Localization of myxobacterial hemagglutinin in the periplasmic space and on the cell surface of Myxococcus xanthus during developmental aggregation

High-Mannose Specific Lectin and Its Recombinants from a Carrageenophyta Kappaphycus alvarezii Represent a Potent Anti-HIV Activity Through High-Affinity Binding to the Viral Envelope Glycoprotein gp120

We previously reported that a high-mannose binding lectin KAA-2 from the red alga Kappaphycus alvarezii, which is an economically important species and widely cultivated as a source of carrageenans, had a potent anti-influenza virus activity. In this study, the full-length sequences of two KAA isoforms, KAA-1 and KAA-2, were elucidated by a combination of peptide mapping and cDNA cloning. They consisted of four internal tandem-repeated domains, which are conserved in high-mannose specific lectins from lower organisms, including a cyanobacterium Oscillatoria agardhii and a red alga Eucheuma serra. Using an Escherichia coli expression system, an active recombinant form of KAA-1 (His-tagged rKAA-1) was successfully generated in the yield of 115 mg per a litter of culture. In a detailed oligosaccharide binding analysis by a centrifugal ultrafiltration-HPLC method with 27 pyridylaminated oligosaccharides, His-tagged rKAA-1 and rKAA-1 specifically bound to high-mannose N-glycans with an exposed α1-3 mannose in the D2 arm as the native lectin did. Predicted from oligosaccharide-binding specificity, a surface plasmon resonance analysis revealed that the recombinants exhibit strong interaction with gp120, a heavily glycosylated envelope glycoprotein of HIV with high association constants (1.48-1.61 × 10(9) M(-1)). Native KAAs and the recombinants inhibited the HIV-1 entry at IC50s of low nanomolar levels (7.3-12.9 nM). Thus, the recombinant proteins would be useful as antiviral reagents targeting the viral surface glycoproteins with high-mannose N-glycans, and the cultivated alga K. alvarezii could also be a good source of not only carrageenans but also this functional lectin(s).

High-Mannose Specific Lectin and Its Recombinants from a Carrageenophyta Kappaphycus alvarezii Represent a Potent Anti-HIV Activity Through High-Affinity Binding to the Viral Envelope Glycoprotein gp120

We previously reported that a high-mannose binding lectin KAA-2 from the red alga Kappaphycus alvarezii, which is an economically important species and widely cultivated as a source of carrageenans, had a potent anti-influenza virus activity. In this study, the full-length sequences of two KAA isoforms, KAA-1 and KAA-2, were elucidated by a combination of peptide mapping and complementary DNA (cDNA) cloning. They consisted of four internal tandem-repeated domains, which are conserved in high-mannose specific lectins from lower organisms, including a cyanobacterium Oscillatoria agardhii and a red alga Eucheuma serra. Using an Escherichia coli expression system, an active recombinant form of KAA-1 (His-tagged rKAA-1) was successfully generated in the yield of 115 mg per liter of culture. In a detailed oligosaccharide binding analysis by a centrifugal ultrafiltration-HPLC method with 27 pyridylaminated oligosaccharides, His-tagged rKAA-1 and rKAA-1 specifically bound to high-mannose N-glycans with an exposed α1-3 mannose in the D2 arm as the native lectin did. Predicted from oligosaccharide binding specificity, a surface plasmon resonance analysis revealed that the recombinants exhibit strong interaction with gp120, a heavily glycosylated envelope glycoprotein of HIV with high association constants (1.48 - 1.61 × 10(9) M(-1)). Native KAAs and the recombinants inhibited the HIV-1 entry at IC50s of low nanomolar levels (7.3-12.9 nM). Thus, the recombinant proteins would be useful as antiviral reagents targeting the viral surface glycoproteins with high-mannose N-glycans, and the cultivated alga K. alvarezii could also be a good source of not only carrageenans but also this functional lectin(s).

A multi-protein complex from Myxococcus xanthus required for bacterial gliding motility

Myxococcus xanthus moves by gliding motility powered by Type IV pili (S-motility) and a second motility system, A-motility, whose mechanism remains elusive despite the identification of approximately 40 A-motility genes. In this study, we used biochemistry and cell biology analyses to identify multi-protein complexes associated with A-motility. Previously, we showed that the N-terminal domain of FrzCD, the receptor for the frizzy chemosensory pathway, interacts with two A-motility proteins, AglZ and AgmU. Here we characterized AgmU, a protein that localized to both the periplasm and cytoplasm. On firm surfaces, AgmU-mCherry colocalized with AglZ as distributed clusters that remained fixed with respect to the substratum as cells moved forward. Cluster formation was favoured by hard surfaces where A-motility is favoured. In contrast, AgmU-mCherry clusters were not observed on soft agar surfaces or when cells were in large groups, conditions that favour S-motility. Using glutathione-S-transferase affinity chromatography, AgmU was found to interact either directly or indirectly with multiple A-motility proteins including AglZ, AglT, AgmK, AgmX, AglW and CglB. These proteins, important for the correct localization of AgmU and AglZ, appear to be organized as a motility complex, spanning the cytoplasm, inner membrane and the periplasm. Identification of this complex may be important for uncovering the mechanism of A-motility.

Primary structure and carbohydrate binding specificity of a potent anti-HIV lectin isolated from the filamentous cyanobacterium Oscillatoria agardhii

The primary structure of a lectin, designated Oscillatoria agardhii agglutinin (OAA), isolated from the freshwater cyanobacterium O. agardhii NIES-204 was determined by the combination of Edman degradation and electron spray ionization-mass spectrometry. OAA is a polypeptide (Mr 13,925) consisting of two tandem repeats. Interestingly, each repeat sequence of OAA showed a high degree of similarity to those of a myxobacterium, Myxococcus xanthus hemagglutinin, and a marine red alga Eucheuma serra lectin. A systematic binding assay with pyridylaminated oligosaccharides revealed that OAA exclusively binds to high mannose (HM)-type N-glycans but not to other N-glycans, including complex types, hybrid types, and the pentasaccharide core or oligosaccharides from glycolipids. OAA did not interact with any of free mono- and oligomannoses that are constituents of the branched oligomannosides. These results suggest that the core disaccharide, GlcNAc-GlcNAc, is also essential for binding to OAA. The binding activity of OAA to HM type N-glycans was dramatically decreased when alpha1-2 Man was attached to alpha1-3 Man branched from the alpha1-6 Man of the pentasaccharide core. This specificity of OAA for HM-type oligosaccharides is distinct from other HM-binding lectins. Kinetic analysis with an HM heptasaccharide revealed that OAA possesses two carbohydrate binding sites per molecule, with an association constant of 2.41x10(8) m-1. Furthermore, OAA potently inhibits human immunodeficiency virus replication in MT-4 cells (EC50=44.5 nm). Thus, we have found a novel lectin family sharing similar structure and carbohydrate binding specificity among bacteria, cyanobacteria, and marine algae.

Pattern formation: fruiting body morphogenesis in Myxococcus xanthus

When Myxococcus xanthus cells are exposed to starvation, they respond with dramatic behavioral changes. The expansive swarming behavior stops and the cells begin to aggregate into multicellular fruiting bodies. The cell-surface-associated C-signal has been identified as the signal that induces aggregation. Recently, several of the components in the C-signal transduction pathway have been identified and behavioral analyses are beginning to reveal how the C-signal modulates cell behavior. Together, these findings provide a framework for understanding how a cell-surface-associated morphogen induces pattern formation.

Pirellulosomes: a new type of membrane-bounded cell compartment in planctomycete bacteria of the genus Pirellula

A distinct type of cellular organization was found in two species of the planctomycete genus Pirellula, Pirellula marina and Pirellula staleyi. Both species possess two distinct regions within the cell which are separated by a single membrane. The major region of the cell, the pirellulosome, contains the fibrillar condensed nucleoid. The other area, the polar cap region, forms a continuous layer surrounding the entire pirellulosome and displays a cap of asymmetrically distributed material at one cell pole. Immuno- and cytochemical-labelling of P. marina demonstrated that DNA is located exclusively within the pirellulosome; cell RNA is concentrated in the pirellulosome, with some RNA also located in the polar cap region.

Fungal galectins, sequence and specificity of two isolectins from Coprinus cinereus

Galectins are members of a genetically related family of beta-galactoside-binding lectins. At least eight distinct mammalian galectins have been identified. More distantly related, but still conserving amino acid residues critical for carbohydrate-binding, are galectins in chicken, eel, frog, nematode, and sponge. Here we report that galectins are also expressed in a species of fungus, the inky cap mushroom, Coprinus cinereus. Two dimeric galectins are expressed during fruiting body formation which are 83% identical to each other in amino acid sequence and conserve all key residues shared by members of the galectin family. Unlike most galectins, these have no N-terminal post-translational modification and no cysteine residues. We expressed one of these as a recombinant protein and studied its carbohydrate-binding specificity using a novel nonradioactive assay. Binding specificity has been well studied for a number of other galectins, and like many of these, the recombinant C. cinereus galectin shows particular affinity for blood group A structures. These results demonstrate not only that the galectin gene family is evolutionarily much older than previously realized but also that fine specificity for complex saccharide structures has been conserved. Such conservation implies that galectins evolved to perform very basic cellular functions, presumably by interaction with glycoconjugates bearing complex lactoside carbohydrates resembling blood group A.

NMR-derived three-dimensional solution structure of protein S complexed with calcium

BACKGROUND

Protein S is a developmentally-regulated Ca(2+)-binding protein of the soil bacterium Myxococcus xanthus. It functions by forming protective, multilayer spore surface assemblies which may additionally act as a cell-cell adhesive. Protein S is evolutionarily related to vertebrate lens beta gamma-crystallins.

RESULTS

The three-dimensional solution structure of Ca(2+)-loaded protein S has been determined using multi-dimensional heteronuclear NMR spectroscopy. (Sixty structures were calculated, from which thirty were selected with a root mean square difference from the mean of 0.38 A for backbone atoms and 1.22 A for all non-hydrogen atoms.) The structure was analyzed and compared in detail with X-ray crystallographic structures of beta gamma-crystallins. The two internally homologous domains of protein S were compared, and hydrophobic cores, domain interfaces, surface ion pairing, amino-aromatic interactions and potential modes of multimerization are discussed.

CONCLUSIONS

Structural features of protein S described here help to explain its overall thermostability, as well as the higher stability and Ca2+ affinity of the amino-terminal domain relative to the carboxy-terminal domain. Two potential modes of multimerization are proposed involving cross-linking of protein S molecules through surface Ca(2+)-binding sites and formation of the intramolecular protein S or gamma B-crystallin interdomain interface in an intermolecular content. This structural analysis may also have implications for Ca(2+)-dependent cell-cell interactions mediated by the vertebrate cadherins and Dictyostelium discoideum protein gp24.

Polarized cells, polar actions

The recognition of polar bacterial organization is just emerging. The examples of polar localization given here are from a variety of bacterial species and concern a disparate array of cellular functions. A number of well-characterized instances of polar localization of bacterial proteins, including the chemoreceptor complex in both C. crescentus and E. coli, the maltose-binding protein in E. coli, the B. japonicum surface attachment proteins, and the actin tail of L. monocytogenes within a mammalian cell, involve proteins or protein complexes that facilitate bacterial interaction with the environment, either the extracellular milieux or that within a plant or mammalian host. The significance of this observation remains unclear. Polarity in bacteria poses many problems, including the necessity for a mechanism for asymmetrically distributing proteins as well as a mechanism by which polar localization is maintained. Large structures, such as a flagellum, are anchored at the pole by means of the basal body that traverses the peptidoglycan wall. But for proteins and small complexes, whether in the periplasm or the membrane, one must invoke a mechanism that prevents the diffusion of these proteins away from the cell pole. Perhaps the periplasmic proteins are retained at the pole by the presence of the periseptal annulus (35). The constraining features for membrane components are not known. For large aggregates, such as the clusters of MCP, CheA, and CheW complexes, perhaps the size of the aggregate alone prevents displacement. In most cases of cellular asymmetry, bacteria are able to discriminate between the new pole and the old pole and to utilize this information for localization specificity. The maturation of new pole to old pole appears to be a common theme as well. Given numerous examples reported thus far, we propose that bacterial polarity displays specific rules and is a more general phenomenon than has been previously recognized.

Determinants of an unusually stable mRNA in the bacterium Myxococcus xanthus

Myxococcus xanthus is a Gram-negative bacterium which has a complex life cycle that includes development (fruiting body formation). The gene for myxobacterial haemagglutinin, mbhA, is developmentally regulated and highly expressed. In this report we show that the mbhA mRNA is exceptionally stable for a prokaryotic organism, exhibiting a chemical half life (t1/2) of 150 min at 18 h of development. The mbhA mRNA was not stable in vegetatively growing cells nor was it stable when expressed in Escherichia coli. We have used site-directed mutagenesis of the mbhA gene to analyse some of the determinants which mediate the stability of the mbhA transcript. Sequences within the 3'-untranslated region (3'-UTR) were found to be crucial for mRNA stability. This region of mRNA can potentially form an extremely stable stem-loop structure immediately adjacent to the translational stop codon. A deletion within this region caused a 10-fold increase in the decay rate of the transcript. Furthermore, conditions which were associated with reduced mbhA translation or mutations that caused premature termination of translation drastically reduced mRNA stability even in the presence of the wild type 3'-UTR. These results suggest that a significant aspect of mbhA mRNA stability involves a synergistic interaction of the translational machinery with sequence elements within the 3'-UTR.

Release of a cell surface protein during development of Myxococcus xanthus

VGP is a major cell-surface glycoprotein present in vegetative cells of Myxococcus xanthus. Serological assays indicated that this protein was released from cells and accumulated in the medium during development, i.e., aggregation, fruiting body formation, and myxosporulation. Cells induced to form spores in the absence of aggregation retained VGP, indicating that loss of VGP was associated with developmental aggregation rather than myxosporulation. Anti-VGP antibodies inhibited vegetative cell gliding, suggesting the protein may also be required for motility.

Development in Myxococcus xanthus involves differentiation into two cell types, peripheral rods and spores

Myxococcus xanthus, a gram-negative bacterium, has a complex life cycle. In response to starvation, most cells in a population participate in the formation of multicellular aggregates (i.e., fruiting bodies) in which cells differentiate into spores. However, some cells do not enter aggregates. In this and the two accompanying reports, the biology and physiology of these nonaggregated cells is examined. A technique to separate aggregated cells from nonaggregated cells was developed; then differentiating cells at stages throughout the course of development were isolated. In this report we (i) describe peripheral rods, those cells which remain outside aggregates after aggregation has ceased in the rest of the population; (ii) document the occurrence of peripheral rods in several wild-type strains; and (iii) characterize the expression of developmentally regulated genes in both aggregated and nonaggregated cells. These studies have shown that myxobacterial hemagglutinin, protein S (Tps), protein S1 (Ops), protein C, and several phosphatase activities are expressed in cell-type-specific patterns. These data demonstrate that peripheral rods constitute a cell type distinct from either vegetatively growing cells or spores. The description of a second, late developmental cell type (in addition to spores) opens an entirely new line of investigation in M. xanthus, i.e., the regulation of the differentiation of vegetatively growing cells into two cell types that differ significantly in biology, shape, and localization within the population.

Transcription of the myxobacterial hemagglutinin gene is mediated by a sigma 54-like promoter and a cis-acting upstream regulatory region of DNA

Myxobacterial hemagglutinin (MBHA) is a major developmentally induced protein that accumulates during the period of cellular aggregation of the fruiting bacterium Myxococcus xanthus. In this study, DNA sequences mediating the transcriptional regulation of mbhA have been identified. Examination of nucleotide sequences upstream of the start site for mbhA transcription has indicated a region of DNA that bears strong homology to the consensus sequence for promoters recognized by the sigma 54 holoenzyme form of RNA polymerase of Escherichia coli and other eubacteria. Deletion of this sequence completely abolished mbhA transcription. Additionally, a cis-acting DNA element, affecting the efficiency of mbhA transcription, has been mapped within a region of DNA 89 to 276 nucleotides upstream of the sigma 54-like sequence. Transposon insertions, mapping within the cis element, drastically reduced mbhA transcriptional activity. These observations suggest that transcription of mbhA requires a productive interaction between a form of RNA polymerase that recognizes a sigma 54-like sequence and a transcriptional activator that binds to DNA sequences upstream of the mbhA promoter.

Myxococcus xanthus protein C is a major spore surface protein

Fruiting body formation in Myxococcus xanthus involves the aggregation of cells to form mounds and the differentiation of rod-shaped cells into spherical myxospores. The surface of the myxospore is composed of several sodium dodecyl sulfate (SDS)-soluble proteins, the best characterized of which is protein S (Mr, 19,000). We have identified a new major spore surface protein called protein C (Mr, 30,000). Protein C is not present in extracts of vegetative cells but appears in extracts of developing cells by 6 h. Protein C, like protein S, is produced during starvation in liquid medium but is not made during glycerol-induced sporulation. Its synthesis is blocked in certain developmental mutants but not others. When examined by SDS-polyacrylamide gel electrophoresis, two forms of protein C are observed. Protein C is quantitatively released from spores by treatment with 0.1 N NaOH or by boiling in 1% SDS. It is slowly washed from the spore surface in water but is stabilized by the presence of magnesium. Protein C binds to the surface of spores depleted of protein C and protein S. Protein C is a useful new marker for development in M. xanthus because it is developmentally regulated, spore associated, abundant, and easily purified.

Purification and properties of Myxococcus xanthus cell surface antigen 1604

A cell surface antigen complex from Zwittergent-solubilized Myxococcus xanthus has been purified by immunoaffinity chromatography with monoclonal antibody (MAb) 1604 and by subsequent gel filtration. We propose that the cell surface antigen (CSA) 1604 complex participates in intercellular interactions. The apparent total molecular mass of the CSA 1604 complex is 200 kilodaltons (kDa), as determined by gel filtration and by electrophoresis and Western immunoblot probing with MAb 1604. The antigen epitope recognized by MAb 1604 is on a 51-kDa polypeptide. The CSA complex also contains 14% neutral carbohydrate and a 23-kDa polypeptide that lacks the 1604 epitope. The carbohydrate is most likely part of a lipopolysaccharide (LPS) associated with the CSA, because an MAb recognizing an O antigen epitope from the LPS of M. xanthus also reacted with CSA 1604 on Western immunoblots. Thus, the 200-kDa CSA complex consists of 97 +/- 6 kDa of protein and many associated LPS molecules. The LPS evidently produces the multiplicity of bands observed on Western immunoblots between 100 and 200 kDa. The association with LPS may contribute to the negative charge of the CSA 1604 complex, which has a pI of 4.3. The CSA was clustered on the surface of intact M. xanthus cells after labeling with MAb 1604 and immunogold. Furthermore, fractionation studies indicated that cells grown on a plastic surface had 50% of their total CSA 1604 in the cytosol, 39% in the membrane fraction, and 8% in the periplasm. Saturable binding studies with 125I-MAb 1604 indicated that there were 2,400 CSA 1604 sites per cell. The Kd for MAb 1604 binding to the cell was 9 nM.

The role of the cell surface in social and adventurous behaviour of myxobacteria

The myxobacteria are an unusually social group of prokaryotic organisms that form fruiting bodies containing dormant myxospores in response to nutritional stress. Social behaviour is controlled by a multigene system known as 'S' and by a series of intercellular signals that are released during development. The genes controlling these communication systems have been identified by mutational analysis and current research is directed toward examining the functions of these genes. S- mutants are generally nondevelopmental and noncohesive. They lack pili, a Congo red receptor, and 50-nm-wide fibrils which extend outward from the cell surface. Changes in the architecture of the cell surface have been studied by means of surface labelling and with monoclonal antibodies directed against cell-surface antigens. The cell surface undergoes dramatic changes during the course of development. Most vegetative antigens decrease in concentration or disappear completely while new development-specific antigens appear.

Acceleration of starvation- and glycerol-induced myxospore formation by prior heat shock in Myxococcus xanthus

The effect of heat shock on Myxococcus xanthus was investigated during both glycerol- and starvation-induced development. Cells heat shocked at 40 degrees C for 1 h prior to a development-inducing signal displayed an accelerated rate of myxospore formation at 30 degrees C. Additionally, M. xanthus cells heat shocked prior to glycerol induction formed a greater total number of myxospores when sporulation was complete than did control cells maintained at 30 degrees C. However, in starvation-induced fruiting cells the total number of myxospores in control and heat-shocked populations was about equal when fruiting body and myxospore formation was complete. When extended heat shock (3 h) was applied to cells prior to development, no acceleration of myxospore formation was observed. Heat shock elicited the premature expression of many developmentally regulated proteins. Cell fractionation and analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography revealed the subcellular location and molecular weights of the 18 glycerol-induced and 9 starvation-induced developmental proteins. Comparison with previously identified M. xanthus heat shock proteins showed that nine of the developmental proteins found in glycerol-induced cells and three of the developmental proteins found in starvation-induced cells were heat shock proteins. Furthermore, heat shock increased the activity of alkaline phosphatase, a developmentally regulated enzyme, in vegetative cells, glycerol-induced cells, and starvation-induced cells.

Cloning of the gene for myxobacterial hemagglutinin and isolation and analysis of structural gene mutations

Myxobacterial hemagglutinin (MBHA) is a major developmentally induced protein that accumulates during the period of cellular aggregation in the bacterium Myxococcus xanthus. It has been shown that this lectin is targeted to the cell surface and periplasmic space of developmental cells, suggesting that it may play a role in cell-cell recognition or agglutination. We have cloned the structural gene for MBHA by using synthetic deoxyoligonucleotides containing sequences deduced from the amino acid sequence of MBHA and have used the cloned gene to construct strains of M. xanthus that cannot synthesize MBHA. We found that although the MBHA-deficient strains are delayed in their developmental time course, they are otherwise able to aggregate and sporulate normally. Our results suggest that MBHA may function to increase the efficiency of fruiting-body formation but is not a critical component of cellular aggregation.

Control of morphogenesis in myxobacteria

The myxobacteria are Gram-negative soil bacteria that live in large communities known as swarms. The most remarkable characteristic of myxobacteria is their ability to form fruiting bodies that have a species-specific shape and color. Fruiting body formation requires the concerted effort of hundreds of thousands of cells. Development is initiated only when two conditions are satisfied. The cells must be nutritionally deprived (environmental signal) and there must be many other cells in the vicinity (intercellular signal). The development of one species, Myxococcus xanthus, has been studied in the most detail. M. xanthus uses amino acids as its primary carbon, nitrogen, and energy source. Starvation for a single amino acid, or for inorganic phosphate, serves as the environmental signal. A variety of intercellular signals appear to control the initiation of development and the timing of subsequent developmental events.

Heat shock proteins of vegetative and fruiting Myxococcus xanthus cells

The heat shock response of Myxococcus xanthus was investigated and characterized. When shifted from 28 to 40 degrees C, log-phase cells rapidly ceased growth, exhibited a 50% reduction in CFU, and initiated the synthesis of heat shock proteins (HTPs). Heat-shocked log-phase M. xanthus cells labeled with [35S]methionine were found to produce 18 major HTPs. The HTPs, analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography, were characterized with regard to molecular mass, subcellular location (periplasm, membrane, or cytoplasm), and temperature required for expression. Most HTPs were expressed at 36 degrees C, the optimum growth temperature of M. xanthus. Cells preincubated at 36 degrees C for 1 h before being shifted to 40 degrees C demonstrated increased thermotolerance compared with cells shifted directly from 28 to 40 degrees C. The HTPs produced by heat-shocked starvation-induced fruiting cells and glycerol-induced sporulating cells were also analyzed and characterized. Thirteen HTPs were detected in fruiting cells shifted from 28 to 40 degrees C. Six of these HTPs were not seen in vegetative M. xanthus cells. Log-phase cells induced to sporulate by the addition of glycerol produced 17 HTPs after being shifted to 40 degrees C. These HTPs were found to be a mixture of HTPs detected in heat-shocked log-phase cells and heat-shocked fruiting cells.

Cell interactions in myxobacterial growth and development

During their complex life cycle, myxobacteria manifest a number of cell interactions. These include contact-mediated interactions as well as those mediated by soluble extracellular signals. Some of these interactions are well-defined; in addition, the tools for molecular and genetic analysis of these interactions in Myxococcus xanthus are now available.

Differential expression of protein S genes during Myxococcus xanthus development

Protein S, the most abundant protein synthesized during development of the fruiting bacterium Myxococcus xanthus, is coded by two highly homologous genes called protein S gene 1 (ops) and protein S gene 2 (tps). The expression of these genes was studied with fusions of the protein S genes to the lacZ gene of Escherichia coli. The gene fusions were constructed so that expression of beta-galactosidase activity was dependent on protein S gene regulatory sequences. Both the gene 1-lacZ fusion and the gene 2-lacZ fusion were expressed exclusively during fruiting body formation (development) in M. xanthus. However, distinct patterns of induction of fusion protein activity were observed for the two genes. Gene 2 fusion activity was detected early during development on an agar surface and could also be observed during nutritional downshift in dispersed liquid culture. Gene 1 fusion activity was not detected until much later in development and was not observed after downshift in liquid culture. The time of induction of gene 1 fusion activity was correlated with the onset of sporulation, and most of the activity was spore associated. This gene fusion was expressed during glycerol-induced sporulation when gene 2 fusion activity could not be detected. The protein S genes appear to be members of distinct regulatory classes of developmental genes in M. xanthus.

Gene expression during development of Myxococcus xanthus. Analysis of the genes for protein S

Protein S is an abundant spore coat protein produced during fruiting body formation (development) of the bacterium Myxococcus xanthus. We have cloned the DNA which codes for protein S and have found that this DNA hybridizes to three protein S RNA species from developmental cells but does not hybridize to RNA from vegetative cells. The half-life of protein S RNA was found to be unusually long, about 38 minutes, which, at least in part, accounts for the high level of protein S synthesis observed during development. Hybridization of restriction fragments from cloned M. xanthus DNA to the developmental RNAs enabled us to show that M. xanthus has two directly repeated genes for protein S (gene 1 and gene 2) which are separated by about 10(3) base-pairs on the bacterial chromosome. To study the expression of the protein S genes in M. xanthus, eight M. xanthus strains were isolated with Tn5 insertions at various positions in the DNA which codes for protein S. The strains which contained insertions in gene 1 or between gene 1 and gene 2 synthesized all three protein S RNA species and exhibited normal levels of protein S on spores. In contrast, M. xanthus strains exhibited normal levels of protein S on spores. In contrast, M. xanthus strains with insertions in gene 2 had no detectable protein S on spores and lacked protein S RNA. Thus, gene 2 is responsible for most if not all of the production of protein S during M. xanthus development. M. xanthus strains containing insertions in gene 1, gene 2 or both genes, were found to aggregate and sporulate normally even though strains bearing insertions in gene 2 contained no detectable protein S. We examined the expression of gene 1 in more detail by constructing a fusion between the lacZ gene of Escherichia coli and the N-terminal portion of protein S gene 1 of M. xanthus. The expression of beta-galactosidase activity in an M. xanthus strain containing the gene fusion was shown to be under developmental control. This result suggests that gene 1 is also expressed during development although apparently at a much lower level than gene 2.

Iodination of Myxococcus xanthus during development

Intact cells of Myxococcus xanthus were iodinated with [125I]lactoperoxidase to permit examination of the surface components accessible to labeling during cell development. Vegetative cells, starved on a defined solid medium, aggregated, formed fruiting bodies, and produced myxospores. Cells collected at different stages were iodinated, and their proteins were analyzed by one- and two-dimensional electrophoresis and autoradiography. One-dimensional electrophoresis revealed six iodinated bands in vegetative cell extracts. During development, 10 radioactive bands were detected, 4 of which migrated to the same positions as those of vegetative cells. Only six bands were detected in purified, labeled myxospores. Of these, one band possessed mobility similar to that of labeled vegetative cell proteins, whereas the other bands possessed mobility similar to that detected in developing cells. Analysis of two-dimensional gels indicated that at least 14 proteins were iodinated in vegetative cells, one of which was intensely labeled (protein b). Another of the proteins (protein a) was labeled throughout development. During development, about 30 proteins were iodinated and the prominently labeled ones were designated c, d, e, f, and g. The latter two (proteins f and g) were not detected in purified, iodinated myxospores. The data indicated a pronounced change in surface structure during development; some of the change may be involved in cellular interaction during aggregation.

Transport and localization of protein S, a spore coat protein, during fruiting body formation by Myxococcus xanthus

Protein S, the most abundant soluble protein synthesized by Myxococcus xanthus FB during early fruiting body formation, accumulates in the soluble fraction of developing cells, reaching a peak at about 24 h; at late stages of fruiting body formation, protein S is found on the surface of spores (M. Inouye et al. Proc. Natl. Acad. Sci. U.S.A. 76:209-213, 1979). In this study, the transport and localization of protein S were investigated. Cells were fractionated to give osmotic shock, membrane, cytoplasmic, and spore fractions. The various fractions were then analyzed for protein S. Protein S was first detected in the cytoplasmic fraction at about 3 to 6 h of development. However, transport of protein S through the cytoplasmic membrane was not observed until 15 to 18 h of development. Thus, protein S is unusual among translocated proteins in that it accumulates as a soluble cytoplasmic protein before translocation. Biosynthesis of protein S ceased after 48 h; by 72 h, protein S was only found on the surface of spores. Pulse-chase experiments were performed to determine the transport kinetics of protein S. The results showed that in 24-h developing cells, the transport of protein S across the cytoplasmic membrane was rapid, occurring in less than 2 min. However, transport across the outer membrane was slow, requiring 10 to 15 min. Pulses of 15 s with [35S]methionine failed to reveal any short-lived precursor form in immunoprecipitated material separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Isoelectric focusing also failed to detect any precursor form of protein S. Thus, protein S appears to be translocated in the absence of a cleaved signal peptide.

RNA polymerase of Myxococcus xanthus: purification and selective transcription in vitro with bacteriophage templates

DNA-dependent RNA polymerase from vegetative cells of the gram-negative, fruiting bacterium Myxococcus xanthus was purified more than 300-fold by a modified Burgess procedure (Lowe et al., Biochemistry 18:1344-1352, 1979), using Polymin P precipitation, 40 to 65% saturated ammonium sulfate fractional precipitation, double-stranded DNA cellulose chromatography, A5m gel filtration chromatography, and single-stranded DNA agarose chromatography. The last step separated the RNA polymerase into a core fraction and an enriched holoenzyme fraction. The core enzyme showed a subunit structure similar to that of the Escherichia coli polymerase, as follows: beta' and beta (145,000 and 140,000 daltons, respectively) and alpha (38,000 daltons). A comparison of the core enzyme and the holoenzyme implicated two polypeptides as possible sigma subunits. These polypeptides were closely related, as indicated by peptide analysis. M. xanthus RNA polymerase was capable of transcribing DNAs from E. coli phages T7, T4, and lambda, Bacillus subtilis phage phi 29, and M. xanthus phages Mx1, Mx4, and Mx8. Transcription of T7 and phi 29 DNAs was stimulated by KCl, whereas transcription of Mx1, Mx4, and Mx8 DNAs was inhibited by KCl. Magnesium ion dependence, rifampin and heparin sensitivities, and spermidine stimulation of M. xanthus RNA polymerase activity were similar to those found with E. coli RNA polymerase. The pH optimum of M. xanthus RNA polymerase activity was more basic than that of E. coli polymerase. M. xanthus RNA polymerase was capable of selective transcription in vitro when DNAs from phages T7 delta 111, phi 29, and Mx1 were used. The molecular weights of the resulting phage RNA transcripts made by M. xanthus RNA polymerase (as determined by agarose-acrylamide slab gel electrophoresis) were the same as the molecular weights of the transcripts synthesized by E. coli RNA polymerase. No discrete transcripts were detected as the in vitro RNA products of M. xanthus phage Mx4 and Mx8 DNA transcription. Southern transcript synthesized by M. xanthus RNA polymerase. Three transcripts (transcripts A, B, and C; molecular weights, 2.55 X 10(6), 1.95 X 10(6), and 1.56 X 10(6), respectively) were identified as in vitro RNA products of M. xanthus phage Mx1 DNA transcription when either E. coli or M. xanthus RNA polymerase was used. A Southern blot hybridization analysis indicated that the E. coli RNA polymerase and the M. xanthus RNA polymerase transcribe common SalI restriction fragments of Mx1 DNA.