Physiological Studies of Cellulase (Avicelase) Synthesis in Streptomyces reticuli

Cellulase (Avicelase, Cel1) from Streptomyces reticuli efficiently hydrolyzes crystalline cellulose (Avicel) to cellobiose. The synthesis of the enzyme was found to be dependent on the presence of insoluble Avicel but not on either soluble hydroxyethylcellulose, cellooligomers, or cellobiose. Glycerol and various metabolizable mono- and disaccharides repress Avicelase synthesis, whereas yeast extract has no inducing or repressing effect. Glucose kinase is not required for the repression effect. In the course of cultivation, S. reticuli secretes significant quantities of acid, predominantly pyruvate and succinate, which reduce the pH to 4 in commonly used media with low buffering capacity. Comparative studies with media with low and high buffering capacities revealed that Avicelase synthesis is strongly repressed at a low pH.

A Simple and Rapid Method of Transformation of Streptomyces rimosus R6 and Other Streptomycetes by Electroporation

Usually plasmid DNA is introduced into Streptomyces strains by polyethylene glycol-mediated transformation of protoplasts. However, many Streptomyces strains are only poorly or not at all transformable via protoplasts. Therefore, we have optimized the parameters critical for the application of electrotransformation of plasmid DNA into Streptomyces species. The most critical parameters evaluated for electrotransformation of the model strain Streptomyces rimosus R6 were the pretreatment of mycelia, buffer composition, and electric field strength. The electrocompetent mycelia were prepared from 24-h-old cultures, treated mildly with lysozyme, resuspended in sucrose-glycerol-polyethylene glycol buffer, and stored in aliquots at -70 deg C. The electric field strength of 10 kV/cm at 400 (Omega) and a capacitance of 25 (mu)F was applied. The method is simple and rapid, yielding transformant colonies in 48 to 72 h. Efficiencies of 10(sup5) to 10(sup6) transformants per (mu)g of plasmid DNA were reproducibly achieved for S. rimosus R6 and its mutants, and these numbers were 10(sup2) to 10(sup3) higher than those attained by polyethylene glycol-assisted transformation of protoplasts. In addition, we show that electroporation can be applied to other Streptomyces species, such as S. lividans 66, S. coelicolor A3(2), and an S. venezuelae strain. This last one could not be transformed by the standard protoplast procedure. Our data suggest that, because of the diversity of streptomycetes, the conditions have to be optimized for each strain.

Identification of Mycelium-Associated Cellulase from Streptomyces reticuli

Among 180 Streptomyces strains tested, 25 were capable of hydrolyzing microcrystalline cellulose (Avicel) at 30 degrees C. Streptomyces reticuli was selected for further studies because of its ability to grow at between 30 and 50 degrees C on Avicel. Enzymatic activities degrading Avicel, carboxymethyl cellulose, and cellobiose were found both in the culture supernatant and in association with the mycelium and crystalline substrate. The bound enzymes were efficiently solubilized by repeated washes with buffer of low ionic strength (50 mM Tris hydrochloride [pH 7.5]) and further purified by fast protein liquid chromatography. A high-molecular-weight Avicelase of >300 kilodaltons could be separated from carboxymethyl cellulase (CMCase) and beta-glucosidase activities (molecular mass, 40 to 50 kilodaltons) by gel filtration on Superose 12. The CMCase fraction was resolved by Mono Q anion-exchange chromatography into two enzymes designated CMCase 1 and CMCase 2. The beta-glucosidase activity was found to copurify with CMCase 2. The purified cellulase components showed optimal activity at around pH 7.0 and temperatures of between 45 and 50 degrees C. Avicelase (but not CMCase) activity was stimulated significantly by the addition of CaCl(2).

Mutational analysis of the binding affinity and transport activity for N -acetylglucosamine of the novel ABC transporter Ngc in the chitin-degrader Streptomyces olivaceoviridis

The highly differentiated bacterium Streptomyces olivaceoviridis efficiently hydrolyses chitin, a highly abundant natural polysaccharide, to low molecular weight products including N-acetylglucosamine (NAG) and N,N' -diacetylchitobiose (chitobiose). NAG is taken up by a PTS (phosphoenolpyruvate-dependent phosphotransferase system) which includes the PtsC2 protein, and via the ABC (ATP-binding cassette) transporter Ngc, which itself includes the substrate-binding protein NgcE. This is at present the only ABC transporter which is known to mediate specific uptake of NAG (K(m) 0.48 microM, V(max) 1.3 nmol/min/mg dry weight) and is competitively inhibited by chitobiose (K(i) 0.68 microM). The latter finding suggests that the Ngc system transports both NAG and chitobiose efficiently. To identify amino acid residues required for the function of NgcE, either the wild-type or one of several mutant forms of the ngcE gene was introduced into the strain S. olivaceoviridis DeltaNgcE/DeltaPtsC1/DeltaPtsC2, which lacks both functional transport systems for NAG, and chromosomal recombinants were selected. Based on the in vivo transport parameters of the recombinants, and the in vitro binding characteristics of the corresponding purified proteins, the following conclusions can be drawn. (1) Replacement of the C-terminally located residue Y396 by A (Y396A) has little effect on ligand-binding or transport parameters. The W395A mutation also induced little change in the substrate affinity in vitro, but it led in vivo to a marked increase (11 fold) in K(m), and enhanced V(max) (by 1.5 fold). (2) The amino acids Y201 and W280 both contribute (51% and 38%) to the ligand-binding capacity of NgcE. They are both very important for the in vivo function of the complete transport apparatus; strains expressing either Y201A or W280A show drastically (100 or 150 times) enhanced K(m) values. (3) The concomitant presence of either Y200 and W280 or Y201 and W280 is essential for the function of NgcE. (4) Y201 is located within a tyrosyl-rich motif. This has been found to share some features with the ligand-binding site of amelogenins (enamel matrix proteins), which interact with NAG residues in glycoconjugates. In addition, it is distantly related to the ligand-binding site(s) in the plant-lectins UDA ( Urtica dioicaagglutinin, specific for NAG and its oligomers) and WGA (wheat germ agglutinin, which recognises a motif comprising three consecutive NAG residues).

Amino acid residues involved in reversible thiol formation and zinc ion binding in the Streptomyces reticuli redox regulator FurS

Streptomyces reticuli produces a mycelium-associated enzyme, CpeB, whose N-terminal and C-terminal portions mediate heme-dependent catalase-peroxidase and heme-independent manganese-peroxidase activities, respectively. The regulator FurS governs transcription of the furS- cpeB operon. The thiol form of FurS contains one zinc ion per monomer and binds in this state to its cognate operator. Oxidation of SH groups within FurS induces the release of the zinc ion. Substitution of the codons for the amino acids cysteine 96, histidine 92 and 93, and tyrosine 59 in furS disrupts the in vivo repressor activity of FurS and results in enhanced synthesis of CpeB in corresponding S. lividans transformants. Biochemical and footprinting studies with FurS and its mutant derivatives revealed that the cysteine residues 96 and 99 are involved in reversible S-S bond formation, while cysteine 96 and the histidine residues 92 and 93 are required for zinc coordination, and tyrosine 59 is necessary for the binding of FurS to DNA. On the basis of these data, functional predictions can be made for the mycobacterial regulator FurA, a close homologue of FurS.

Streptomyces olivaceoviridis possesses a phosphotransferase system that mediates specific, phosphoenolpyruvate-dependent uptake of N-acetylglucosamine

We recently described the ABC transporter Ngc (encoded by the ncgEFG operon) from Streptomyces olivaceoviridis, the first of its kind to be shown to transport N-acetylglucosamine and N,N'-diacetylchitobiose (chitobiose). A chromosomal mutant carrying a disruption of the ngcE gene, which encodes the sugar binding protein, was still able to transport N-acetylglucosamine. This phenotype can now be attributed to a functional phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS). Two adjacent homologous genes, ptsC1 and ptsC2, were identified, and deduced to encode proteins which are 56% identical and can be predicted to contain eight transmembrane regions. PtsC1 (432 amino acids) and PtsC2 (403 residues) each correspond to a single EIIC domain; such domains are otherwise known only in several bacterial multidomain permeases for glucose/mannose or N-acetylglucosamine. The C-terminal sequences of PtsC1 and PtsC2 correspond to the motifs LKTPGREP and LPTRGRES, respectively. The ptsB gene located upstream of ptsC1 is predicted to encode a homologue of the EIIB domains usually found in bacterial multidomain permeases. Physiological and biochemical analyses of ngcE mutants carrying disruptive insertions in ptsC1 or ptsC2 or both revealed that, when grown on N-acetylglucosamine, the membrane component PtsC2, unlike PtsC1, mediates PEP-dependent, specific (K(m)=5 micro M) transport of N-acetylglucosamine, but not of other hexoses. Cross-complementation of membrane and cytoplasmic fractions from the various mutants led to the conclusion that S. olivaceoviridis also expresses the functional soluble components HPr, EI and EIIA of the PTS system. During growth on xylose, uptake of this pentose occurred if ptsC1 or ptsC2 was intact, but not in a mutant containing disrupted forms of both genes.

The novel Streptomyces olivaceoviridis ABC transporter Ngc mediates uptake of N-acetylglucosamine and N,N'-diacetylchitobiose

During cultivation in the presence of N-acetylglucosamine or chitin, Streptomyces olivaceoviridis mycelium efficiently takes up [(14)C]-labelled N-acetylglucosamine. Uptake of the labelled compound can be completely inhibited by unlabelled N-acetylglucosamine and partially by chitobiose. After extraction of the membrane with Triton X-100, two forms of a protein that binds to N-acetylglucosamine and N, N'-diacetylchitobiose (chitobiose) were purified to homogeneity by two consecutive rounds of anionic exchange chromatography. The protein was named NgcE. Using surface plasmon resonance, its binding parameters were determined. It showed highest affinity for N-acetylglucosamine (K(D)=8.28 x 10(-9) M) and for chitobiose (K(D)=2.87 x 10(-8) M). Varying equilibrium dissociation constants in the micromolecular range were ascertained for chitotetraose (K(D)=4.5 x 10(-6) M), chitopentaose (K(D)=1.03 x 10(-6) M) and chitohexaose (K(D)=3.02 x 10(-6) M); the lowest value was measured for chitotriose (K(D)=19.4 x 10(-6) M). After having determined the sequences of several internal peptides from the binding protein by Edman degradation, the corresponding ngcE gene, which encodes a predicted lipid-anchored protein, was identified by reverse genetics. Using a genomic phage library of S. olivaceoviridis genes encoding two other membrane proteins (named NgcF and NgcG) were identified adjacent to ngcE. Each of these is predicted to have six membrane-spanning helices and a consensus motif for integral membrane proteins characteristic of ABC transporters. In addition, the gene for a predicted regulator protein (NgcR) was detected. The ngcEFG operon lacks a gene for an ATP-hydrolysing protein. NgcE is a new member of the CUT-1 family of ABC transporters for carbohydrates. Comparative studies of the wild-type and a mutant strain carrying an insertion within the ngc operon clearly demonstrate that the Ngc system mediates the uptake of N-acetylglucosamine and chitobiose in vivo.

Recognition and degradation of chitin by streptomycetes

Chitin is the second most abundant renewable polysaccharide, as it is a component of the exoskeleton of many organisms and of the cell walls of numerous fungi. Most streptomycetes secrete a number of chitinases, hydrolyzing chitin to oligomers, chitobiose or N-acetylglucosamine which can be utilized as carbon or nitrogen source. The chitinases of several streptomycetes have been shown to have a modular arrangement comprising catalytic, substrate binding as well as linker domains. Moreover, during growth in the presence of chitin-containing substrates, many Streptomyces strains have been shown to secrete formerly unknown, small (about 200 aa) chitin binding proteins (CHBs) which lack enzymatic activity and specifically target and invade chitin. Several motifs, including the relative location and spacing of four tryptophan residues, are conserved in the investigated CHB types, CHB1 and CHB2. The affinity of CHB1 to crab shell chitin is two times higher than that of CHB2. Comparative studies of various generated mutant CHB1 proteins led to the conclusion that it is one of the exposed tryptophan residues that directly contributes to the interaction with chitin. On the basis of immunological, biochemical and physiological studies, it can be concluded that the CHBs act like a glue with which streptomycetes target chitin-containing samples or organisms. The ecological implications of these findings are discussed.

Mutations stabilizing an open conformation within the external region of the permeation pathway of the potassium channel KcsA

Four subunits of the bacterial Streptomyces lividans protein KcsA form a K+ channel which can be functionally reconstituted in vitro. Here we show that substitution of the tyrosine residue 82 by cysteine, valine or threonine, but not by glycine, led to functional channel types. Like the wild-type (WT) and an L81C channel, the mutant channels exhibit an internal pH-sensitive side and are cation selective. Based on the relative positions of the blocker tetraethylammonium within the electric field, the external entryways of the channels are concluded to have similar dimensions. For inward currents, the WT and the mutant channels vary in the occupancy of their subconductance states and concomitantly in their mean currents. Rectification properties are scarcely (L81C), little (Y82C) or considerably (Y82T and Y82V) altered. The data suggest that the amino acid type in position 82 stabilizes to varying degrees an open conformation within the external region of the permeation pathway.

Synthesis of the Streptomyces lividans maltodextrin ABC transporter depends on the presence of the regulator MalR

During growth with maltotriose or amylose, Streptomyces lividans and Streptomyces coelicolor A3(2) synthesize a maltodextrin uptake system with highest specificity for maltotriose. The transport activity is absent in mutants of S. coelicolor A3(2) lacking a functional MalE binding protein. Cloning and sequencing data suggest that the mal operon of S. coelicolor A3(2) corresponds to the one of S. lividans and that the deduced S. lividans Reg1 amino acid sequence is identical to that of MalR from S. coelicolor A3(2). It can be concluded that both strains have the same ABC transport system for maltodextrins. The S. lividans malR was cloned in Escherichia coli in frame with six histidine-encoding codons. The resulting, purified 6HisMalR(SI) was shown to bind to two motifs within the S. lividans malR-malE intergenic region and to dissociate in the presence of maltopentaose.

Characteristics of a Streptomyces coelicolor A3(2) extracellular protein targeting chitin and chitosan

Upstream of the Streptomyces coelicolor A3(2) chitinase G gene, a small gene (named chb3) is located whose deduced product shares 37% identical amino acids with the previously described CHB1 protein from Streptomyces olivaceoviridis. The chb3 gene and its upstream region were cloned in a multicopy vector and transformed into the plasmid-free Streptomyces lividans TK21 strain. The CHB3 protein (14.9 kDa) was secreted by the S. lividans TK21 transformant during growth in the presence of glucose, N-acetylglucosamine, yeast extract, and chitin. The protein was purified to homogeneity using anionic exchange, hydrophobic interaction chromatographies, and gel filtration. In contrast to CHB1, CHB3 targets alpha-chitin, beta-chitin, and chitosan at pH 6.0 but does so relatively loosely. The ecological implications of the divergence of substrate specificity of various types of chitin-binding proteins are described.

The DNA-binding characteristics of the Streptomyces reticuli regulator FurS depend on the redox state of its cysteine residues

Streptomyces reticuli produces a mycelium-associated enzyme (CpeB) which exhibits heme-dependent catalase and peroxidase activity, as well as heme-independent manganese-peroxidase activity. The cpeB gene does not have a promoter of its own. It is co-transcribed together with the adjacent furS gene from at least one promoter, the position of which was deduced on the basis of high-resolution S1 mapping of transcriptional start sites. Physiological and transcriptional studies suggested that FurS acts as a transcriptional repressor in the presence of Mn2+ and Fe2+ ions. A FurS fusion protein was purified, after cloning of the corresponding gene, either from Escherichia coli or Streptomyces lividans transformants. The fusion protein from each host strain can be converted into a form that exhibits reduced electrophoretic mobility following treatment with thiol-reducing agents; in the presence of diamide, in contrast, the mobility of the protein is enhanced. Additional immunological studies have shown that the native S. reticuli FurS also shows these properties, which are due to the presence of redox-sensitive cysteine residues. As revealed by gel-shift and in vitro footprinting studies, only the reduced form of the FurS fusion protein and the reduced FurS protein (partially purified from S. reticuli) is able to bind to a motif upstream of the furS gene. In the absence of first-row divalent ions, the binding site encompasses 22 bp. In the presence of Mn2+, Fe2+, Co2+, Cu2+ or Zn2+, however, the region bound is extended by 18 bp. It is noteworthy that the region upstream of the furA gene in several mycobacteria contains a very similar motif. The predicted mycobacterial FurA shares a high degree of sequence identity with FurS, and the furA gene is linked to one that encodes a catalase-peroxidase (KatG). The implications of these findings are discussed.

Efficient membrane assembly of the KcsA potassium channel in Escherichia coli requires the protonmotive force

Very little is known about the biogenesis and assembly of oligomeric membrane proteins. In this study, the biogenesis of KcsA, a prokaryotic homotetrameric potassium channel, is investigated. Using in vivo pulse-chase experiments, both the monomeric and tetrameric form could be identified. The conversion of monomers into a tetramer is found to be a highly efficient process that occurs in the Escherichia coli inner membrane. KcsA does not require ATP hydrolysis by SecA for insertion or tetramerization. The presence of the proton-motive force (pmf) is not necessary for transmembrane insertion of KcsA; however, the pmf proved to be essential for the efficiency of oligomerization. From in vivo and in vitro experiments it is concluded that the electrical component, deltapsi, is the main determinant for this effect. These results demonstrate a new role of the pmf in membrane protein biogenesis.

Solution structure and conformational changes of the Streptomyces chitin-binding protein (CHB1)

The shape and overall dimensions of the recently discovered Streptomyces alpha-chitin-binding protein, CHB1, were investigated by synchrotron radiation X-ray solution scattering. The radius of gyration and the maximum size of CHB1 were determined to be 1.75 +/- 0.03 nm and 6.0 +/- 0.2 nm, respectively. Using two independent ab initio approaches the low-resolution shape of the protein was found to consist of two domains, an elongated main globule with a length of about 4 nm and a foot-like domain of about 2 nm width. The structural and functional properties of CHB1 depend strongly on the presence of disulfide bonds; upon their reduction, the protein loses its affinity to chitin.

Binding characteristics of CebR, the regulator of the ceb operon required for cellobiose/cellotriose uptake in Streptomyces reticuli

The Streptomyces reticuli Avicelase (cellulase, Cell) hydrolyzes crystalline cellulose to cellooligomers, cellobiose and cellotriose which are taken up by mycelia via an ABC transport system (Ceb) induced during growth with cellobiose or cellulose. The cebR gene located upstream of the cebEFG operon was cloned in Escherichia coli in frame with six histidine-encoding codons. The resulting purified fusion protein was shown to bind to a motif of 23 bp, including a perfect 18-bp palindrome situated upstream of the cebEFG. Cytoplasmic extracts of induced, but not of uninduced S. reticuli protected the same DNA motif. Release of the CebR regulator from its operator occurs upon addition of cellopentaose which can be assumed to act as inducer within the mycelia.

Characteristics of chitin-binding proteins from Streptomycetes

During growth in the presence of chitin-containing substrates, many Streptomyces strains have been shown to secrete formerly unknown, small chitin-binding proteins (CHBs) which lack enzymatic activity, specifically target and invade, like a glue, alpha-chitin, but not beta-chitin or other polysaccharides. CHBs were purified, and their N-terminal amino acids were determined. Deduced oligonucleotides were used to identify the corresponding genes, which were then sequenced. The deduced CHB1 and CHB2 proteins contain 201 and 200 amino acids, respectively, 77.7% of which are identical. Several motifs, including the relative location and spacing of four tryptophan residues, are conserved in CHB1 and CHB2. The affinity of CHB1 to crab shell chitin is two times higher than that of CHB2. Comparative studies of various generated mutant CHB1 proteins led to the conclusion that mainly one of the exposed tryptophan residues directly contributed to the interaction with chitin. Using CHB doupled with FITC (fluoresceine isothiocyanate), a highly specific and rapid assay was developed to visualize the location of crystalline alpha-chitin within native samples by fluorescence or confocal laser microscopy. In contrast, the N-terminal domain (12 kDa) of the S. olivaceoviridis exochitinase can be used to detect alpha- and beta-chitin. The structural parameters inducing the recognition and possible loosening of alpha-chitin or of alpha- and beta-chitin are at present being investigated.

Architecture of the Streptomyces lividans DnaA protein-replication origin complexes

The Streptomyces oriC region contains two clusters of 19 DnaA boxes separated by a spacer (134 bp). The Streptomyces DnaA protein consists, like all other DnaA proteins, of four domains: domain III and the carboxyterminal part (domain IV) are responsible for binding of ATP and DNA, respectively. Binding of the DnaA protein to the entire oriC region analysed by electron microscopy showed that the DnaA protein forms separate complexes at each of the clusters of DnaA boxes, but not at the spacer separating them. In vivo mutational analysis revealed that the number of DnaA boxes and the presence of the spacer linking both groups of DnaA boxes seem to be important for a functional Streptomyces origin. We suggest that the arrangement of DnaA boxes allows the DNA-bound DnaA protein to induce bending and looping of the oriC region. As it was shown by electrophoretic mobility shift assay and "one hybrid system", two domains, I and III, facilitate interactions between DnaA molecules. We postulate that domain I and domain III could be involved in cooperativity at distant and at closely spaced DnaA boxes, respectively. The long domain II extends the range over which N termini (domain I) of DNA-bound DnaA protein can form dimers. Thus, interactions between DnaA molecules may bring two clusters of DnaA boxes separated by the spacer into functional contact by loop formation. Removal of the spacer region or deletion of domains I and II resulted, respectively, in nucleoprotein complexes which are not fully developed, or huge nucleoprotein aggregates.

The heme-independent manganese-peroxidase activity depends on the presence of the C-terminal domain within the Streptomyces reticuli catalase-peroxidase CpeB

Streptomyces reticuli produces a heme-containing homodimeric enzyme (160 kDa), the catalase-peroxidase CpeB, which is processed to the enzyme CpeC during prolonged growth. CpeC contains four subunits of 60 kDa each that do not include the C-terminal portion of the progenitor subunits. A genetically engineered cpeB gene encodes a truncated subunit lacking 195 of the C-terminal amino acids; four of these subunits assemble to form the enzyme CpeD. Heme binds most strongly in CpeB, least in CpeD. The catalase-peroxidase CpeB and its apo-form (obtained after extraction of heme) catalyze the peroxidation of Mn(II) to Mn(III), independent of the presence or absence of the heme inhibitor KCN. CpeC and CpeD, in contrast, do not exhibit manganese-peroxidase activity. The data show for the first time that a bacterial catalase-peroxidase has a heme-independent manganese-peroxidase activity, which depends on the presence of the C-terminal domain.

Pore mutations affecting tetrameric assembly and functioning of the potassium channel KcsA from Streptomyces lividans

Designed mutations within the Streptomyces lividans kcsA gene resulted in a set of mutant proteins, which were characterized in respect to their assembly and channel activities. (i) The amino acid residue leucine 81 located at the external side of KcsA was found to be exchangeable by a cysteine residue without affecting the channel characteristics. (ii) Substitution of the first glycine (G77) residue within the GYG motif by an alanine or substitution of the tyrosine (Y) residue 78 by a phenylalanine (F) led to mutant proteins which form tetramers of reduced stability. In contrast to the AYG mutant protein, GFG functions as an active K(+) channel whose characteristics correspond to those of the wild-type KcsA channel. (iii) The investigated mutant proteins, which carry different mutations (T72A, T72C, V76A, V76E, G77E, Y78A, G79A, G79D, G79E) within the signature sequence of the pore region, do not at all or only to a very small degree assemble as tetramers and lack channel activity.

Structure and regulation of the dnaA promoter region in three Streptomyces species

The regulatory region of the Streptomyces dnaA gene comprises a single promoter and two DnaA boxes that are located upstream of the promoter. Comparative analysis of the dnaA promoter region from S. chrysomallus, S. lividans and S. reticuli revealed that the location, spacing and orientation of the DnaA boxes are conserved. In vitro studies demonstrated that efficient binding of the Streptomyces DnaA protein to DNA requires the presence of two DnaA boxes. In vivo analysis of dnaA promoter mutants deleted for one or both DnaA boxes indicated that the dnaA gene is autoregulated. However, the degree of derepression observed is relatively modest.

Exploring the open pore of the potassium channel from Streptomyces lividans

The tetrameric potassium channel from Streptomyces lividans (KcsA) embedded in planar bilayers exhibits the following electrophysiological characteristics: (i) K+ ions can cross the pore in a highly hydrated state (nH2O > or = 6), (ii) the selectivity for K+ exceeds that for Na+ ions by 11 times, and both Ca2+ and Mg2+ are permeant, (iii) the internal side is blocked by Ba2+ ions in a voltage-dependent manner, (iv) intrinsic rectification is due to gating, depending on the direction of the electric field, (v) the internal side is pH-sensitive, and (vi) the open pore has a diameter of approximately 5.8 A. In conclusion, our results show that ion conduction and selectivity of KcsA cannot easily be reconciled with the properties deduced from the rigid crystal structure [Doyle et al., Science 280 (1998) 69-77], which must be concluded to have the pore trapped in its closed state.

Characterization of the binding protein-dependent cellobiose and cellotriose transport system of the cellulose degrader Streptomyces reticuli

Streptomyces reticuli has an inducible ATP-dependent uptake system specific for cellobiose and cellotriose. By reversed genetics a gene cluster encoding components of a binding protein-dependent cellobiose and cellotriose ABC transporter was cloned and sequenced. The deduced gene products comprise a regulatory protein (CebR), a cellobiose binding lipoprotein (CebE), two integral membrane proteins (CebF and CebG), and the NH2-terminal part of an intracellular beta-glucosidase (BglC). The gene for the ATP binding protein MsiK is not linked to the ceb operon. We have shown earlier that MsiK is part of two different ABC transport systems, one for maltose and one for cellobiose and cellotriose, in S. reticuli and Streptomyces lividans. Transcription of polycistronic cebEFG and bglC mRNAs is induced by cellobiose, whereas the cebR gene is transcribed independently. Immunological experiments showed that CebE is synthesized during growth with cellobiose and that MsiK is produced in the presence of several sugars at high or moderate levels. The described ABC transporter is the first one of its kind and is the only specific cellobiose/cellotriose uptake system of S. reticuli, since insertional inactivation of the cebE gene prevents high-affinity uptake of cellobiose.

Electron microscopy studies of cell-wall-anchored cellulose (Avicel)-binding protein (AbpS) from Streptomyces reticuli

Streptomyces reticuli produces a 35-kDa cellulose (Avicel)-binding protein (AbpS) which interacts strongly with crystalline cellulose but not with soluble types of cellulose. Antibodies that were highly specific for the NH2-terminal part of AbpS were isolated by using truncated AbpS proteins that differed in the length of the NH2 terminus. Using these antibodies for immunolabelling and investigations in which fluorescence, transmission electron, or immunofield scanning electron microscopy was used showed that the NH2 terminus of AbpS protrudes from the murein layer of S. reticuli. Additionally, inspection of ultrathin sections of the cell wall, as well as biochemical experiments performed with isolated murein, revealed that AbpS is tightly and very likely covalently linked to the polyglucane layer. As AbpS has also been found to be associated with protoplasts, we predicted that a COOH-terminal stretch consisting of 17 hydrophobic amino acids anchors the protein to the membrane. Different amounts of AbpS homologues of several Streptomyces strains were synthesized.

Interactions of the Streptomyces lividans initiator protein DnaA with its target

The Streptomyces lividans DnaA protein (73 kDa) consists, like other bacterial DnaA proteins, of four domains; it binds to 19 DnaA boxes in the complex oriC region. The S. lividans DnaA protein differs from others in that it contains an additional stretch of 120 predominantly acidic amino acids within domain II. Interactions between the DnaA protein and the two DnaA boxes derived from the promoter region of the S. lividans dnaA gene were analysed in vitro using three independent methods: Dnase-I-footprinting experiments, mobility-shift assay and surface plasmon resonance (SPR). The Dnase-I-footprinting analysis showed that the wild-type DnaA protein binds to both DnaA boxes. Thus, as in Escherichia coli and Bacillus subtilis, the S. lividans dnaA gene may be autoregulated. SPR analysis showed that the affinity of the DnaA protein for a DNA fragment containing both DnaA boxes from the dnaA promoter region (KD = 1.25 nM) is 10 times higher than its affinity for the single 'strong' DnaA box (KD = 12.0 nM). The mobility-shift assay suggests the presence of at least two classes of complex containing different numbers of bound DnaA molecules. The above data reveal that the DnaA protein binds to the two DnaA boxes in a cooperative manner. To deduce structural features of the Streptomyces domain II of DnaA protein, the amino acid DnaA sequences of three Streptomyces species were compared. However, according to the secondary structure prediction, Streptomyces domain II does not contain any common relevant secondary structural element(s). It can be assumed that domain II of DnaA protein can play a role as a flexible protein spacer between the N-terminal domain I and the highly conserved C-terminal part of DnaA protein containing ATP-binding domain III and DNA-binding domain IV.

Mercury resistance is encoded by transferable giant linear plasmids in two chesapeake bay Streptomyces strains

The Streptomyces strains CHR3 and CHR28, isolated from the Baltimore Inner Harbor, contained two and one, respectively, giant linear plasmids which carry terminally bound proteins. The plasmids pRJ3L (322 kb), from CHR3, and pRJ28 (330 kb), from CHR28, carry genes homologous to the previously characterized chromosomal Streptomyces lividans 66 operon encoding resistance against mercuric compounds. Both plasmids are transmissible (without any detectable rearrangement) to the chloramphenicol-resistant S. lividans TK24 strain lacking plasmids and carrying a chromosomal deletion of the mer operon. S. lividans TK24 conjugants harboring pRJ3L or pRJ28 exhibited profiles of mercury resistance to mercuric compounds similar to those of Streptomyces strains CHR3 and CHR28.

The cell wall-anchored Streptomyces reticuli avicel-binding protein (AbpS) and its gene

Streptomyces reticuli produces a 35-kDa cellulose-binding protein (AbpS) which interacts strongly with crystalline forms of cellulose (Avicel, bacterial microcrystalline cellulose, and tunicin cellulose); other polysaccharides are recognized on weakly (chitin and Valonia cellulose) or not at all (xylan, starch, and agar). The protein could be purified to homogeneity due to its affinity to Avicel. After we sequenced internal peptides, the corresponding gene was identified by reverse genetics. In vivo labelling experiments with fluorescein isothiocyanate (FITC), FITC-labelled secondary antibodies, or proteinase K treatment revealed that the anchored AbpS protrudes from the surfaces of the hyphae. When we investigated the hydrophobicity of the deduced AbpS, one putative transmembrane segment was predicted at the C terminus. By analysis of the secondary structure, a large centrally located alpha-helix which has weak homology to the tropomyosin protein family was found. Physiological studies showed that AbpS is synthesized during the late logarithmic phase, independently of the carbon source.

Specific interaction of the Streptomyces chitin-binding protein CHB1 with alpha-chitin--the role of individual tryptophan residues

Streptomyces olivaceoviridis secretes a so far unique protein of 18.7 kDa (CHB1) which lacks catalytic activity. It interacts highly specifically with alpha-chitin, but not with beta-chitin, chitosan, or cellulose. Each of the five codons for tryptophan (Trp) in the chb1 gene was replaced by those for leucine (Leu) or tyrosine (Tyr). Eight corresponding mutant proteins and the wild-type protein were purified to homogeneity and their binding capacity to alpha-chitin was determined. The relative affinities to anti-CHB1 antibodies, the kinetics of binding, the dissociation constants, circular dichroism, and fluorescence emission spectra for three mutant types were compared to the characteristics of CHB1. The presented data lead to the following conclusions. (a) CHBI presents a highly flexible protein lacking alpha-helices. (b) Replacement of each of the buried Trp residues (Trp134 and Trp184) leads to conformational alterations and, in due course, to a considerably reduced binding affinity of the protein. (c) The exchange of the exposed Trp 57 by either Leu or Tyr results in relatively slight topological changes, but entails a loss of binding capacity of about 90%. (d) The dissociation constant was highest for the mutant protein [L57]CHB1 (2.17 microM), followed by [L134]CHB1 (0.91 microM) and [L184]CHB1 (0.26 microM), and lowest for the progenitor CHB1 (0.11 microM), indicating its strong affinity to the unsoluble substrate. (e) The data suggest that the exposed Trp57 contributes directly and significantly to the interaction of CHB1 with alpha-chitin.

Purification and characterization of the Streptomyces lividans initiator protein DnaA

The Streptomyces lividans DnaA protein (73 kDa) consists, like the Escherichia coli DnaA protein (52 kDa), of four domains. The larger size of the S. lividans protein is due to an additional stretch of 120 predominantly acidic amino acids within domain II. The S. lividans protein was overproduced as a His-tagged fusion protein. The purified protein (isoelectric point, 5.7) has a weak ATPase activity. By DNase I footprinting studies, each of the 17 DnaA boxes (consensus sequence, TTGTCCACA) in the S. lividans oriC region was found to be protected by the DnaA fusion protein. Purified mutant proteins carrying a deletion of the C-terminally located helix-loop-helix (HLH) motif or with amino acid substitutions in helix A (L577G) or helix B (R595A) no longer interact with DnaA boxes. A substitution of basic amino acids in the loop of the HLH motif (R587A or R589A) entailed the formation of S. lividans mutant DnaA proteins with little or no capacity for binding to DnaA boxes. Thus, like in E. coli, the C-terminally located domain IV is absolutely necessary for the specific binding of DnaA. A mutant protein lacking a stretch of acidic amino acids corresponding to domain II is not affected in its DNA binding capacity. Whether the acidic domain II interacts with accessory proteins remains to be elucidated.

The Streptomyces ATP-binding component MsiK assists in cellobiose and maltose transport

Streptomyces reticuli harbors an msiK gene which encodes a protein with an amino acid identify of 90% to a corresponding protein previously identified in Streptomyces lividans. Immunological studies revealed that S. lividans and S. reticuli synthesize their highest levels of MsiK during growth with cellobiose, but not with glucose. Moreover, moderate amounts of MsiK are produced by both species in the course of growth with maltose, melibiose, and xylose and by S. lividans in the presence of xylobiose and raffinose. In contrast, a recently identified cellobiose-binding protein and its distantly related homolog were only found if S. reticuli or S. lividans, respectively, was cultivated with cellobiose. Uptake of cellobiose and maltose was tested and ascertained for S. reticuli and S. lividans, but not for an msiK S. lividans mutant. However, transformants of this mutant carrying the S. reticuli or S. lividans msiK gene on a multicopy plasmid had regained the ability to transport both sugars. The data show that MsiK assists two ABC transport systems.

A lipid-anchored binding protein is a component of an ATP-dependent cellobiose/cellotriose-transport system from the cellulose degrader Streptomyces reticuli

During cultivation in the presence of cellobiose or crystalline cellulose, Streptomyces reticuli expresses an inducible uptake system that transports cellobiose (K(m), 4 microM), cellotriose and, to a lesser degree, cellotetraose and cellopentaose. Cellobiose uptake is dependent on ATP and inhibited by N-ethylmaleimide. A binding protein was identified in its palmitylated form in the cytoplasmic membrane of mycelia. It could be extracted with the detergent Triton X-100 and purified by two subsequent anion-exchange chromatographies. It showed highest affinity (Kd, 1.5 microM) for cellobiose and cellotriose. The data suggest that cellobiose/cellotriose uptake is mediated by a membrane-anchored lipoprotein as a component of an ATP-binding-cassette-transporter system.

The synthesis of the Streptomyces reticuli cellulase (avicelase) is regulated by both activation and repression mechanisms

The Streptomyces reticuli cellulase (Cell, Avicelase) hydrolyzes crystalline cellulose (Avicel) efficiently to cellobiose. The synthesis of the enzyme is induced by Avicel and repressed by glucose. DNA-binding proteins were purified from induced S. reticuli mycelia by affinity chromatography using the upstream region of the cell gene linked to Sepharose. The enriched protein(s) provoked a gel electrophoresis mobility shift of the upstream region, irrespective of the presence or absence of a 14-bp palindromic sequence, and enhanced the transcription of the cell gene by the S. reticuli RNA polymerase in vitro. The binding site (GTGACTGAGCGCCG) for the protein(s) was located in the vicinity of a DNA bend upstream of the transcriptional start site. Results of physiological studies, deletion and gel-shift analyses lead to the conclusion that a 14-bp palindrome (TGGGAGCGCTCCCA)--situated between the transcriptional start site and the structure gene--is the operator for a repressor protein. The data presented suggest that the two identified cis-acting elements, in cooperation with an activator and a repressor, mediate regulation of cell transcription.

Production and processing of a 59-kilodalton exochitinase during growth of Streptomyces lividans carrying pCHIO12 in soil microcosms amended with crab or fungal chitin

Streptomyces lividans (pCHIO12), which carries the previously cloned Streptomyces olivaceoviridis exo-chiO1 gene on a multicopy vector, secretes a 59-kDa exochitinase, consisting of a catalytic domain (40 kDa), a central fibronectin type III-like module, and a chitin-binding domain (12 kDa). The propagation rate of S. lividans (pCHIO12) was higher in soil microcosms amended with fungal mycelia than in those containing crab chitin. Comparative biochemical and immunological studies allowed the following conclusions to be drawn. Within soil microcosm systems amended with crab shell chitin or chitin-containing Aspergillus proliferans mycelia, the strain expressed the clones exo-chiO1 gene and produced high quantities of a 59-kDa exochitinase. The enzyme was preferentially attached via its binding domain to the pellet from soil or liquid cultures. In contrast, truncated forms of 47, 40, and 25 kDa could be easily extracted from soil. The relative proportions of the 59-kDa enzyme and its truncated forms varied depending on the source of chitin and differed in soil and in liquid cultures.

The cellulolytic system of Streptomyces reticuli

The bacterium Streptomyces reticuli produces an unusual mycelia-associated cellulase (Avicelase, Cel1) which is solely sufficient to degrade crystalline cellulose to cellobiose. The enzyme consists of a binding domain, one adjoining region with unknown function, and a catalytic domain belonging to the cellulase family E. During cultivation, the strain produces a specific protease which processes the Avicelase to a truncated enzyme lacking the binding domain. The cellulase synthesis is regulated by induction (Avicel) and repression (metabolizable sugars and glycerol).

Visualization of alpha-chitin with a specific chitin-binding protein (CHB1) from Streptomyces olivaceoviridis

Recently we identified a so far unique protein (CHB1) which interacts specifically with crystalline alpha-chitin. Having optimized the binding conditions for CHB1 coupled with fluorescein isothiocyanate (FITC), we succeeded in developing a highly sensitive assay to detect alpha-chitin. CHB1-FITC interacted neither with beta- or colloidal chitin nor with chitooligomers or cellulose. With the help of fluorescence or confocal laser microscopy, the relative location of crystalline alpha-chitin within various native samples of fungi and other organisms can be clearly and rapidly visualized.

A prokaryotic potassium ion channel with two predicted transmembrane segments from Streptomyces lividans

We report the identification, functional expression, purification, reconstitution and electrophysiological characterization of an up to now unique prokaryotic potassium ion channel (KcsA). It has a rectifying current-voltage relationship and displays subconductance states, the largest of which amounts to A approximately equal to 90 pS. The channel is blocked by Cs- ions and gating requires the presence of Mg2+ ions. The kcsA gene has been identified in the gram-positive soil bacterium Streptomyces lividans. It encodes a predicted 17.6 kDa protein with two potential membrane-spanning helices linked by a central domain which shares a high degree of similarity with the H5 segment conserved among eukaryotic ion channels. Multiple alignments of deduced amino acids suggest that the novel channel has the closest kinship to the S5, H5 and S6 regions of voltage-gated K+ channel families, mainly to the subfamily represented by the Shaker protein from Drosophila melanogaster. Moreover, KcsA is most distantly related to eukaryotic inwardly rectifying channels with two putative predicted transmembrane segments.

Identification of a methyl-specific restriction system mediated by a conjugative element from Streptomyces bambergiensis

pBL2 was identified genetically but not physically in Streptomyces lividans after its mating with S. bambergiensis. During conjugation, pBL2 was transferred at high frequency to S. lividans and S. coelicolor. pBL2.1 DNA isolated from S. coelicolor exconjugants as a circular plasmid was shown to derive from the genome of S. bambergiensis. S. lividans carrying pBL2 or pBL2.1 acquired a methyl-specific restriction (MsrA+) phenotype. The corresponding enzyme was partially purified and shown to resemble a class II endonuclease which cleaves Dam-methylated DNA preferentially.

Minimal requirements of the Streptomyces lividans 66 oriC region and its transcriptional and translational activities

Deletion analysis of a previously constructed minichromosome revealed that a stretch of DNA which is longer than 623 bp but shorter than 837 bp is required for autonomous replication of the Streptomyces lividans chromosome. Each of the dnaA and dnaN genes flanking the oriC region is individually transcribed from two promoters. Within the intergenic, nontranslatable region between the dnaA and dnaN genes, five main transcripts and several less abundant transcripts of various lengths as well as one of the promoters were identified. The introduction of additional DnaA boxes in S. lividans led to a significant increase in dnaA gene transcripts and to an enhanced level of the DnaA (73-kDa) protein. In summary, the data suggest that dnaA gene transcription is autoregulated and that initiation of the S. lividans chromosome is tightly controlled.

Binding and substrate specificities of a Streptomyces olivaceoviridis chitinase in comparison with its proteolytically processed form

Streptomyces olivaceoviridis is an efficient chitin degrader. One of its genes encoding an exochitinase (exo-ChiO1) was previously characterized. The transcription was found to be inducible by chitin, but not by glucose. The transcriptional start site is situated 38 bp upstream of the start codon. S. olivaceoviridis as well as transformants of S. vinaceus and S. lividans carrying the exo-chiO1 gene on a multicopy vector secrete a 59-kDa chitinase which adheres strongly and under most conditions irreversibly to the substrate chitin. After having released the enzyme from the crystalline substrate in the presence of high concentrations of guanidine hydrochloride, it was purified to homogeneity by consecutive chitin- and immunoaffinity chromatographies. Immunofluorescence microscopy revealed that the enzyme specifically binds to crystalline alpha-chitin within fungi and other organisms as well as to beta-chitin, but not to colloidal chitin, chitosan, various types of cellulose, or other polysaccharides. The amino acids deduced from the highly specific binding domain (12 kDa) of this enzyme do not share significant similarity with any known region interacting with chitin or another substrate. During cultivation with chitin, the 59-kDa enzyme is proteolytically processed to a 47-kDa truncated chitinase lacking the chitin-binding domain. The 47-kDa enzyme hydrolyses crystalline chitin considerably less efficiently than the 59-kDa enzyme, whereas colloidal chitin and low-molecular-mass substrates are quite equally degraded by both enzymes at identical optimal pH (7.3) and temperature (45-55 degrees C) values. Thus a strong adhesion of the enzyme to its crystalline substrate via its binding domain is a prerequisite for efficient hydrolysis.

Studies of Streptomyces reticuli cel-1 (cellulase) gene expression in Streptomyces strains, Escherichia coli, and Bacillus subtilis

Various streptomyces strains [Streptomyces lividans 66, Streptomyces vinaceus, and Strepotmyces coelicolor A3 (2)] acquired the ability to utilize crystalline cellulose (Avicel) after transformation with a multicopy vector containing the cel-1 gene from Streptomyces reticuli. The expression level in these hosts was two to three times lower than in S. reticuli, indicating the absence of positive regulatory elements. Like S. reticuli, they processed the Avicelase to its catalytic domain and to an enzymatically inactive part. The cel-1 gene with its original upstream region was not expressed within Escherichia coli. When cel-1 had been fused in phase with the lacZ gene, large quantities of the fusion protein were produced in E. coli. However, this protein was enzymatically inactive and proteolytically degraded to a series of truncated forms. As the cellulase (Avicelase) synthesized by S. reticuli is not cleaved by the E. coli proteases, its posttranslational modification is proposed. With Bacillus subtilis as host, the cel-1 gene was expressed neither under its own promoter nor under the control of a strong Bacillus promoter.

Purification and characterization of a novel extracellular Streptomyces lividans 66 enzyme inactivating fusidic acid

The wild-type strain Streptomyces lividans 66 is resistant against the steroid-like antibiotic fusidic acid. Comparative studies of the wild-type strain and a fusidic acid-sensitive mutant allowed the identification of an extracellular enzyme which inactivates fusidic acid. With the help of a combination of ultrafiltration and chromatographies with Phenyl-Sepharose and an anion exchanger, the enzyme was highly purified. Its apparent molecular mass is 48 kDa, its optimal activity ranges between 45 and 55 degrees C, and its optimal pH is 6.0 to 9.0. It is stimulated by neither monovalent nor divalent ions. The enzyme acts as a specific esterase which removes the acetyl group at C-16 from fusidic acid. The resulting intermediate is unstable, and spontaneous lactonization between C-21 and C-16 occurs rapidly.

The novel lectin-like protein CHB1 is encoded by a chitin-inducible Streptomyces olivaceoviridis gene and binds specifically to crystalline alpha-chitin of fungi and other organisms

The chb1 gene, which encodes the unique lectin-like alpha-chitin-binding protein CHB1 of Streptomyces olivaceoviridis, was cloned. Transformants of Streptomyces lividans harbouring the plasmid pCHB10 overproduced the extracellular CHB1 protein; the protein showed neither enzymatic nor antifungal activity. Biochemical analyses and immunofluorescence microscopy indicated that CHB1 binds strongly to alpha-chitin, but neither to chitosan and beta-chitin, nor to various types of cellulose. Within hyphae of fungi, the relative location of crystalline chitin was visualized with fluorescein-labelled CHB1. These studies suggest that the new protein could serve as a tool to identify alpha-chitin within different organisms. The chb1 gene consists of a reading frame of 603 bp and its transcription occurred only if the Streptomyces strain was cultivated with chitin as the sole carbon source. The deduced mature CHB1 protein (18.7 kDa) shows no apparent similarity to any known protein. Within a region containing 100 residues of the deduced CHB1 protein, four tryptophan and two asparagine residues as well as one glycine and one cysteine residue were identified, the relative positions of which are analogous to those of several cellulose-binding domains of bacterial glycohydrolases. The results of spectroscopical studies suggest a possible involvement of tryptophan residues in the interaction of CHB1 with alpha-chitin.

The linear Streptomyces plasmid pBL1: analyses of transfer functions

pBL1 is a conjugative linear extrachromosomal element of 43 kb previously isolated after interspecific mating between Streptomyces bambergiensis and S. lividans. Cloning experiments using the non-conjugative, circular Streptomyces vector pIJ702 allowed the identification of a 5.74 kb region from pBL1 which facilitates plasmid transfer. Insertion and deletion mutagenesis, gene disruptions, and sequence data suggest that at least five previously unknown genes of pBL1 are required for efficient plasmid transfer and its regulation.

Inducible transcription of the dnaA gene from Streptomyces lividans 66

The dnaA gene of Streptomyces lividans was cloned using the Escherichia coli medium-copy-number vector pSU18 and E. coli strain TC1963, which can by-pass the requirement for the DnaA protein. Its regulatory region was subcloned in the Streptomyces probe vector pIJ4083. Primer extension and S1 mapping studies allowed the identification of a class I Streptomyces promotor (P2). An additional, previously unknown promoter type (P1) was found by S1 mapping. The presence of two DnaA box motifs between P1 and P2 suggests that the transcriptions of the S. lividans dnaA gene is autoregulated by its gene product. It was shown that the transcription of the dnaA gene is significantly induced by mitomycin C, an agent known to inhibit DNA replication. The data suggest that, as in E. coli, one of the regulatory mechanisms governing the transcription of the dnaA gene in S. lividans is probably related to the SOS response network.

Characteristics of an exochitinase from Streptomyces olivaceoviridis, its corresponding gene, putative protein domains and relationship to other chitinases

Streptomyces olivaceoviridis efficiently degrades chitin. Shotgun cloning of partially Sau3A-cleaved DNA using the multicopy vector pIJ702 and Streptomyces lividans 66 as host resulted in the identification of the plasmid pCHI O1 which harbours an insert of 4.6 kb. In the presence of chitin as sole carbon source, transformants of S. lividans 66 carrying pCHI O1 or its derivatives with smaller inserts overproduced an exochitinase which was purified to homogeneity. The chitin-inducible enzyme with an isoelectric point of 4.0 shows optimal activity at pH 7.3 and 55 degrees C, has an apparent molecular mass of 47 kDa and is competitively inhibited by the pseudosugar allosamidin. The enzyme was identified as an exochitinase since it generates exclusively chitobiose from chitotetraose, chitohexaose, and colloidal high-molecular mass chitin. Sequence analysis of a reading frame of 1794 base pairs and comparison of the deduced amino-acid sequence allowed the identification of the putative catalytic domain, one region with significant similarity to the type-III module of fibronectin and one domain of unknown function. Multiple sequence alignment and hydrophobic-cluster analysis of 25 chitinolytic enzymes from bacteria, fungi and plants allowed the identification of their characteristic domains. The exochitinase from S. olivaceoviridis shares highest similarity with the chitinase D from Bacillus circulans.

Biochemical Characterization of a Protease Involved in the Processing of a Streptomyces reticuli Cellulase (Avicelase)

A 36-kDa protease from Streptomyces reticuli had recently been shown to be responsible for the in vivo and in vitro processing of the 82-kDa cellulase (Avicelase) Cel-1 from S. reticuli to a 42-kDa truncated enzyme. It was induced only in the presence of Avicel, hydroxyethylcellulose, and xylan. The addition of the nonionic detergent Tween 80 to the culture medium containing Avicel as the carbon source led to a 10-fold increase in extracellular proteolytic activity. The protease, which has an isoelectric point of 3.9, was purified to homogeneity from the culture filtrate by a combination of anion-exchange and hydrophobic-interaction chromatographies and was characterized biochemically. The enzyme hydrolyzed gelatin and the chromogenic substrates Azocoll, Azocasein, and Azoalbumin. Its highest activity was determined between pH 7.0 and 7.7 and at 55°C. The proteolytic activity was inhibited by 1,10-phenanthroline and EDTA; however, no metal ions were detected to be associated with the protein. The protease was stable in the presence of 1 M urea and 0.01 M sodium dodecyl sulfate. The inhibitory effect of alpha-2-macroglobulin indicated an endo-mode of proteolytic cleavage. Studies with lectins and sugar analysis by mass spectroscopy indicated that the cellulase (Avicelase) Cel-1 was neither N nor O glycosylated. Its processing by the protease occurred at temperatures ranging from 30 to 55°C, pH 7.5, in the presence of 2 mM dithiothreitol.

The gene encoding the cellulase (Avicelase) Cel1 from Streptomyces reticuli and analysis of protein domains

Streptomyces reticuli produces an unusual cellulase (Avicelase), with an apparent molecular weight of 82 kDa, which is solely sufficient to degrade crystalline cellulose. During cultivation the processing of the Avicelase to a truncated enzyme (42 kDa) and an inactive protein (40 kDa) correlated with the occurrence of an extracellular protease. After its purification this 36 kDa protease cleaved the S. reticuli Avicelase in vitro in the same manner. Using antibodies raised against the Avicelase and its truncated form (42 kDa) and gene libraries of S. reticuli DNA in the Escherichia coli phage vectors lambda gt11 and Charon 35, the Avicelase gene (cel1) was identified. Further subcloning and DNA-sequencing revealed a G+C rich (72%) reading frame of 2238 bp encoding a protein of 746 amino acids. The transcriptional start site was mapped about 180 bp upstream from the GTG start codon. A signal sequence of 29 amino acids was identified by aligning the deduced amino acids with the characterized N-terminus of the 82 kDa Avicelase. Comparison of the N-terminal amino acids from the purified proteins with the amino acid sequence derived from the Avicelase gene revealed that the truncated enzyme (42 kDa) corresponds to the C-terminal region whereas the inactive proteolytically derived protein (40 kDa) represents the N-terminal part of the 82 kDa Avicelase. Comparisons with amino acid sequences deduced from known cellulase genes indicated the presence of three putative protein domains: (i) an N-terminal part showing significant similarity with a repeat region of endoglucanase C from Cellulomonas fimi, recently shown to be a cellulose-binding domain; (ii) an adjoining region sharing homology with the N-terminal domains with unknown function of endoglucanase A from Pseudomonas fluorescens, endoglucanase D from Clostridium thermocellum and a cellodextrinase from Butyrivibrio fibrisolvens, and (iii) a C-terminal catalytic domain belonging to cellulase family E.

Diversity among Streptomyces Strains Causing Potato Scab

Eighty Streptomyces isolates, including 35 potato scab-inducing strains and 12 reference strains of Streptomyces scabies , were physiologically characterized by a total of 329 miniaturized tests. Overall similarities of all strains were determined by numerical taxonomy, with the unweighted average linkage (UPGMA) algorithm and simple matching ( S sm ) and Jaccard ( S j ) coefficients used as measures for similarity. Three cluster groups (A to C) were defined at a similarity level of 80.1% ( S sm ); these groups contained 14 clusters and 24 unclustered strains defined at a similarity level of 86.5% ( S sm ). Cluster group A contained strains phenotypically related to S. griseus or S. exfoliatus , whereas cluster group B contained strains which were phenotypically related to S. violaceus or S. rochei . The majority of the pathogenic isolates and reference strains were assigned to S. violaceus (57%) and S. griseus (22%). A DNA probe derived from the rRNA operon of S. coelicolor IMET 40271 was used to detect restriction fragment length polymorphisms (RELPs) among 40 pathogenic and nonpathogenic Streptomyces isolates. Southern blots revealed a high degree of diversity among the pathogenic strains tested. No significant correlation between numerical classification and RFLP grouping of Streptomyces strains could be revealed. The results obtained suggest that RFLP data are of minor importance in classification of Streptomyces species and that genes for pathogenicity determinants are spread among different Streptomyces species by mobilizable elements.