High conversion in asymmetric hydrolysis during permeation through enzyme-multilayered porous hollow-fiber membranes

We describe a novel porous hollow-fiber support for immobilizing aminoacylase in multilayers. Epoxy-group-containing polymer chains were grafted onto a porous hollow-fiber membrane by radiation-induced graft polymerization of glycidyl methacrylate, and subsequently a diethylamino group as an anion-exchange group was introduced into the graft chain. Aminoacylase was adsorbed in multilayers by allowing the amioacylase buffer solution to permeate through the pores across the hollow fiber; the graft chains provided three-dimensional space for the enzymes because of their electrostatic repulsion. The adsorbed enzyme at a degree of multilayer binding of 15 was cross-linked with glutaraldehyde to prevent leakage. An acetyl-DL-methionine solution was allowed to permeate through the pores surrounded by the aminoacylase-immobilized graft chain. Production of L-methionine was observed at a 4.1 mol/h per L of the fiber for a space velocity of 200 h(-1), defined as the flow rate of the effluent penetrating the outside surface of the hollow fiber divided by the membrane volume including the lumen.     

Protein binding to amphoteric polymer brushes grafted onto a porous hollow-fiber membrane

Three kinds of ampholites, i.e., 3-aminopropionic acid (NH2C2H4COOH), (2-aminoethyl)phosphonic acid (NH2C2H4PO3H2), and 2-aminoethane-1-sulfonic acid (NH2C2H4SO3H), were introduced into an epoxy group-containing polymer brush grafted onto a porous hollow-fiber membrane with a porosity of 70% and pore size of 0.36 microm. The amphoteric group density of the hollow-fiber ranged from 0.50 to 0.72 mmol/g. Three kinds of proteins, i.e., lactoferrin (Lf), cytochrome c (Cyt c), and lysozyme (Ly), were captured by the amphoteric polymer brush during the permeation of the protein solution across the ampholite-immobilized porous hollow-fiber membrane. Multilayer binding of the protein to the amphoteric polymer brush, with a degree of multilayer binding of 3.3, 8.6, and 15 for Lf, Cyt c, and Ly, respectively, with the (2-aminoethyl)phosphonic acid-immobilized porous hollow-fiber membrane, was demonstrated with a negligible diffusional mass-transfer resistance of the protein to the ampholite immobilized. The 2-aminoethane-1-sulfonic acid-immobilized porous hollow-fiber membrane exhibited the lowest initial flux of the protein solution, 0.41 m/h at a transmembrane pressure of 0.1 MPa and 298 K, and the highest equilibrium binding capacity of the protein, e.g., 130 mg/g for lysozyme. Extension and shrinkage of the amphoteric polymer brushes were observed during the binding and elution of the proteins.     

Production of cycloisomaltooligosaccharides from dextran using enzyme immobilized in multilayers onto porous membranes

Anion-exchange porous hollow-fiber membranes with a thickness of about 1.2 mm and a pore size of about 0.30 microm were used as a supporting matrix to immobilize cycloisomaltooligosaccharide glucanotransferase (CITase). CITase was immobilized to the membrane via anion-exchange adsorption and by subsequent enzymatic cross-linking with transglutaminase, the amount of which ranged from 3 to 110 mg per gram of the membrane. The degree of enzyme multilayer binding was equivalent to 0.3-9.8. Dextran, as the substrate, was converted into seven- to nine-glucose-membered cycloisomaltooligosaccharides (CI-7, -8, and -9) at a maximum yield of 28% in weight at a space velocity of 10 per hour during the permeation of 2.0% (w/w) dextran solution across the CITase-immobilized porous hollow-fiber membrane. The yield of CIs increased with increasing degree of CITase multilayering.     

Capture of microbial cells on brush-type polymeric materials bearing different functional groups

A brush-type microbial-cell-capturing polymeric material was prepared by radiation-induced grafting of an epoxy-group-containing monomer, glycidyl-methacrylate (GMA), onto a polyethylene-based fiber. The epoxy ring (EO) of GMA was opened with different degrees of introduction of diethylamine (DEA). The residual epoxy group was hydrophilized by ethanolamine (EA). The prepared DEA membranes with coexisting EO or EA groups were tested for their ability to capture Staphylococcus aureus and Escherichia coli cells. The DEA membrane (2.7 mol/kg of product of DEA group density) with coexisting EO groups (DEA-EO membrane) exhibited good S. aureus-cell-capturing ability with a capturing rate constant of 1.82 x 10(-6) m/s, whereas the DEA membrane with coexisting EA groups (DEA-EA membrane) retarded capturing abilities for both S. aureus and E. coli cells. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 53: 523-528, 1997.     

Protein binding to polymer brush,based on ion-exchange,hydrophobic, and affinity interactions

The major limitations associated with conventional packed bed chromatography for protein separation and purification can be overcome by using adsorptive microporous membranes as chromatographic media. Microporous membranes have advantages as support matrices in comparison to conventional bead supports because they are not compressible and they eliminate diffusion limitations. As a result, higher throughput and shorter processing times are possible using these membrane systems. In this paper, we review the current state of development in the area of attaching functionalized polymer brushes onto a microporous membrane to form a novel chromatographic medium for protein separation and purification. The functionalized polymer brushes were appended onto the pore surface of a microporous hollow-fiber membrane uniformly across the membrane thickness by radiation-induced graft polymerization and subsequent chemical modifications. We review various applications of this adsorptive membrane chromatography by focusing on polymer brushes bearing ion-exchange, hydrophobic and affinity groups. Proteins were captured in multilayers by the ion-exchange group-containing polymer brushes due to the formation of a three-dimensional space for protein binding via the electrostatic repulsion of the polymer brushes. In contrast, proteins were captured in a monolayer at most by the polymer brushes containing hydrophobic or affinity ligands. By permeating a protein solution through the pores rimmed by the polymer brushes, an ideal capturing rate of the proteins with a negligible diffusional mass-transfer resistance was achieved by the functionalized polymer brushes, based on ion-exchange, hydrophobic, and affinity interactions.     

The role of polymer nanolayer architecture on the separation performance of anion-exchange membrane adsorbers: I. Protein separations

This contribution describes the preparation of strong anion-exchange membranes with higher protein binding capacities than the best commercial resins. Quaternary amine (Q-type) anion-exchange membranes were prepared by grafting polyelectrolyte nanolayers from the surfaces of macroporous membrane supports. A focus of this study was to better understand the role of polymer nanolayer architecture on protein binding. Membranes were prepared with different polymer chain graft densities using a newly developed surface-initiated polymerization protocol designed to provide uniform and variable chain spacing. Bovine serum albumin and immunoglobulin G were used to measure binding capacities of proteins with different size. Dynamic binding capacities of IgG were measured to evaluate the impact of polymer chain density on the accessibility of large size protein to binding sites within the polyelectrolyte nanolayer under flow conditions. The dynamic binding capacity of IgG increased nearly linearly with increasing polymer chain density, which suggests that the spacing between polymer chains is sufficient for IgG to access binding sites all along the grafted polymer chains. Furthermore, the high dynamic binding capacity of IgG (>130 mg/mL) was independent of linear flow velocity, which suggests that the mass transfer of IgG molecules to the binding sites occurs primarily via convection. Overall, this research provides clear evidence that the dynamic binding capacities of large biologics can be higher for well-designed macroporous membrane adsorbers than commercial membrane or resin ion-exchange products. Specifically, using controlled polymerization leads to anion-exchange membrane adsorbers with high binding capacities that are independent of flow rate, enabling high throughput. Results of this work should help to accelerate the broader implementation of membrane adsorbers in bioprocess purification steps.     

Highly multilayered urease decomposes highly concentrated urea

Urease was immobilized at a density of 1.2 g of urease per gram of a matrix via ion-exchange binding of urease to an anion-exchange polymer chain grafted onto a pore surface of a porous hollow-fiber membrane and subsequent cross-linking of urease with transglutaminase. Urea was hydrolyzed during the permeation of a urea solution, the concentration of which ranged from 2 to 8 M, through the pores of the resultant membrane with a thickness of approximately 1 mm. Quantitative hydrolysis of 4 M urea was achieved at a permeation rate lower than 1 mL/h, i.e., a residence time longer than 5.1 min, at ambient temperature. This performance is ascribed to convective transport of urea through the pores rimmed by the urease-immobilized polymer chains at a high density. Urease was denatured in the presence of urea at concentrations higher than 6 M while hydrolyzing urea.     

Production of tripeptide from gelatin using collagenase-immobilized porous hollow-fiber membrane

Tripeptide was produced during the permeation of a gelatin solution through the pore of a collagenase-immobilized porous hollow-fiber membrane. Gelatin was obtained via hydrolysis of fish collagen. First, an epoxy-group-containing monomer was graft-polymerized onto an electron-beam-irradiated porous hollow-fiber membrane. Second, the 2-hydroxyethylamino group was introduced into the epoxy group to bind collagenase on the basis of electrostatic interaction. Third, adsorbed collagenase was cross-linked with glutaraldehyde to prevent leakage of the enzyme. Gelatin solution (10-50 g/L) was forced to permeate across the collagenase-immobilized porous hollow-fiber membrane with a density of immobilized collagenase of 52 mg/g at various residence times of the gelatin solution ranging from 0.13 to 20 min. Fourteen percent in weight of 10 g/L gelatin solution was hydrolyzed into tripeptide at a residence time of 20 min.     

Ion-exchange macroporous hydrophilic gel monolith with grafted polymer brushes

The grafting of functional polymers to the pore surface of macroporous monolithic polyacrylamide cryogels was found to be an efficient and convenient method for the preparation of macroporous polyacrylamide gels, so-called cryogels (pAAm cryogels), with both controlled extent of functional group incorporated and with tailored surface chemistries. Anion-exchange polymer chains of poly(2-(dimethylamino)ethyl methacrylate) (pDMAEMA) and poly([2-(methacryloyloxy)ethyl]-trimethylammonium chloride) (pMETA), and cation-exchange polymer chains of polyacrylate have been grafted onto pAAm cryogels using potassium diperiodatocuprate as initiator. It was possible to achieve the ion-exchange capacity up to 0.2-0.5 mmol/ml. The graft polymerization did not alter the macroporous structure of the pAAm cryogel, however the flow rate of solutes through the cryogel matrix decreased with increase in the density of polymer grafted. The sorption of low-molecular-weight (metal ion, dye) and high-molecular-weight (protein) substances on the grafted monolithic pAAm column has been studied. The results indicate that a 'tentacle'-type binding of protein to grafted polymer depended on the architecture of the grafted polymer layer and took place after a certain degree of grafting has been reached. The binding of proteins by tentacle-like polymer chains allowed for increasing the binding capacity for proteins on the grafted pAAm cryogels up to 6-12 mg/ml.     

Changes in levels of pancreatic endoplasmic reticulum proteins that function in translocation and maturation of secretory proteins in response to cholecystokinin

Two pathways operate to target newly-synthesised proteins to the endoplasmic reticulum. In one, the signal recognition particle attaches to the signal sequences of nascent chains on ribosomes and slows or stops translation until contact is made with the docking protein at the membrane. The second operates via molecular chaperons. The pathways converge at the level of a 43 kDa signal binding protein integrated into the membrane, where translocation through a proteinaceous pore is initiated. In the lumen, proteins fold and disulphide formation is catalysed by the enzyme protein disulphide isomerase. The heavy chain binding protein may attach to unassembled or unfolded proteins and prevent their exit from the ER to the Golgi. Cholecystokinin (CCK) treatment increases the biosynthesis and secretion of pancreatic proteins, increases the levels of PDI and the 43 kDa binding protein, and reduces levels of BiP. These proteins may be possible targets for genetic manipulation to improve processing of heterologous proteins from cultured mammalian cells.     

The membrane-bound structure and topology of a human α-defensin indicate a dimer pore mechanism for membrane disruption

Defensins are cationic and disulfide-bonded host defense proteins of many animals that target microbial cell membranes. Elucidating the three-dimensional structure, dynamics, and topology of these proteins in phospholipid bilayers is important for understanding their mechanisms of action. Using solid-state nuclear magnetic resonance spectroscopy, we have now determined the conformation, dynamics, oligomeric state, and topology of a human α-defensin, HNP-1, in DMPC/DMPG bilayers. Two-dimensional correlation spectra show that membrane-bound HNP-1 exhibits a conformation similar to that of the water-soluble state, except for the turn connecting strands β2 and β3, whose side chains exhibit immobilization and conformational perturbation upon membrane binding. At high protein/lipid ratios, rapid (1)H spin diffusion from the lipid chains to the protein was observed, indicating that HNP-1 was well inserted into the hydrocarbon core of the bilayer. Arg Cζ-lipid (31)P distances indicate that only one of the four Arg residues forms tight hydrogen-bonded guanidinium-phosphate complexes. The protein is predominantly dimerized at high protein/lipid molar ratios, as shown by (19)F spin diffusion experiments. The presence of a small fraction of monomers and the shallower insertion at lower protein concentrations suggest that HNP-1 adopts concentration-dependent oligomerization and membrane-bound structure. These data strongly support a "dimer pore" topology of HNP-1 in which the polar top of the dimer lines an aqueous pore while the hydrophobic bottom faces the lipid chains. In this structure, R25 lies closest to the membrane surface among the four Arg residues. The pore does not have a high degree of lipid disorder, in contrast to the toroidal pores formed by protegrin-1, a two-stranded β-hairpin antimicrobial peptide. These results provide the first glimpse into the membrane-bound structure and mechanism of action of human α-defensins.     

Adsorption characteristics of an immobilized metal affinity membrane.

An immobilized metal affinity (IMA) hollow-fiber membrane was prepared by radiation-induced graft polymerization of glycidyl methacrylate (GMA) onto a porous polyethylene hollow fiber, followed by chemical conversion of the produced epoxide group into an iminodiacetate (IDA) group and its chelation with copper(II) ion. The IDA hollow fiber, whose degree of GMA grafting was 120%, was found to retain 0.42 mol of Cu ion/kg of dry weight of the resulting IMA hollow fiber. The pure water flux of the affinity membrane was 0.90 m/h at a filtration pressure of 1 x 10(5) Pa. The 0.1 g/L L-histidyl-L-leucine (His-Leu) solution permeated across the IMA hollow fiber, whose inner diameter and thickness were 0.78 and 0.365 mm, respectively, at a prescribed filtration pressure ranging from 0.2 x 10(5) to 1.0 x 10(5) Pa. The adsorption of His-Leu during permeation of the solution showed that the overall adsorption rate was independent of the filtration pressure, i.e., the residence time, because of the negligible diffusional resistance of His-Leu to the pseudobioaffinity ligand located on the pore surface of the membrane. No deterioration in the adsorption capacity was observed after five cycles of His-Leu adsorption, its elution, and reimmobilization of copper. The adsorption isotherm of bovine serum albumin (BSA) on the IMA hollow fiber was measured and compared with that for the conventional agarose-based bead containing the IDA-Cu ligand.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synthesis and application of chemically reactive proteins by the reversible modification of protein amino groups with exo-cis-3,6-endo-epoxy-4,5-cis-epoxyhexahydrophthalic anhydride.

The reversible reaction of exo-cis-3,6-endo-epoxy-4,5-cis-epoxyhexahydrophthalic anhydride (EEHPA) with free protein amino groups is described. The free protein amino groups of lysozyme can be completely blocked through the reaction of the anhydride EEHPA. The chemically less reactive epoxy groups in EEHPA-modified lysozyme remain intact during modification of the protein and can be used for many subsequent chemical reactions. Hydrolysis of the modified inactive lysozyme at pH 2.5 results in deblocking and almost complete recovery of the enzymic activity of the protein. The epoxy groups in EEHPA-modified proteins have a great many potential uses: disaggregation of supramolecular structures, conversion of hydrophobic membrane proteins or tryptic peptides into water-soluble coloured proteins or peptides, inhibition of tryptic cleavage at lysine residues, synthesis of chemically reactive proteins or enzymes for affinity chromatography or immobilized-enzyme technology, two-dimensional separation techniques for complex protein mixtures, detection of specific protein-binding sites for organic substrates or tumour diagnostics, synthesis of defined artificial glycoproteins for biophysical and cytochemical studies and chemical synthesis of radioactively labelled proteins.     

Removal of endotoxin from water by microfiltration through a microporous polyethylene hollow-fiber membrane

The microporous polyethylene hollow-fiber membrane has a unique microfibrile structure throughout its depth and has been found to possess the functions of filtration and adsorption of endotoxin in water. The membrane has a maximum pore diameter of approximately 0.04 micron, a diameter which is within the range of microfiltration. Approximately 10 and 20% of the endotoxin in tap water and subterranean water, respectively, was smaller than 0.025 micron. Endotoxin in these water sources was efficiently removed by the microporous polyethylene hollow-fiber membrane. Escherichia coli O113 culture broth contained 26.4% of endotoxin smaller than 0.025 micron which was also removed. Endotoxin was leaked into the filtrate only when endotoxin samples were successively passed through the membrane. These results indicate that endotoxin smaller than the pore size of the membrane was adsorbed and then leaked into the filtrate because of a reduction in binding sites. Dissociation of 3H-labeled endotoxin from the membrane was performed, resulting in the removal of endotoxin associated with the membrane by alcoholic alkali at 78% efficiency.     

Removal of endotoxin from water by microfiltration through a microporous polyethylene hollow-fiber membrane.

The microporous polyethylene hollow-fiber membrane has a unique microfibrile structure throughout its depth and has been found to possess the functions of filtration and adsorption of endotoxin in water. The membrane has a maximum pore diameter of approximately 0.04 micron, a diameter which is within the range of microfiltration. Approximately 10 and 20% of the endotoxin in tap water and subterranean water, respectively, was smaller than 0.025 micron. Endotoxin in these water sources was efficiently removed by the microporous polyethylene hollow-fiber membrane. Escherichia coli O113 culture broth contained 26.4% of endotoxin smaller than 0.025 micron which was also removed. Endotoxin was leaked into the filtrate only when endotoxin samples were successively passed through the membrane. These results indicate that endotoxin smaller than the pore size of the membrane was adsorbed and then leaked into the filtrate because of a reduction in binding sites. Dissociation of 3H-labeled endotoxin from the membrane was performed, resulting in the removal of endotoxin associated with the membrane by alcoholic alkali at 78% efficiency.     

Lipids in membrane protein structures

This review describes the recent knowledge about tightly bound lipids in membrane protein structures and deduces general principles of the binding interactions. Bound lipids are grouped in annular, nonannular, and integral protein lipids. The importance of lipid binding for vertical positioning and tight integration of proteins in the membrane, for assembly and stabilization of oligomeric and multisubunit complexes, for supercomplexes, as well as their functional roles are pointed out. Lipid binding is stabilized by multiple noncovalent interactions from protein residues to lipid head groups and hydrophobic tails. Based on analysis of lipids with refined head groups in membrane protein structures, distinct motifs were identified for stabilizing interactions between the phosphodiester moieties and side chains of amino acid residues. Differences between binding at the electropositive and electronegative membrane side, as well as a preferential binding to the latter, are observed. A first attempt to identify lipid head group specific binding motifs is made. A newly identified cardiolipin binding site in the yeast cytochrome bc(1) complex is described. Assignment of unsaturated lipid chains and evolutionary aspects of lipid binding are discussed.     

Biochemical signal transmitted by Fc receptor for immunoglobulin G2a of a murine macrophage-like cell line, P388D1: mode of activation of adenylate cyclase mediated by immunoglobulin G2a binding proteins

The effects of immunoglobulin G2a binding proteins isolated from P388D1 cells on adenylate cyclase of cyc- cells were investigated to explore a potential role of Fc gamma 2a receptor in the activation of the adenylate cyclase system. Immunoglobulin G (IgG) binding proteins obtained from the detergent lysate of P388D1 cells by affinity chromatography on IgG-Sepharose were separated into two fractions (denoted as IgG-B1 and IgG-B2) by Sephadex G-100 gel filtration in the presence of 6 M urea. Polyacrylamide gel electrophoretic analysis in the presence of sodium dodecyl sulfate revealed that the major component in the IgG-B1 fraction was a protein of molecular weight near 50 000, whereas the IgG-B2 fraction contained two major components of molecular weight near 25 000 and 17 000. Both IgG-B1 and -B2 proteins can be inserted into liposome consisting of phosphatidylcholine and phosphatidylethanolamine. Liposomes containing IgG-B1 proteins effectively inhibited EA2a, but not EA2b, rosetting by either S49 or P388D1 cells, suggesting their proper orientation within liposome, whereas IgG-B2-containing liposome failed to do so. Simultaneous fusion of the liposomes containing IgG-B1 and -B2 proteins with guanine nucleotide binding stimulatory (G/F) protein/Fc gamma 2aR-deficient cyc- cells resulted in the formation of the hybrid membrane whose adenylate cyclase responds to immune complex formed with IgG2a-subclass antibody (IC2a) by about a 2.7-fold increase in the activity over the control (hybrid membrane between cyc- cells and liposome containing no protein). The response appeared to be specific, since IC2b failed to stimulate the enzymatic activity of this hybrid membrane. Furthermore, IgG-B1 and -B2 proteins were able to confer their activating effects on the enzyme only in concert, since the fusion of liposomes containing either type of protein alone with cyc- cells did not result in the activation of adenylate cyclase of cyc- membrane. IgG-B1 and -B2 proteins could also confer their activating effects in concert to the enzyme in cholate-solubilized forms. Such activation was dependent on the concentration of IC2a, suppressed by the chelating agent ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, and significantly inhibited by trifluoperazine, suggesting potential involvement of Ca2+ and calmodulin in the activating process.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of lipid unsaturation on the binding of native and a mutant form of cytochrome b5 to membranes

The partitioning of native cytochrome b5 and a mutant form, where Trp-108 and Trp-112 were both replaced by Leu, into small unilamellar lipid vesicles was examined. The vesicles were made from phosphatidylcholines containing mono- and di-unsaturated acyl chains. As these amphipathic proteins self-associate in aqueous solution, the binding was not monitored by a simple lipid titration experiment but by an exchange assay using fluorescence quenching by brominated lipids. Each protein had a greater affinity for lipids containing mono-unsaturated chains than for vesicles containing di-unsaturated chains, and the affinities of both proteins increased in buffers of higher ionic strength. The native protein had a higher affinity than the mutant protein for all vesicles; the ratio of the affinities was relatively constant at approximately 30. This corresponds to a difference in the free energy of partitioning of 2 kcal mol(-)(1). The fluorescence quantum yields of both proteins were much lower in lipids with di-unsaturated chains whereas a similar lowering was not seen with a simple Trp compound. These data suggest that the decreased membrane hydrophobicity seen by the proteins in di-unsaturated membranes is not an inherent property of the bilayer but is induced by the insertion of the protein. Further, the similar behavior of the two proteins suggests this modulation is not sensitive to the amino acid side chains of the inserted domain.     

New Insights into the Protein Import Machinery of the Chloroplast's Outer Envelope

A large number of plastid localized proteins are post-translationally imported as precursor proteins from the cytosol into the organelle. Recognition and translocation is accomplished by a subset of chloroplast envelope proteins, which were identified by different but complementary methods. The o uter e nvelope p roteins OEP 86, OEP 75, OEP 70 (a heat shock cognate 70 homologue) and OEP 34 are clearly involved in the import event and can be isolated as one functionally active translocation unit. For three of these proteins cDNA clones have been very recently obtained, namely OEP 86, OEP 75 and OEP 34. OEP 86 seems to be a precursor protein receptor which could be regulated by GTP binding and ATP-dependent phosphorylation-dephosphorylation. OEP 75 is part of the translocation pore traversing the membrane in multiple β-sheets. OEP 34 is tightly associated with OEP 75. It represents a new type of GTP-binding protein which possesses endogenous GTPase activity. Multiple GTP binding and hydrolysis cycles as well as protein phosphorylation-dephosphorylation events might, therefore, regulate the interaction of a precursor protein with the translocation machinery of the outer envelope, making it very distinct from the mitochondrial outer membrane system. Further proteins of the inner envelope membrane, namely IEP 97 and IEP 36, have been implied to function in the translocation event. These recent data allow not only identification of the players in the game but also speculation about mechanisms and regulation of translocation.     

The construction of a zwitterionic PVDF membrane surface to improve biofouling resistance

Biofouling of membrane surfaces by the attachment of microorganisms is one of the major obstacles for ensuring the effectiveness of membrane separation processes. This work presents the construction of a zwitterionic PVDF membrane surface with improved resistance to biofouling. An amphiphilic copolymer of poly(vinylidene fluoride)-graft-poly(N,N-dimethylamino-2-ethylmethacrylate) (PVDF-g-PDMAEMA) was first synthesized via radical graft copolymerization and then the flat membrane was cast with immersed phase inversion. The PDMAEMA side chains tended to aggregate on the membrane surface, pore surface and internal pore channel surface, and were converted with 1,3-propane sultone (1,3-PS) to yield a zwitterionic membrane surface. A higher conversion of PDMAEMA chains and distribution of zwitterions were obtained using a longer treatment time. A biofouling assay indicated that incorporation of zwitterions suppressed the adsorption of extracellar polymer substances and the adhesion of Escherichia coli bacterial cells to the membrane surface, endowing the membrane with a high flux recovery and biofouling resistance in the filtration process.