Study of the antagonistic action of actinomycetes on anthrax bacilli

Capacity for the growth inhibition of the highly virulent causative agent of Siberia plague was studied with respect to actinomycetous strains from soil samples of the Ukraine. It was found that on nutrient media 88.4, 88.9, 88.1 and 93.4% of the isolates inhibited the growth of Bac. anthracis, Bac. cereus, Bac. mycoides and Tsenkovsky vaccine strain respectively. Representatives of very different taxonomic groups were found among the antagonistic actinomycetes. Clearance of the soil from Siberia plague bacilli stable to the outer effect with the help of the active strain L-721 of Act. chromofuscus was observed. The effect was chown in sterilized soil, not sterile soil and soil monolith.     

Synthesis and preliminary antimicrobial screening of two thiosulfonates

Tetramethylene bis(methanethiosulfonate), the S-ester analog of busulfan, was prepared by reacting 1,4-dibromobutane with potassium methanethiosulfonate. 2,4-Dichlorophenyl methanethiosulfonate was prepared by reacting sodium methanesulfinate with 2,4-dichlorobenzenesulfenyl chloride. Neither compound showed antifungal activity against Microsporum audouini or Trichophyton mentagrophytes. Although tetramethylene bis(methanethiosulfonate) was more active against Staphylococcus aureus than was 2,4-dichlorophenyl methanethiosulfonate, neither compound was as active as the streptomycin control.     

Core domain mutation (S86Y) selectively inactivates polyubiquitin chain synthesis catalyzed by E2-25K

The mammalian ubiquitin conjugating enzyme known as E2-25K catalyzes the synthesis of polyubiquitin chains linked exclusively through K48-G76 isopeptide bonds. The properties of truncated and chimeric forms of E2-25K suggest that the polyubiquitin chain synthesis activity of this E2 depends on specific interactions between its conserved 150-residue core domain and its unique 50-residue tail domain [Haldeman, M. T., Xia, G., Kasperek, E. M., and Pickart, C. M. (1997) Biochemistry 36, 10526-10537]. In the present study, we provide strong support for this model by showing that a point mutation in the core domain (S86Y) mimics the effect of deleting the entire tail domain: the ability to form an E2 approximately ubiquitin thiol ester is intact, while conjugation activity is severely inhibited (>/=100-fold reduction in kcat/Km). The properties of E2-25K enzymes carrying the S86Y mutation indicate that this mutation strengthens the interaction between the core and tail domains: both free and ubiquitin-bound forms of S86Y-25K are completely resistant to tryptic cleavage at K164 in the tail domain, whereas wild-type enzyme is rapidly cleaved at this site. Other properties of S86Y-26K suggest that the active site of this mutant enzyme is more occluded than the active site of the wild-type enzyme. (1) Free S86Y-25K is alkylated by iodoacetamide 2-fold more slowly than the wild-type enzyme. (2) In assays of E2 approximately ubiquitin thiol ester formation, S86Y-25K shows a 4-fold reduced affinity for E1. (3) The ubiquitin thiol ester adduct of S86Y-25K undergoes (uncatalyzed) reaction with dithiothreitol 3-fold more slowly than the wild-type thiol ester adduct. One model to accommodate these findings postulates that an enhanced interaction between the core and tail domains, induced by the S86Y mutation, causes a steric blockade at the active site which prevents access of the incoming ubiquitin acceptor to the thiol ester bond. Consistent with this model, the S86Y mutation inhibits ubiquitin transfer to macromolecular acceptors (ubiquitin and polylysine) more strongly than transfer to small-molecule acceptors (free lysine and short peptides). These results suggest that unique residues proximal to E2 active sites may influence specific function by mediating intramolecular interactions.