Chemoproteomic identification of a DPP4 homolog in Bacteroides thetaiotaomicron

Serine hydrolases have important roles in signaling and human metabolism, yet little is known about their functions in gut commensal bacteria. Using bioinformatics and chemoproteomics, we identify serine hydrolases in the gut commensal Bacteroides thetaiotaomicron that are specific to the Bacteroidetes phylum. Two are predicted homologs of the human dipeptidyl peptidase 4 (hDPP4), a key enzyme that regulates insulin signaling. Our functional studies reveal that BT4193 is a true homolog of hDPP4 that can be inhibited by FDA-approved type 2 diabetes medications targeting hDPP4, while the other is a misannotated proline-specific triaminopeptidase. We demonstrate that BT4193 is important for envelope integrity and that loss of BT4193 reduces B. thetaiotaomicron fitness during in vitro growth within a diverse community. However, neither function is dependent on BT4193 proteolytic activity, suggesting a scaffolding or signaling function for this bacterial protease.

Strategies for Tuning the Selectivity of Chemical Probes that Target Serine Hydrolases

Serine hydrolases comprise a large family of enzymes that have diverse roles in key cellular processes, such as lipid metabolism, cell signaling, and regulation of post-translation modifications of proteins. They are also therapeutic targets for multiple human pathologies, including viral infection, diabetes, hypertension, and Alzheimer disease; however, few have well-defined substrates and biological functions. Activity-based probes (ABPs) have been used as effective tools to both profile activity and screen for selective inhibitors of serine hydrolases. One broad-spectrum ABP containing a fluorophosphonate electrophile has been used extensively to advance our understanding of diverse serine hydrolases. Due to the success of this single reagent, several robust chemistries have been developed to further diversify and tune the selectivity of ABPs used to target serine hydrolases. In this review, we highlight approaches to identify selective serine hydrolase ABPs and suggest new synthetic methodologies that could be applied to further advance probe development.

High metabolization of catecholestrogens by type 1 estrogen sulfotransferase (hEST1)

Recently, two types of estrogen sulfotransferase, chronologically named types 1 and 2 estrogen sulfotransferase (hEST1 and hEST2), have been described. Since hEST2 selectively catalyzes the sulfonation of ethinyl estradiol as well as that of estrone (E1) and estradiol (E2), but poorly the sulfonation of catecholestrogens, we wanted to assess the ability of hEST1 to metabolize these compounds. We overexpressed hEST1 in Escherichia coli in fusion with GST, then purified the enzyme using a glutathione affinity column, and obtained GST-free enzyme by digestion with thrombin. Using [35S]-phosphosadenosine phosphosulfate (PAPS) as cofactor, we showed that hEST1 efficiently metabolizes the transformation of 2-OH-E2 and 2-OH-E1. However, the transformation of 4-OH-E1 and 4-OH-E2 is much less efficient. Our results also show that hEST1 metabolizes more efficiently E2 than E1. Since hEST1 mRNA is produced from the same gene as MPST using different alternative promoters and since it is expressed in most breast cancer cells (MCF-7, ZR-75-1, T47-D, MDA-231, and MDA-418), studies of the expression and activity of hEST1 will be most important to have a better knowledge about its involvement in the control of the genotoxicity of estrogens and catecholestrogens.

Thermal modeling of microwave heated packed and fluidized bed catalytic reactors

Thermal models of small-scale, microwave-heated, packed-bed and fluidized-bed catalytic chemical reactors were developed to investigate the possibility of selectively heating the catalyst sites or the catalyst pellets with microwaves. Results indicate catalyst sites may be selectively heated under special conditions in a packed or fluidized bed, and catalyst pellets may be heated above the temperature of the cooling(and reacting) gas under certain conditions in a fluidized bed.

Antibodies to Merkel cells in human sera. Incidence and significance

Antibodies to Merkel cells (MC) are not known to occur in human sera. Using a newly described technic, we looked for the presence of antibodies directed against skin structures in sera from 2,300 patients with various dermatologic and hematologic disorders, as well as graft-versus-host disease (GVHD). Three of these sera (0.1%) were found to react with MC. One monoclonal IgM antibody was present in serum obtained from a patient with chronic cold agglutinin disease, the second from a patient with GVHD, and the third from a patient with pemphigus vulgaris. The present inadequate knowledge about normal MC function and the absence of described symptoms of MC dysfunction preclude analysis of the pathogenic significance of these MC antibodies in human sera.

Dermatosis of hairless rats fed a hypomagnesic diet--pathology and immunology

The histopathology of hypomagnesic dermatosis in the hairless rat was studied on semithin sections, by electron microscopy, direct immunofluorescence and monoclonal antibodies to T cell subsets. We found primarily an edema of the epidermis and of the superficial dermis with a moderate mononuclear infiltrate and sometimes intraepidermal splits. The immunofluorescent study did not reveal any significant immune reactant within the skin. The comparison of our findings with the histopathology of the atopic dermatitis did not allow us to propose the hypomagnesic dermatosis as an animal model for human atopic dermatitis. We discuss some aspects of the pathogenesis of this chronic inflammatory dermatosis.