Amino acid replacements in the Serratia marcescens haemolysin ShlA define sites involved in activation and secretion

The haemolysin of Serratia marcescens (ShlA) is translocated through the cytoplasmic membrane by the signal peptide-dependent export apparatus. Translocation across the outer membrane (secretion) is mediated by the ShIB protein. Only the secreted form of ShlA is haemolytic. ShIB also converts in vitro inactive ShlA (ShlA*), synthesized in the absence of ShIB, into the haemolytic form (a process termed activation). To define regions in ShlA involved in both processes, ShlA derivatives were isolated and tested for secretion and activation. Analysis of C-terminally truncated proteins (ShlA) assigned the secretion signal to the amino-terminal 238 residues of ShlA. Trypsin cleavage of a secreted ShlA' derivative yielded a 15kDa N-terminal fragment, by which a haemolytically inactive ShlA* protein could be activated in vitro. It is suggested that the haemolysin activation site is located in this N-terminal fragment. Replacement of asparagine-69 and asparagine-109 by isoleucine yielded inactive haemolysin derivatives. Both asparagine residues are part of two short sequence motifs, reading Ala-Asn-Pro-Asn, which are critical to both activation and secretion. These point mutants as well as N-terminal deletion derivatives which were not activated by ShIB were activated by adding a non-haemolytic N-terminal fragment synthesized in an ShIB⁺ strain (complementation). Apparently the activated N-terminal fragment substituted for the missing activation of the ShlA derivatives and directed them into the erythrocyte membrane, where they formed pores. It is concluded that activation is only required for initiation of pore formation, and that in vivo activation and secretion are tightly coupled processes. Complementation may also indicate that haemolysin oligomers form the pores.     

Immobilization of chloroperoxidase from Serratia marcescens in protein semi-permeable membranes

A method for the immobilization of chloroperoxidase from the bacterial strain Serratia marcescens in semi-permeable membranes was developed based on the following proteins: bovine serum albumin, gelatin, ribonuclease, cytochrom C, and the protein of the covering layer of Bacillus sphaericus cells. Estimation of the activity and stability of immobilized preparations in a batch reactor was carried out.     

Immobilization of chloroperoxidase from Serratia marcescens in semi-permeable protein membranes

A method for the immobilization of chloroperoxidase from the bacterial strain Serratia marcescens in semi-permeable membranes was developed based on the following proteins: bovine serum albumin, gelatin, ribonuclease, cytochrom C, and the protein of the covering layer of Bacillus sphaericus cells. Estimation of the activity and stability of immobilized preparations in a batch reactor was carried out. Published in Russian in Prikladnaya Biokhimiya i Mikrobiologiya, 2006, Vol. 42, No. 2, pp. 152–155. This article was translated by the authors.     

Overproduction of Serratia marcescens metalloprotease (SMP) from the recombinant Serratia marcescens strains

Summary To overproduce Serratia marcescens metalloprotease(SMP), various recombinant plasmids encoding SMP gene were constructed and the SMP productivities from the recombinant S. marcescens strains were examined. The recombinant S. marcescens strains indispensably required proteinaceous substrates such as casein for the extracellular production of SMP. We obtained maximum 9,100U/ml of SMP from the culture supernatant of S. marcescens ATCC27117 containing a regulatory plasmid pTSP2 encoding SMP gene fused with a strong trc99a promoter and its repressor gene lacI^q, which is about 23 times higher than that of wild type strain. SMP produced from the recombinant S. marcescens(pTSP2) was 88.3% of total extracellular proteins.     

Differentiation of Serratia marcescens 274 into swimmer and swarmer cells

We describe a new sensory response in the enteric bacterium Serratia marcescens. When grown in liquid media, the bacteria were short rods with one to two flagella and displayed classical swimming behavior. Upon transfer to a solid surface (0.7 to 0.8T% agar medium), the bacteria underwent a dramatic change of form. They ceased septation, elongated, and expressed numerous (10 to 100) flagella that covered the lateral sides of the cells. The bacteria now displayed a different form of locomotion--swarming--which allowed them to rapidly move over the top of the solid surface. The differentiation to either swimmer or swarmer cells could be reversed by growth on solid or liquid medium, respectively. To identify conditions that influence this differentiation, the growth environment of S. marcescens was manipulated extensively. The swarming response was monitored by visual and microscopic observation of cell movement on solid surfaces, by immunofluorescent labeling followed by microscopic observation for the presence of elongated, profusely flagellated cells, as well as by estimation of induction of flagellin protein, using Western immunoblot analysis. Conditions that imposed a physical constraint on bacterial movement, such as solid or viscous media, were the most efficient at inducing the swarming response. No chemical constituent of the medium that might contribute to the response could be identified, although the existence of such a component cannot be ruled out. Both swimmer and swarmer cells had flagellin proteins of identical molecular weight, which produced similar proteolysis patterns upon digestion with trypsin.     

Incorporation of the human erythrocyte sialoglycoprotein into recombined membranes containing cholesterol

Summary Glycophorin, the major sialoglycoprotein from the human erythrocyte membrane, has been isolated and recombined with phosphatidylcholine and cholesterol. Sucrose density gradient analysis of the recombinants shows that it is possible not only to recombine this protein with phospholipid, but also with phospholipid-cholesterol mixtures. Surprisingly, by the same analysis, it was possible to make a recombinant with cholesterol and glycophorin, only, in the absence of added phospholipid. The accessibility of the protein to trypsin was tested in each of these recombinants. In all the recombinants which contained either phospholipid, or phospholipid and cholesterol, the protein was protected from extensive hydrolysis. This is consistent with closed vesicles and incorporation of the protein into the recombinant membrane. Extensive hydrolysis of the protein occurred in the cholesterol-glycophorin recombinant indicating some differences in structure. Freeze-fracture electron microscopy of the phospholipid and the phospholipid-cholesterol recombinants showed mostly unilamellar vesicles, 1000 to 5000 Å in diameter. Intramembranous particles were observed on both fracture faces, and the fracture planes were those expected for phospholipid bilayers. The glycophorin-cholesterol recombinants also showed fracture planes consistent with bilayers, and revealed intramembranous particles. Pieces of membrane-like structures as well as apparent vesicular structures were observed. Finally in the recombinants of glycophorin with phospholipid and cholesterol, cholesterol is shown to reduce the population of the motionally restricted phospholipid headgroup environment, in proportion to the mole percent cholesterol content.     

Cloning of the Serratia marcescens recA gene and construction of a Serratia marcescens recA mutant

A recombinant plasmid, pSM2513, containing an 8.5 kb DNA insert was isolated from a genomic library of Serratia marcescens by using interspecific complementation. This plasmid conferred resistance to methyl methanesulphonate and UV irradiation upon recA mutants of Escherichia coli and enhanced recombination proficiency, as measured by Hfr-mediated conjugation, in recA mutants of E. coli. Furthermore, when recA mutants of E. coli harbouring pSM2513 were subjected to UV irradiation, filamentation of the cells was observed. This did not occur upon UV irradiation of the same mutants harbouring the cloning vector alone. These results imply that the S. marcescens recA gene on pSM2513 is functionally similar to the E. coli recA gene in several respects. Restriction enzyme analysis and subcloning studies revealed that the S. marcescens recA gene was located on a 2.7 kb Bg/II-KpnI fragment of pSM2513, and its gene product of approximately 39 kDa resembled the E. coli RecA protein in molecular mass. Using transformation-mediated marker rescue, a recA mutant of S. marcescens was successfully constructed; its proficiency both in homologous recombination and in DNA repair was abolished compared with its parent.     

Pili mediated agglutination of Serratia marcescens in human urine

Of 51 strains of Serratia marcescens isolated from patients with urinary or respiratory tract infections, 35 agglutinated in human urine. The agglutinating strains possessed numerous pili which were morphologically distinct from common pili or type I pili. The diameter of the pili was 3 nm and the average length was 0.3 micrometer. Electron microscopic examination showed that 80% or more of the cells of the agglutinating strains and 0 to 8% of the cells of the nonagglutinating strains were piliated. When an agglutinating strain was heated at 55 C for 10 min, it lost its agglutinating capacity and concomitantly its pili. These results suggest that the agglutination might occur because of interactions between the pili and some factors in human urine. The urinary slime appears to contain these agglutinating factors.     

Hemolytic activity of Serratia marcescens

A cell-bound hemolytic activity was found in several strains of Serratia marcescens. One Serratia cell per ten erythrocytes was sufficient to cause complete lysis of human erythrocytes within 2 h in the liquid assay. The hemolytic activity resided in the membrane fraction and could be inactivated by incubating cells with proteases. The hemolytic activity was greatly enhanced in actively metabolizing Serratia cells and was partially controlled by the iron supply. Hemolysis was accompanied by degradation of erythrocyte membrane proteins (band 3 and 6, glycophorin) and was independent of the blood group. The exoprotease secreted by S. marcescens in large amounts was not involved in hemolysis. Comparison with various hemolytic strains of Escherichia coli showed that hemolysis of erythrocytes was more pronounced with S. marcescens than with E. coli. In contrast to hemolysis by E. coli, lysis of erythrocytes by S. marcescens was not enhanced by Ca²⁺ ions.Dedicated to Professor Dr. Gerhart Drews on the occasion of his 60th birthday     

Incorporation of Na,K-ATPase into human erythrocyte membranes using liposomes

A procedure for incorporation of isolated cattle brain Na,K-ATPase into erythrocyte membranes by proteoliposomes has been elaborated. The Na,K-ATPase activity of proteoliposome-treated human erythrocytes containing incorporated Na,K-ATPase does not exceed that of control erythrocytes. In the erythrocyte membrane the incorporated enzyme exists in a functionally active state and retains the vector properties of the Na+-pump. Exogenous ATP stimulates 22Na influx and 86Rb efflux in and from the erythrocytes.     

Proteolytic activity associated with human erythrocyte membranes. Self-digestion of isolated human erythrocyte membranes

At least two kinds of enzymes are active in the proteolytic self-digestion of erythrocyte membranes. The specific activities of these enzymes do not decrease with repeated washings of purified stroma. The effects of a variety of inhibitors on the membrane preparation's capacity to digest ¹²⁵I-labelled casein, covalently linked to latex beads, have been examined.Pepstatin-inhibitable enzyme, active at low pH, digests the membrane extensively to small polypeptide fragments. Spectrin, located at the internal part of the membrane, is readily degraded. Diisopropylfluorophosphate-inhibitable enzyme, active at pH 8–9, has only limited digestive capacity. Some of the membrane components, such as the small molecular weight glycoproteins, are resistant to digestion. The restricted capacity of digestion is due to the membrane molecular arrangement; increased disaggregation removes the restriction and increases the activity. Spectrin is not digested unless the membrane topography is disrupted by NP-40 neutral detergent. These observations suggest that the enzymes active at basic pH are located external to the cell. Intact cells do possess a limited capacity to degrade ¹²⁵I-labelled casein when their surfaces are brought into contact with substrate-coated beads.     

Identification of the Serratia marcescens hemolysin determinant by cloning into Escherichia coli.

A cosmid bank of Serratia marcescens was established from which DNA fragments were cloned into the plasmid pBR322, which conferred the chromosomally encoded hemolytic activity to Escherichia coli K-12. By transposon mutagenesis with Tn1000 and Tn5 IS50L::phoA (TnphoA), the coding region was assigned to a DNA fragment, designated hly, comprising approximately 7 kilobases. Two proteins with molecular weights of 61,000 (61K protein) and 160,000 (160K protein) were expressed by the pBR322 derivatives and by a plasmid which contained the hly genes under the control of a phage T7 promoter and the T7 RNA polymerase. When strongly overexpressed the 160K protein was released by E. coli cells into the extracellular medium concomitant with hemolytic activity. The genes encoding the 61K and the 160K proteins were transcribed in the same direction. Mutants expressing a 160K protein truncated at the carboxy-terminal end were partially hemolytic. Hemolysis was progressively inhibited by saccharides with increasing molecular weights from maltotriose (Mr 504) to maltoheptaose (Mr 1,152) and was totally abolished by dextran 4 (Mr 4,000). This result and the observed influx of [14C]sucrose into erythrocytes in the presence of hemolytic E. coli transformants under osmotically protective conditions suggest the formation of defined transmembrane channels by the hemolysin.     

Immobilization of Chloroperoxidase from Serratia marcescens

A bacterial non-heme chloroperoxidase from Serratia marcescensW 250 was immobilized in calcium alginate gel. Methods for stabilization of the immobilized enzyme were developed, and some kinetic parameters of the immobilized preparations were determined. The enzyme encapsulated into the gel granules in the presence of potassium ferricyanide followed by treatment with glutaraldehyde demonstrated the highest stability under the reaction conditions.