Fatty acid signals in Bacillus megaterium are attenuated by cytochrome P-450-mediated hydroxylation

In previous publications [English, Hughes and Wolf (1994) J. Biol. Chem. 269, 26836-26841; English, Hughes and Wolf (1996) Biochem. J. 316, 279-283], we have demonstrated that peroxisome proliferators and non-steroidal anti-inflammatory drugs are inducers of the cytochrome P-450BM-3 gene in Bacillus megaterium ATCC14581. Their mechanism of action involves binding to and subsequent displacement of the transcriptional repressor, Bm3R1, from its operator site, which results in the activation of cytochrome P-450BM-3 gene transcription. We now present evidence that the branched-chain fatty acid, phytanic acid, is a potent inducer of cytochrome P-450BM-3. We have also observed that phytanic acid and peroxisome proliferators are inducers of Bm3R1 protein accumulation and associated DNA-binding activity. In contrast, several barbiturates, although capable of inducing cytochrome P-450BM-3 and Bm3R1 gene transcription, were unable to induce the Bm3R1 protein. We also demonstrate that cytochrome P-450BM-3 readily oxidizes phytanic acid, and provide evidence that, although the omega-1 hydroxy acid derivatives of phytanic acid can associate with Bm3R1, they do so with an affinity two orders of magnitude lower than the unmodified fatty acid. As a consequence, the ability of the hydroxylated product to induce cytochrome P-450BM-3 gene expression in vivo is markedly reduced. These data collectively suggest that metabolism of fatty acids by cytochrome P-450BM-3 leads to an attenuation of their ability to activate the transcription of the BM-3 operon. This work places the action of bacterial fatty acid hydroxylases in an autoregulatory loop where they may be responsible for the inactivation or clearance of the inducing fatty acid signal.

Gloverin, an antibacterial protein from the immune hemolymph of Hyalophora pupae

Gloverin is an inducible antibacterial insect protein isolated from pupae of the giant silk moth Hyalophora. It is a basic (pI 8.5) protein with a molecular mass of 13.8 kDa, containing a large number of glycine residues (18.5%) but no cysteine, and has an amino acid sequence that reveals no strong degree of identity with any known proteins. Gloverin inhibits the growth of Escherichia coli at a minimal concentration of 1-3 microM, i.e. less than 5% of the concentration of gloverin in the hemolymph of infected pupae. The prime effect of gloverin, following its interaction with lipopolysaccharide (LPS) in the bacterial envelope, is a specific inhibition of the synthesis of vital outer membrane proteins, leading to an increased permeability of the outer membrane. The activity of gloverin is not affected by heating (100 degrees C, 10 min) but is inhibited by Mg2+ and by free LPS. The gloverin molecule will undergo conformational transitions from a monomeric random coil to an alpha-helix upon transfer from an aqueous to a hydrophobic environment, a property likely to be of importance for its interaction with cell-bound LPS. The activity of gloverin is in many respects similar to that of attacin, another antibacterial protein, originally found in Hyalophora [for a review see Boman, H. G., Faye, I., Gudmundsson, G. H., Lee, J.-Y. & Lindholm, D. A. (1991) Eur J. Biochem. 201, 23-31].

Inactivation of food microorganisms by high-pressure carbon dioxide treatment with or without explosive decompression

In order to elucidate the sterilization mechanism underlying the explosive decompression system, baker's yeast was pressurized with CO2, N2O, N2, or Ar gas at 40 atm and 40 degrees C for 4h, and then explosively discharged. The survival ratio was markedly decreased only by the treatments with CO2 and N2O, which are relatively soluble gases in water, suggesting that the microorganisms' death may be highly correlated with gas absorption by the cells. Lower decompression rates to atmospheric pressure, however, led to neither any lower reduction of remaining cells nor any smaller release of total cellular proteins. Furthermore, operating with a longer treatment time and smaller number of repetitions was usually more lethal than with a shorter time and more frequent repetition. From these results, most of the yeast cells appear to have been sterilized during the pressurization process. The spore cells of B. megaterium are considered to have been killed in a somewhat different manner, because of their distinct sensitivity to the applied gases.

The lantibiotic mersacidin inhibits peptidoglycan biosynthesis at the level of transglycosylation

The lantibiotic mersacidin has been previously reported to interfere with bacterial peptidoglycan biosynthesis, [Brötz, H., Bierbaum, G., Markus, A., Molitor, E. & Sahl, H.-G. (1995) Antimicrob. Agents Chemother. 39, 714-719]. Here, we focus on the target reaction and describe a mersacidin-induced accumulation of UDP-N-acetylmuramoyl-pentapeptide, indicating that inhibition of peptidoglycan synthesis occurs after the formation of cytoplasmic precursors. In vitro studies involving a wall-membrane particulate fraction of Bacillus megaterium KM demonstrated that mersacidin did not prevent the synthesis of lipid II [undecaprenyl-diphosphoryl-N-acetylmuramoyl-(pentapeptide)-N-ac ety lglucosamine] but specifically the subsequent conversion of this intermediate into polymeric nascent glycan strands by transglycosylation. Comparison with other inhibitors of transglycosylation shows that the effective concentration of mersacidin in vitro is in the range of that of the glycopeptide antibiotic vancomycin but 2-3 orders of magnitude higher than that of the competitive enzyme inhibitor moenomycin. The analogy to the glycopeptides may hint at an interaction of mersacidin with the peptidoglycan precursor rather than with the enzyme. Unlike vancomycin however, mersacidin inhibits peptidoglycan formation from UDP-N-acetylmuramoyl-tripeptide and is active against Enterococcus faecium expressing the vanA resistance gene cluster. This indicates that the molecular target site of mersacidin differs from that of vancomycin and that no cross-resistance exists between the two antibiotics.

Dihydroisocoumarins from fungi: isolation, structure elucidation, circular dichroism and biological activity

Five known and three new dihydroisocoumarins were isolated from different fungi. The new isocoumarins are 5-chloro-6-hydroxymellein, 5-chloro-4,6-dihydroxymellein and 5,6-dihydroxymellein. The absolute configuration of these secondary metabolites was confirmed by CD measurements and in two cases by X-ray structure analysis.

Selective lysis of bacteria but not mammalian cells by diastereomers of melittin: structure-function study

Studies on lipid-peptide interactions of cytolytic polypeptides tend to emphasize the importance of the amphipathic alpha-helical structure for their cytolytic activity. In this study, diasetereomers of the bee venom melittin (26 a.a.), a non-cell-selective cytolysin, were synthesized and investigated for their structure and cytolytic activity toward bacteria and mammalian cells. Similarly to the findings with the diastereomers of the less cytolytic peptide pardaxin (33 a.a.) (Shai & Oren. 1996), the melittin diastereomer, lest their alpha-helical structure, which abrogated their hemolytic activity toward human erythrocytes. However, they retained their antibacterial activity and completely lysed both Gram-positive and Gram-negative bacteria, as revealed by transmission electron microscopy. To understand the molecular mechanism underlying this selectivity, binding experiments utilizing the intrinsic tryptophan of melittin, tryptophan quenching experiments using brominated phospholipids, and membrane destabilization studies were done. The data revealed that the melittin diastereomers bound to and destabilized only negatively-charged phospholipid vesicles, in contrast to native melittin, which binds strongly to both negatively-charged and zwitterionic phospholipids. However, the partition coefficient, the depth of penetration into the membrane, and the membrane-permeating activity of the diastereomers with negatively-charged phospholipids were similar to those obtained with melittin. The results obtained do not support the formation of transmembrane pores as the mode of action of the diastereomers, but rather suggest that these peptides bind to the surface of the bacterial membrane, cover it in a "carpet-like" manner, and dissolve it like a detergent. The results presented here together with those obtained with the cytolytic peptide pardaxin suggest that the combination of hydrophobicity and net positive charge may be sufficient in the design of potent diastereomers of antibacterial polypeptides for the treatment of infectious diseases.

Induction of cytochrome P-450 BM-3 (CYP 102) by non-steroidal anti-inflammatory drugs in Bacillus megaterium

Bacillus megaterium contains a cytochrome P-450 fatty acid mono-oxygenase which is inducible with barbiturate drugs. We have demonstrated that this enzyme system is inducible with peroxisome proliferators. In mammals, peroxisome proliferators also induce mono-oxygenases in the CYP4A gene family. In this paper we demonstrate that the non-steroidal anti-inflammatory drugs ibuprofen, ketoprofen and indomethacin are potent inducers of fatty acid mono-oxygenase activity as well as of P-450BM-3 protein in B. megaterium. The levels of induction of P-450 protein were 11.8-, 3.9- and 3.0-fold respectively. In addition, we demonstrate that these inducing agents interact with a transcriptional repressor, Bm3R1, which leads to its dissociation from its operator sequence. This provides a rational mechanism for the induction process. This is the first report which demonstrates that non-steroidal anti-inflammatory drugs can interact directly with a transcription factor to initiate gene expression, and further substantiates the structure-activity relationships that identify inducers of cytochrome P-450BM-3 and compounds that have the potential to act as peroxisome proliferators and induce CYP4A expression in mammals.

A class of highly potent antibacterial peptides derived from pardaxin, a pore-forming peptide isolated from Moses sole fish Pardachirus marmoratus

Pardaxin, a 33-amino-acid pore-forming polypeptide toxin isolated from the Red Sea Moses sole Pardachirus marmoratus, has a helix-hinge-helix structure. This is a common structural motif found both in antibacterial peptides that can act selectively on bacterial membranes (e.g., cecropin), and in cytotoxic peptides that can lyse both mammalian and bacterial cells (e.g., melittin). Herein we show that pardaxin possesses a high antibacterial activity with a significantly reduced hemolytic activity towards human red blood cells (hRBC), compared with melittin. Its potency is comparable to that of other known native antibacterial peptides such as magainin, cecropins and dermaseptins. To determine the structural features responsible for the selective hemolytic and antibacterial activities, and the structural requirements for a high antibacterial activity, 8 truncated and modified pardaxin analogues were synthesized and structurally and functionally characterized. Each peptide was synthesized with a free carboxylate or amino group (i.e., aminated form) at its C-terminus. The aminated form of pardaxin has both high hemolytic and antibacterial activity. A truncated analogue, with 11 amino acids removed from the C-terminal domain, had dramatically reduced hemolytic activity. However, the aminated form of this analogue was significantly more potent that pardaxin against most bacteria tested, suggesting that the C-terminal tail of pardaxin is responsible for non-selective activity against erythrocytes and bacteria. Furthermore, a positive charge added to its N-terminus significantly increased its antibacterial activity and abolished its low hemolytic activity. The 22-amino-acid C-terminal domain and the short 11-amino-acid N-terminal domain were, in their aminated forms, active only against gram-positive bacteria. Secondary-structure determination using circular dichroism spectroscopy revealed that all the aminated analogues had 25-80% more alpha-helical content in 40% CF3CH2OH/water than their non-aminated forms. Using model phospholipid membranes it was found that all the analogues that were less hemolytic but had retained antibacterial activity could permeate acidicly charged phospholipid vesicles better than zwitterionic phospholipid vesicles, a property characteristics of all the native antibacterial peptides tested so far (e.g., cecropins, magainins and dermaseptins). Pardaxin and its analogues therefore represent a new class of antibacterial peptides that can serve as a basis for the design of therapeutic agents. Furthermore, negative-staining electron microscopy revealed that total inhibition of bacterial growth was due to total lysis of the bacterial wall. Therefore, it might be more difficult for bacteria to develop resistance to such a destructive mechanism, compared with the more specific mechanisms of the currently used antibiotics.

Diastereoisomers of cytolysins, a novel class of potent antibacterial peptides

An amphipathic alpha-helical structure is considered to be a prerequisite for the lytic activity of most short linear cytolytic polypeptides that act on both mammalian cells and bacteria. This structure allows them also to exert diverse pathological and pharmacological effects, presumably by mimicking protein components that are involved in membrane-related events. In this study D-amino acid-incorporated analogues (diastereomers) of the cytolysin pardaxin, which is active against mammalian cells and bacteria, were synthesized and structurally and functionally characterized. We demonstrate that the diastereomers do not retain the alpha-helical structure, which in turn abolishes their cytotoxic effects on mammalian cells. However, they retain a high antibacterial activity, which is expressed in a complete lysis of the bacteria, as revealed by negative staining electron microscopy. The disruption of the alpha-helical structure should prevent the diastereomer analogues from permeating the bacterial wall by forming transmembrane pores but rather by dissolving the membrane as a detergent. These findings open the way for a new strategy in developing a novel class of highly potent antibacterial polypeptides for the treatment of infectious diseases, due to the increasing resistance of bacteria to the available antibacterial drugs.

Paracelsin E, a new peptaibol from Trichoderma saturnisporum

The structure of paracelsin E, a new peptaibol from Trichoderma saturnisporum, has been determined primarily by fabms. The well-known paracelsins A, B, C, and D were also found in a culture of this organism.

The molecular cloning and characterization of BM1P1 and BM1P2 proteins, putative positive transcription factors involved in barbiturate-mediated induction of the genes encoding cytochrome P450BM-1 of Bacillus megaterium

Analysis of a 1.3-kilobase segment of 5'-flanking DNA from the barbiturate-inducible P450BM-1 gene (CYP106) of Bacillus megaterium revealed two open reading frames. One, BM1P1, encodes 98 amino acids and is located 267 base pairs upstream from the sequence encoding cytochrome P450BM-1 but in the opposite orientation. The second, BM1P2 (88 amino acids), is 892 base pairs upstream from the P450BM-1 coding sequence and in the same coding strand. The expression of BM1P1 and BM1P2 was strongly stimulated in cells grown in the presence of pentobarbital, and the BM1P1 gene product exerted positive control on expression of P450BM-1. When a 177-base pair fragment encompassing the overlapping promoter regions of the P450BM-1 and BM1P1 genes was used as a probe in DNA binding assays, the BM1P1 and BM1P2 gene products and Bm3R1 (the repressor protein regulating the barbiturate-mediated expression of P450BM-3) could bind individually, but the addition of BM1P1 or BM1P2 to a binding mixture containing Bm3R1 completely prevented the appearance of a Bm3R1 binding band. When a 208-base pair fragment containing a Barbie box sequence and located upstream of the 177-base pair fragment was used as a probe, only a Bm3R1 binding band was detected. Although neither BM1P1 and BM1P2 appeared to bind to this 208-base pair fragment, their presence strongly inhibited the binding of Bm3R1 to the same probe. The evidence suggests that BM1P1 and BM1P2 may, in part, act as positive regulatory proteins involved in the expression of the P450BM-1 gene by interfering with the binding of the repressor protein, Bm3R1, to the regulatory regions of P450BM-1.

Transcriptional regulation of the genes encoding cytochromes P450BM-1 and P450BM-3 in Bacillus megaterium by the binding of Bm3R1 repressor to Barbie box elements and operator sites

We previously reported (Liang, Q., He, J.-S., and Fulco, A.J. (1995) J. Biol. Chem. 270, 4438-4450) that Bm3R1, a repressor regulating the expression of P450BM-3 in Bacillus megaterium, could bind to Barbie box sequences in the 5'-flanking regions of barbiturate-inducible genes. We've now shown that pentobarbital does not inhibit in vitro binding of Bm3R1 to the P450BM-3 and P450BM-1 Barbie boxes (BB3 and BB1), although the palindromic operator sequence (OIII) of P450BM-3 did have a strong competitive effect on such binding. G39E-Bm3R1, a mutant of Bm3R1, did not bind to either Barbie box. In the presence of Bm3R1, portions of the regulatory regions of P450BM-3 and P450BM-1 were protected from DNase I digestion. These included 11 of the 15 base pairs of BB3 plus 7 base pairs 3' to BB3, BB1 plus 16 base pairs 3' to BB1, and, in the 5'-flanking region of P450BM-1, segments covering most of two palindromic sequences (OII and OIII) of 24 and 52 base pairs. These DNase I-protected regions (including OIII) showed considerable sequence identity, especially in a conserved poly(A) motif. Barbiturates did not inhibit binding of Bm3R1 to OI. OII in vitro while G39E-Bm3R1 did not bind. The regulatory effects of Bm3R1 on P450BM-1 and P450BM-3 were also evaluated in vivo using heterologous chloramphenicol acetyltransferase constructs and Western blotting. In the G39E mutant strain, both P450BM-1 and P450BM-3 were constitutively expressed, and the regulatory proteins Bm1P1 and Bm3P1, although still pentobarbital-inducible, had significantly higher basal levels of synthesis. In toto, our results show that Bm3R1 represses both P450BM-1 and P450BM-3 expression and that it may effect this by coordinate binding to operator and Barbie box sequences to produce looping of the P450BM-1 and P450BM-3 regulatory regions through protein-protein interaction.

Cooperative manganese (II) activation of 3-phosphoglycerate mutase of Bacillus megaterium: a biological pH-sensing mechanism in bacterial spore formation and germination

The conversion of 3-P-glycerate mutase of Bacillus megaterium from a catalytically inactive to an active form was markedly more effective with buffered Mn2+ than with just added Mn2+. The previously reported stimulation by threonine disappeared when buffered Mn2+ was used. Activation of mutase showed a sigmoid dependence on Mn2+ concentration when buffered with tetramethylenediamine tetraacetate. The curve obeyed Hill kinetics with a coefficient of 2.1 +/- 0.1. At 0.5 microM free Mn2+, buffered with trimethylenediamine tetraacetate, activation of mutase increased about 73-fold over the pH range 6.6 to 7.4. Plotted against [OH-], the activation showed a strongly sigmoid response with Hill coefficient of 3.5 +/- 0.1. When mutase activated at pH 6.4 and 0.5 microM free Mn2+ in the presence of substrate was transferred to a similar medium at pH 7.4, the rate of product accumulation increased 360-fold within a few minutes. The pH sensitivity conferred upon mutase by low [Mn2+] may account for its large activity decrease during sporulation, and later increase during spore germination, when spore pH, respectively, declines and rises by about 1 unit. These changes result in the accumulation, and later reutilization, of 3-P-glycerate reserves in the spore. Such a pH-sensing function of Mn2+ may have wider biological uses.

Processing of chromogranin B in bovine adrenal medulla. Identification of secretolytin, the endogenous C-terminal fragment of residues 614-626 with antibacterial activity

Chromogranins constitute a family of acidic soluble proteins widely distributed in endocrine cells and neurons. Chromogranin A, the major soluble component in bovine adrenal medullary secretory granules in chromaffin cells, has been shown to be actively processed to peptide fragments [Metz-Boutigue, M. H., Garcia-Sablone, P., Hogue-Angeletti, R. & Aunis, D. (1993) Eur. J. Biochem. 217, 247-257]. In the present paper, the structural features of the proteolytic degradation mechanism of chromogranin B/secretogranin I have been characterized with regard to the possible function of this protein as a precursor of biologically active peptides. Chromogranin-B-derived fragments present in bovine chromaffin granules were identified by microsequencing after separation by two-dimensional gel electrophoresis or high-performance liquid chromatography. A similar approach was performed to characterize chromogranin-B-derived fragments released into the extracellular space from depolarized bovine cultured chromaffin cells. In chromogranin B, 18 cleavage sites were identified along the protein chain and chromogranin B/secretogranin I fragments were generated by proteolytic attack at both the N-terminus and C-terminus. A major fragment corresponding to residues 614-626 of the C-terminal sequence, was identified in the extracellular space; this peptide was found to share sequence and structural similarities with the lytic domain of cecropins and, as expected from this similarity, to display potent antibacterial properties. Endogenous and synthetic peptides were active on Micrococus luteus, killing bacteria in the micromolar concentration range. The synthetic peptide slows the growth of Bacillus megaterium and was inactive towards Escherichia coli. In addition, the synthetic peptide was unable to induce hemolytic activity. This antibacterial function might be of biological significance in the neuroendocrine system of living organisms. We propose to name this peptide secretolytin.

The role of Barbie box sequences as cis-acting elements involved in the barbiturate-mediated induction of cytochromes P450BM-1 and P450BM-3 in Bacillus megaterium

In a previous publication (He, J.-S., and Fulco, A. J. (1991) J. Biol. Chem. 266, 7864-7869), we reported that a 15-17-base pair DNA sequence (designated a Barbie box element) in the 5'-regulatory regions of cytochrome P450BM-1 and P450BM-3 genes from Bacillus megaterium was recognized by a barbiturate-regulated protein. It is now recognized that essentially all eukaryotic and prokaryotic genes whose 5'-flanking regions are known and that encode barbiturate-inducible proteins contain the Barbie box element. A 4-base pair sequence (AAAG) is found in the same relative position in all Barbie box elements. In B. megaterium, mutation of the Barbie box located in the P450BM-1 gene leads to the constitutive synthesis of cytochrome P450BM-1 and a 10-fold increase of expression of Bm1P1, a small gene located upstream of the P450BM-1 gene, that encodes a putative regulatory protein. Mutation of the P450BM-3 Barbie box significantly increased the expression of both P450BM-3 and Bm3P1 (another small gene located upstream of the P450BM-3 gene that encodes a second putative regulatory protein) in response to pentobarbital induction but left the basal levels unaffected. In gel mobility shift assays, Bm3R1, a repressor of the P450BM-3 gene, was found to specifically interact with the Barbie box sequences of the B. megaterium P450 genes. Mutated Barbie boxes showed a decreased binding affinity for Bm3R1 compared to their wild type (unmutated) counterparts. Barbie box sequences were also shown to specifically interact with putative positive regulatory factors of B. megaterium cells. These putative positive factors were induced by pentobarbital and were also present at high levels during late stationary phase of B. megaterium cell cultures grown in the absence of barbiturates. The mutated Barbie box sequences had greater binding affinity for these positive factors than did unmutated Barbie box sequences. DNase I footprinting analysis of the 5'-flanking region of the P450BM-1 gene revealed that these positive factors protected a segment of DNA covering a portion of the Barbie box sequence and a small flanking region. Similar footprinting experiments with the 5'-flanking region of the P450BM-3 gene failed, however, to unambiguously reveal protected sequences in the Barbie box region. The evidence suggests that the positive factors and Bm3R1 compete with each other for binding to the Barbie box region, especially in the 5'-flanking region of the P450BM-1 gene, and for putative roles in the regulation of transcription from the B. megaterium P450 genes.(ABSTRACT TRUNCATED AT 400 WORDS)

On the domain structure of cytochrome P450 102 (BM-3): isolation and properties of a 45-kDa FAD/NADP domain

Cytochrome P450 102 is a catalytically self-sufficient monooxygenase isolated from barbiturate-induced Bacillus megaterium. The enzyme contains FAD, FMN, and heme in a single polypeptide chain of 1048 residues, and each of the cofactors is believed to be located in a separate domain. In the present study we have used exhaustive endogenous proteolysis to produce a 45 kDa fragment of the cytochrome. This fragment bound the 2',5'-adenosine diphosphate moiety of NADP(H) strongly, with approximately the same dissociation constant as in the native enzyme, and contained only FAD (0.93 equivalents per polypeptide, epsilon 453nm = 11,200 M-1cm-1). Reduction of the flavin by sodium dithionite proceeded quite slowly to yield FADH2, but no stable semiquinone species was produced upon air re-oxidation. In contrast, NADPH rapidly reduced this FAD/NADP(H) domain aerobically to produce the FADH. semiquinone radical. At a 75:1 molar ratio of the FAD/NADP(H) domain to the P450 102 heme domain, no laurate hydroxylase activity was observed. Gas-phase sequence analysis showed the presence of two major sequences beginning at Phe646 (403 residues, MW 45,033) and Asp652 (397 residues). These data are in agreement with the crystal structures of related enzymes and closely define the boundary of the FAD/NADP+ domain in P450 102.

Biological activity of amoebicin m4-A from Bacillus licheniformis M-4

Amoebicin m4-A from Bacillus licheniformis M-4 exerts a bactericidal and bacteriolytic action on Bacillus megaterium GR10. Protein, DNA, and RNA synthesis are inhibited, and the membrane electrical potential of this bacterium is depleted by amoebicin. Synthesis of DNA and RNA by Naegleria fowleri HB-1 is also inhibited. Liposomes constructed from L-alpha-phosphatidylcholine become permeable to ions, low-molecular-weight solutes, and high-molecular-weight polymers after treatment with amoebicin.

Affinity isolation and characterization of cytochrome P450 102 (BM-3) from barbiturate-induced Bacillus megaterium

Cytochrome P450 102 (BM-3) is a catalytically self-sufficient enzyme from Bacillus megaterium that is presently accepted as an important model of the mammalian microsomal P450 monooxygenase system. We have developed a novel affinity approach to purify P450 102 in a single chromatographic step and have studied the spectroscopic, catalytic, nucleotide binding, and crystallization properties of the highly purified enzyme. B. megaterium ATCC 14581 was grown to high cell density, and P450 102 was purified rapidly and in high yield by chromatography on adenosine-2',5'-diphosphate agarose from crude cell-free extract. The cytochrome bound to the column with remarkable avidity, in contrast to the significantly weaker binding observed for NADPH-cytochrome P450 reductase. Chromatographic behavior also showed that the cytochrome bound NADP(+)-type nucleotides more tightly than any other cellular polypeptide. The purified protein was electrophoretically homogeneous and had essentially theoretical contents of FAD, FMN, and heme. Optical spectra showed the expected heme and flavin absorption bands, and three previously undescribed charge-transfer-type absorptions were characterized. Molar extinction coefficients in the oxidized, fully reduced, and ferrous carbonyl states have been determined; notable is the large soret extinction in the ferrous carbonyl state (epsilon 449 nm = 143,500 M-1 cm-1). Final preparations were active in the oxidation of a wide variety of substrates. Of the C14 alkyl compounds studied, tetradecyltrimethylammonium bromide showed the highest substrate-dependent oxidation of NADPH, followed by myristate and myristyl alcohol; however, myristate exhibited the lowest Km value. Activities were tightly coupled to NADPH oxidation (> 97%). Phenobarbital, benzphetamine, cocaine, cyclohexane, methanol, ethanol, retinoic acid, benzoate, heptaflourobutyrate, and 7-ethoxycoumarin were not substrates. NADP+ titrations showed, as expected, that the coenzyme was bound very tightly, with an average Kd of 580 nM. Our preparations of P450 102 are of sufficient purity and stability that crystals of the native holoenzyme have been grown.

Isolation of three antibacterial peptides from pig intestine: gastric inhibitory polypeptide (7-42), diazepam-binding inhibitor (32-86) and a novel factor, peptide 3910

Two antibacterial peptides, cecropin P1 and PR-39 (39-residue proline/arginine-rich peptide), from the upper part of pig small intestine have previously been isolated and characterized. We have now continued our search for antibacterial peptides in different side fractions generated during the isolation of intestinal hormones. Starting from one such fraction and monitoring activity against Bacillus megaterium, we isolated three homogeneous peptides by three consecutive chromatographic steps. Amino acid sequence analysis in combination with mass spectrometry identified two of the peptides as gastric inhibitory polypeptide (7-42) [GIP(7-42)] and diazepam-binding inhibitor (32-86) [DBI(32-86)], derived from factors already known. However, intact GIP and DBI have hardly any antibacterial activity by themselves. The third peptide constitutes a previously unknown structure, designated as peptide 3910 from its molecular mass. All three peptides showed good activity against B. megaterium. In addition, GIP (7-42) showed some activity against Streptococcus pyogenes and an Escherichia coli mutant with a defect in its outer membrane.

Netropsin inhibits the increase of intracellular Ca(2+)-dependent serine proteinase activity in sporulating Bacillus megaterium

Netropsin suppressed the increase of intracellular proteolytic activity when added to B. megaterium incubated in a sporulation medium. The inhibited enzyme was a Ca(2+)-dependent serine proteinase. Sporulation and protein turnover in later sporulation phases were inhibited as well. Different concentrations of netropsin affected various aspects of protein catabolism differently.

Catabolite repression of the xyl operon in Bacillus megaterium

We characterized catabolite repression of the genes encoding xylose utilization in Bacillus megaterium. A transcriptional fusion of xylA encoding xylose isomerase to the spoVG-lacZ indicator gene on a plasmid with a temperature-sensitive origin of replication was constructed and efficiently used for single-copy replacement cloning in the B. megaterium chromosome starting from a single transformant. In the resulting strain, beta-galactosidase expression is 150-fold inducible by xylose and 14-fold repressed by glucose, showing that both regulatory effects occur at the level of transcription. Insertion of a kanamycin resistance gene into xylR encoding the xylose-dependent repressor leads to the loss of xylose-dependent regulation and to a small drop in the efficiency of glucose repression to eightfold. Deletion of 184 bp from the 5' part of the xylA reading frame reduces glucose repression to only twofold. A potential glucose-responsive element in this region is discussed on the basis of sequence similarities to other glucose-repressed genes in Bacillus subtilis. The sequence including the glucose-responsive element is also necessary for repression exerted by the carbon sources fructose and mannitol. Their efficiencies of repression correlate to the growth rate of B. megaterium, as is typical for catabolite repression. Glycerol, ribose, and arabinose exert only a basal twofold repression of the xyl operon, which is independent of the presence of the cis-active glucose-responsive element within the xylA reading frame.

Barbiturate-mediated regulation of expression of the cytochrome P450BM-3 gene of Bacillus megaterium by Bm3R1 protein

In a previous publication (Wen, L.-P., Ruettinger, R. T., and Fulco, A.J. (1989) J. Biol. Chem. 264, 10996-11003), we reported that about 1 kilobase of 5' flanking sequence was required for barbiturate-inducible expression of the cytochrome P450BM-3 gene in Bacillus megaterium. We have now found, by analysis of various deletion and frameshift derivatives of this region, that an open reading frame immediately upstream of the B. megaterium cytochrome P450BM-3 structural gene encodes a protein, designated Bm3R1, which negatively controls the expression of the P450BM-3 gene at the transcriptional level. A helix-turn-helix DNA binding motif was found near the N-terminal portion of Bm3R1 protein. The 5' terminus of the bm3R1 transcript generated in vivo was determined by nuclease S1 mapping and primer extension analysis to be 44 base pairs upstream of the translation initiation sequence GTG of bm3R1. A putative promoter sequence with a high degree of similarity to the -35 and -10 consensus sequence recognized by the Bacillus subtilis sigma-43 factor was located at an appropriate distance from the transcription start site. A B. megaterium mutant which highly constitutively produced P450BM-3 protein was isolated and complementation of this cytochrome P450BM-3-constitutive mutant by a DNA fragment containing the wild-type bm3R1 gene indicated that the mutation in this locus was trans-dominant. Sequence analysis of the bm3R1 gene and its upstream region from this mutant, after amplification by the polymerase chain reaction, identified a single base change that resulted in a glycine to glutamate substitution in the beta-turn region of the DNA binding motif. By placing the bm3R1 gene under the control of a tac promoter and changing the translation initiation sequence from GTG to ATG, we succeeded in overproducing the Bm3R1 protein in Escherichia coli. A 20-bp perfect palindromic putative operator site, located between the presumed promoter sequences and the bm3R1 structural gene, was defined both by in vivo titration of Bm3R1 repressor and by gel mobility shift assays using the cell-free extracts containing the overproduced wild-type or mutant Bm3R1 protein. The barbiturate effect in mediating the induction of cytochrome P450BM-3 appears to be indirect but probably involves, in part, the release of inhibition by Bm3R1 repressor protein by interfering with its binding to the palindromic putative operator sequence and perhaps to other sites on the regulatory region of the gene encoding cytochrome P450BM-3.

Inhibition of membrane potential-dependent amino acid transport by daptomycin

Daptomycin inhibits the formation of UDP-N-acetylmuramyl-pentapeptide in Bacillus megaterium by inhibiting active transport of amino acids incorporated into the pentapeptide. The ability of daptomycin to inhibit active transport and peptidoglycan formation may be due to its ability to disrupt the transmembrane electrochemical gradient.

Evaluation of a dental unit with a built-in decontamination system

The efficacy of a dental unit equipped with a system that disinfects and sterilizes the water tubing by flushing with glutaraldehyde was evaluated by inserting Bacillus megaterium spores and Pseudomonas and Moraxella species into the water tubing. Up to 10(8) Pseudomonas and Moraxella organisms were killed during the disinfection cycle, but Bacillus megaterium spores were not. Up to 10(5) spores were eradicated by the sterilization cycle, although the system did not consistently kill 10(8) spores. The water tubing of the new unit was not naturally colonized by water bacteria during an 8-month period prior to the study. Evidence suggested that this was due to antimicrobial activity associated with the plastic tubing; therefore, microbial contamination of new dental units, irrespective of their design, would not be expected, until the inhibitory factor in the plastic tubing has leached out.