A method for purifying an outer membrane protein of Haemophilus influenzae

Abstract: A method of purifying an immunogenic outer membrane protein of H. flu. The steps comprising, formation of an insoluble fraction comprising the outer membrane protein associated with the peptidoglycan from the H. flu; digesting contaminated RNA from the insoluble fraction; separating the outer membrane protein from the insoluble fraction into the supernatant; and concentrating the solubilized outer membrane protein.

Description: BACKGROUND OF THE INVENTION Haemophilus influenzae type b has long been recognized as a frequent pathogen, particularly in infants and children, but only recently has nontypable H. influenzae been recognized as an important pathogen. It is now well established that nontypable H. influenzae causes pneumonia, bacteremia, meningitis, postpartum sepsis, and acute febrile tracheobronchitis in adults. In addition, nontypable H. influenzae causes neonatal sepsis and is a frequent etiologic agent in acute otitis media in infants and children. Therefore, the importance of discovering a method to assay a clinical sample such as sputum, cerebral spinal fluid, blood and others for the presence of H. influenzae is clear. The observation that nontypable H. influenzae causes serious infections in adults and children has stimulated interest in study of the pathogenesis and potential virulence factors associated with this bacterium. The ribitol capsule of H. influenzae type b is a virulence factor for the organism, and antibody to capsule protects the host by means of bactericidal and/or opsonizing actions. These observations have generated much investigation on the role of the capsular polysaccharide in infection with H. influenzae type b and protection from these infections. However, nontypable H. influenzae lacks a polysaccharide capsule, and, similar to the outer membranes of other gram-negative bacteria, the outer membrane of H. influenzae is composed of outer membrane proteins (OMPs) and lipopolysaccharide (LPS). Therefore, studies of the relationship between virulence of nontypable H. influenzae and surface antigens focus on OMPs and LPS. Analysis of OMPs of nontypable H. influenzae has shown that there are marked differences in OMP composition among strains. See e.g. Murphy et at, "A Subtyping System For Nontypable Haemophilus influenzae Based on Outer-membrane Proteins," J. Infect. Dis, 1983, 147:838-46; Barenkamp et al, "Outer Membrane Protein and Biotype Analysis of Pathogenic Nontypable Haemophilus influenzae ," Infect. Immun, 1982, 36:535-40; Lorb et al, "Outer Membrane Protein Composition in Disease Isolates of Haemophilus influenzae , Pathogenic and Epidemiological Implications," Infect. Immun, 1980, 30:709-17. A subtyping system for nontypable H. influenzae based on the major OMPs has previously been developed. A surface exposed antigen (immunogen) which is conserved in all strains is an important tool in developing a method of identifying H. influenzae in clinical specimens as well as a vaccine against H. influenzae . A relatively simple method for purifying the conserved surface exposed antigen would be desirable. Methods that have been used included the step of initially isolating the outer membrane and the resultant products contained contaminating RNA, other cellular components and detergents. Illustrative for such more complicated and/or less effective processes are the methods as described in WO 88/04932 and Infection and Immunity 54/3 (1986), 744-9. It is therefore an object of this invention to provide a method for purifying the conserved surface exposed antigen, which is relatively simple and produces an increased yield of the desired antigen. It is a further object of this invention to provide a purification method which will produce a product free of contaminating RNA and undesirable cellular components. BRIEF DESCRIPTION OF THE INVENTION In accordance with the present invention there is provided a method for purifying an immunogenic outer membrane protein of H. influenzae (H. flu) consisting essentially of steps (a) to (f) of claim 1. DETAILED DESCRIPTION OF THE INVENTION A method for purifying the outer membrane protein of Haemophilus influenzae is disclosed in this invention. The method disclosed herein is relatively simpler than previous methods. The method utilizes the whole bacterium as a starting material for incubation in detergent containing buffers, therefore eliminating the initial step of isolating the outer membrane, as was necessary in previous methods. By whole bacterium is meant that the bacterium is used in an unprocessed state. H. flu, in a suspending medium, is used to directly obtain a first fraction comprising the outer membrane protein associated with peptidoglycan. The suspending medium is a liquid in which the fraction is insoluble and may be a detergent buffer. By detergent buffer is meant a buffer solution comprising a detergent wherein the outer membrane protein and the peptidoglycan are insoluble. Suitable detergents include sodium dodecyl sulfate (SDS). An example of a suitable detergent buffer is Buffer B. Buffer B comprises 1% SDS, 0.1% Beta-mercaptoethanol, 0.01M tris, 0.5M NaCl, pH 8.0. The first fraction comprising the outer membrane protein (p6) associated with peptidoglycan is obtained by successively heat treating and centrifuging the suspension. The suspension may be sonicated briefly to help suspend the cells. Heat treatment may be by any suitable means known to those skilled in the art. An example of a suitable means for heat treatment is incubation at between about 20°C to about 37°C for between about 20 to 40 minutes. Centrifugation is at about 20,000g to about 40,000g for about 30-60 minutes at ambient temperature. Ambient temperature as used herein means between about 20°C to about 27°C. By successive heat treatment and centrifugation is meant that the H. flu, in the suspending medium, is heat treated then centrifuged then resuspended in the suspending medium and heat treated and centrifuged until the first fraction comprising the p6 associated with peptidoglycan is formed. Contaminating RNA is then digested from the first fraction by use of a digesting material in a first liquid in which the peptidoglycan associated with the outer membrane protein remains insoluble and the digested contaminating RNA is soluble, such that a second fraction is formed. The second fraction is insoluble in the first liquid and comprises the outer membrane protein associated with peptidoglycan. By contaminating RNA is meant RNA which is present in the second fraction along with p6 and peptidoglycan. A digesting material allows for the digestion of contaminating RNA while the p6 remains in an insoluble form by virtue of its association with peptidoglycan. An example of a digesting material is ribonuclease A. The first liquid may be a detergent buffer as discussed supra. By soluble is meant selectively suspendable or removable with respect to the second fraction. Digesting material is added to the detergent buffer and the mixture is sequentially heat treated and centrifuged. Heat treatment and centrifuging are as described supra. By sequential heat treatment and centrifuging is meant that the first fraction is suspended in the detergent buffer comprising the digesting material and heat treated and centrifuged until contaminating RNA is digested and the second fraction is formed. The outer membrane protein (p6) is separated from the second fraction by suspending in a second liquid in which said outer membrane protein is soluble and the peptidoglycan is insoluble and heat treating to release the outer membrane protein from the peptidoglycan to obtain a third liquid comprising the solubilized outer membrane protein. An example of a liquid in which said outer membrane protein is soluble and the peptidoglycan is insoluble is a detergent free buffer. By detergent free buffer is meant a buffer solution not having a detergent added. Examples of suitable detergent free buffer solutions are tris buffer, PBS and sodium tetraborate buffer. A preferred detergent free buffer is sodium tetraborate buffer. The second fraction is suspended in the detergent free buffer and heat treated at between about 50-75°C for about 30-60 minutes. The suspension is then centrifuged at about 80,000g to about 120,000g for a sufficient time at a sufficient temperature until a supernatant (third liquid) comprising the outer membrane protein is obtained. The supernatant is then recovered which comprises a soluble preparation of p6 which is free of undesirable cellular components. Undesirable cellular components include lipooligosaccharides, proteins other than p6, peptidoglycan, DNA and RNA. The supernatant is then concentrated by means known to those skilled in the art and includes the method of pressure filtration. The following example describes the manner and process of making and using the invention and set forth the best mode contemplated by the inventor of carrying out the invention, but is not to be construed as limiting. Bacteria were grown in broth and 25 grams of bacteria were suspended in Buffer B, sonicated briefly to help suspend the cells and incubated at 37°C for 30 minutes. After incubation the suspension was centrifuged at 20,000g for 30 minutes at 25°C. The supernatant was discarded and the insoluble fraction was resuspended in Buffer B, incubated, and centrifuged as before. This cycle of incubations and centrifugations was repeated a total of 5 times. For the last two incubations, ribonuclease A (10 micrograms/ml) is added to Buffer B. Including the ribonuclease at this step allows for digestion of contaminating RNA while the p6 remains in an insoluble form by virtue of its association with peptidoglycan. In this way, the ribonuclease and the RNA degradation products remain soluble while p6 and peptidoglycan remain insoluble. The p6/peptidoglycan insoluble fraction was suspended in 0.1M Sodium tetraborate buffer (pH 9.5) and incubated for 30 minutes at 65° C. The mixture was then centrifuged at 100,000 g for one hour at 35° C. This step releases p6 from peptidoglycan so that solubilized, p6 remains in the supernatant. This supernatant was then concentrated by pressure filtration approximately ten fold. The volume was brought back up to its original volume and reconcentrated. This concentrating and washing procedure was done five times using the borate buffer. The resulting p6 preparations have been characterized as follows: SDS-PAGE yields a single protein band at a molecular weight of approximately 16,000 daltons. The preparation is free of detectable lipooligosaccharide using a monoclonal antibody. An absorbance spectrum of the soluble p6 revealed a peak at a wavelength of 275 nM. Agarose-gel electrophoresis revealed that the preparation is free of DNA and RNA. Therefore, the final preparation contains purified, solubilized p6 protein from Haemophilus influenzae. Amino acid analysis of this material shows that the amino acid content is consistent with that predicted from the DNA sequence disclosed herein. Other embodiments of the invention will be apparent to the skilled in the art from a consideration of this specification or practice of the invention disclosed herein. It should be understood that there may be other embodiments which fall within the spirit and scope of the invention as defined by the following claims.

Claims: A method for purifying an immunogenic outer membrane protein of Haemophilus influenzae consisting essentially of: a) suspending H. influenzae micro-organisms by incubating the organisms in a detergent buffer solution to form an insoluble fraction comprising the outer membrane protein and peptidoglycan component and a soluble fraction comprising the remainder of the cellular components; b) separating the insoluble fraction of step a) from the soluble fraction; c) suspending the insoluble fraction of step b) in detergent buffer containing digesting material that allows for digestion of contaminating RNA and allowing for RNA digestion; d) separating the insoluble fraction of step c) from the soluble fraction comprising the digesting material and digested RNA; e) solubilizing the insoluble fraction of step d) by heat-treating in a detergent-free buffer; and f) separating the soluble fraction containing the purified outer membrane protein from the insoluble fraction of step e) containing the peptidoglycan component. The method of claim 1, wherein the purified outer membrane protein is P6 having a molecular weight by SDS-PAGE under non-reducing conditions of from about 15,000 to about 17,000 daltons. The method of claim 1 or 2, wherein said detergent buffer solution of step a) comprises an anionic detergent. The method of claim 3, wherein said anionic detergent is sodium dodecyl sulfate. The method of one of claim 1 to 4, wherein said buffer solution is buffer B comprising 1 wt. % sodium dodecyl sulfate, 0.01 M Tris, 0.5 M NaCl, 0.1 % by volume beta-mercaptoethanol, pH 8.0. The method of one of claim 1 to 5, wherein step a) further comprises sonication of the micro-organisms in the detergent buffer solution to facilitate suspension of the cellular components. The method of one of claims 1 to 2, wherein said incubating of step a) is conducted by heat-treating the suspension at about 37°C for about 30 minutes. The method of one of claims 1 to 7, wherein the insoluble fraction is separated from the soluble fraction in step b) by centrifugation at about 100,000 xg for about 60 minutes, the insoluble fraction being in the form of a pellet. The method of claim 8, further including the steps of: resuspending the insoluble fraction in a buffer solution; and repeating the heat treating of step a) and b) until the insoluble fraction is substantially free of soluble cellular components. The method of one of claims 1 to 9, wherein said RNA digestion occurs by incubating the solution at about 37°C, for about 30 minutes. The method of one of claims 1 to 10, wherein the digesting material and digested RNA are separated out of the insoluble fraction in step d) by centrifugation. The method of one of claims 1 to 11, wherein said detergent-free buffer comprises 0.1 M sodium tetraborate, pH 9.5. The method of one of claims 1 to 12, wherein step f) further comprises: incubating the insoluble fraction at about 65°C for about 30 minutes; immediately thereafter centrifuging the insoluble fraction at about 100,000 xg for about 1 hour at about 37°C; and collecting the soluble fraction which contains the outer membrane protein. The method of claim 13, wherein the soluble fraction is treated with pressure filtration to concentrate the outer membrane protein. A method for purifying an outer membrane protein of Haemophilus influenzae consisting essentially of: a) suspending H. influenzae micro-organisms in a detergent buffer solution to form a suspension; b) heat-treating the suspension by incubating at about 37°C for about 30 minutes to form a soluble and insoluble fraction; c) separating the insoluble fraction from the soluble fraction by centrifuging the suspension of step b) at about 100,000 xg for about 60 minutes at ambient temperature, the insoluble fraction being in the form of a pellet comprising the outer membrane protein and peptidoglycan component and the soluble fraction comprising the remainder of the cellular components; d) resuspending the pellet of step c) in a detergent buffer solution; e) repeating steps b) and c) until the insoluble fraction is substantially free of soluble cellular components; f) digesting RNA present in the insoluble fraction by adding ribonuclease A and incubating at about 37°C for about 30 minutes; g) repeating step c) to remove the ribonuclease A which will be contained in the soluble fraction; h) solubilizing the insoluble fraction of step g) in a detergent-free buffer solution comprising 0.1 M sodium tetraborate, pH 9.5 by incubating at about 65°C for about 30 minutes; and i) separating the outer membrane protein from the peptidoglycan component by centrifuging the solution of h) at about 100,000 xg, for about 1 hour at about 37°C, wherein the supernatant comprises the outer membrane protein.

Inventors: APICELLA MICHAEL A, MURPHY TIMOTHY F, APICELLA, MICHAEL A., MURPHY, TIMOTHY F.
Applicants: UNIV NEW YORK, THE RESEARCH FOUNDATION OF STATE UNIVERSITY OF NEW YORK
Application year: 1990
Main classification: C07K1
IPC codes: C12P21, A61K39, C12R1