol proteins of Escherichia coli are involved in outer membrane stability. They are also required for the uptake of the group A colicins and the translocation of filamentous phage DNA into the cytoplasm. The tol-pal genes constitute two operons in the E. coli genome, orfltolQRA and tolBpalorf2. The TolQ TolR TolA proteins form a complex in the cytoplasmic membrane, while TolB and Pal interact near the outer membrane. Most of the amino acid residues of TolA, TolB, TolR and Pal are localized in the periplasm. Recent advances in the knowledge of interactions of Tol-Pal proteins with other envelope components, or with group A colicins, are presented, together with current hypotheses about the role of the Tol proteins in outer membrane stability.

The reverse social distance scale.

A "reverse" Social Distance Scale was created by modifying Bogardus's Social Distance Scale, to measure minority groups' perceptions of the social distance established by the majority group between itself and minority groups. The Reverse Social Distance Scale (Guttman's coefficient of reproducibility = 0.99) differentiated between the African American students and the other two groups of minority students in the present sample--Hispanic students and Others--but did not differentiate between the latter two groups. The relationships between the participants' choices of self-identification terms and their scores on the Reverse Social Distance Scale were varied.

Dermatologic manifestations of HIV infection and AIDS.

Infection with HIV can result in many cutaneous disorders, some of which may be the presenting sign of the disease. The cutaneous manifestations may be infectious or noninfectious. This article reviews the numerous cutaneous infectious findings, neoplasms, and dermatoses seen in HIV-infected individuals.

Silent bowel perforation occurring during corticosteroid treatment for pemphigus vulgaris.

We present the case of a patient who experienced a silent colonic perforation while being treated for pemphigus vulgaris with prednisone and azathioprine. Dermatologists are experienced in the management of pemphigus vulgaris with prednisone. We report a well-recognized but rarely reported adverse effect of this standard therapy for pemphigus vulgaris.

Cutaneous infection with Mycobacterium avium-intracellulare scrofulaceum intermediate: a new pathogenic entity.

The atypical or environmental mycobacterial organisms constitute a large group of potential agents in the pathogenesis of cutaneous infection. The most commonly encountered mycobacterial infection after contact with water is Mycobacterium marinum. We report an unusual case of cutaneous mycobacterial infection caused by a newly described opportunistic mycobacteria, M. avium-intracellulare scrofulaceum intermediate. This case emphasizes the difficulty in distinguishing among the species M. avium-intracellulare, M. scrofulaceum, and M. gordonae.

Familial occurrence of lichen sclerosus et atrophicus. Case reports of a mother and daughter.

A mother and daughter with lichen sclerosus et atrophicus (LSA) are described. Both had lesions restricted to their lower legs. Both patients were positive for HLA-B40, which has been associated with LSA. Sex steroid hormones showed no decrease in dihydrotestosterone, free testosterone, or androstenedione levels in the daughter as was demonstrated in a previous study of this disease, but did show some decrease in androstenedione in the mother. This article provides further evidence for a possible familial predisposition for LSA.

Contact hypersensitivity reactions to dinitrofluorobenzene mediated by monoclonal IgE anti-DNP antibodies.

Several studies have suggested a possible role for IgE antibodies in the pathogenesis of cutaneous hypersensitivity reactions that reach maximum intensity 24 to 48 hr after antigen challenge. The recent availability of murine monoclonal IgE anti-hapten antibodies has made possible the direct examination of the range of cutaneous inflammatory reactions that can be mediated by such antibodies. We have examined the effects of passively sensitizing BALB/c mice with monoclonal IgE anti-dinitrophenyl (DNP) antibody 48 hr before antigen challenge. Inflammatory responses were assessed by measuring ear swelling in mice challenged on the ears with the reactive hapten 2,4-dinitrofluorobenzene (DNFB). Compared with unsensitized controls, the ears of mice passively sensitized with IgE anti-DNP displayed a biphasic pattern of ear swelling after DNFB challenge. An early, transient response (present within 15 to 30 min of challenge and returning to control levels within 4 to 9 hr) was followed by a second, more persistent increase in ear swelling that peaked 24 to 48 hr after challenge. This biphasic pattern of ear swelling seen in IgE-sensitized mice was temporally indistinguishable from that observed in mice conventionally sensitized for allergic contact dermatitis reactions by epicutaneous application of DNFB 5 days before DNFB ear challenge. Antigen specificity of the IgE-mediated contact hypersensitivity reactions was demonstrated by the failure of mice passively sensitized with IgE anti-DNP to display early or delayed ear swelling greater than unsensitized controls when challenged with either of two noncross-reacting haptens, fluorescein isothiocyanate or oxazolone. Mice passively sensitized with a monoclonal IgA anti-DNP antibody (MOPC 315) 48 hr before DNFB challenge failed to display early or delayed ear swelling greater than unsensitized controls. Heat inactivation of the IgE anti-DNP ascitic fluid at 56 degrees C for 30 min completely abolished its capacity to passively sensitize mice for contact hypersensitivity reactions after DNFB challenge. These results document the existence of an antigen-specific, IgE-mediated, delayed-in-time cutaneous hypersensitivity response that can be elicited by epicutaneous challenge (contract) with a reactive hapten.

Granular cell tumor.

The case report presented herein involves a granular cell tumor of the vulva, an uncommon site, with unusual clinical characteristics.