Polycationic Surface Research Articles

Plant cell wall patterning and expansion mediated by protein-peptide-polysaccharide interaction.

Assembly of cell wall polysaccharides into specific patterns is required for plant growth. A complex of RAPID ALKALINIZATION FACTOR 4 (RALF4) and its cell wall-anchored LEUCINE-RICH REPEAT EXTENSIN 8 (LRX8)-interacting protein is crucial for cell wall integrity during pollen tube growth, but its molecular connection with the cell wall is unknown. Here, we show that LRX8-RALF4 complexes adopt a heterotetrametric configuration in vivo, displaying a dendritic distribution. The LRX8-RALF4 complex specifically interacts with demethylesterified pectins in a charge-dependent manner through RALF4's polycationic surface. The LRX8-RALF4-pectin interaction exerts a condensing effect, patterning the cell wall's polymers into a reticulated network essential for wall integrity and expansion. Our work uncovers a dual structural and signaling role for RALF4 in pollen tube growth and in the assembly of complex extracellular polymers.

Contact-Biocide TiO2 Surfaces by Surface-Initiated Atom Transfer Radical Polymerization with Chemically Stable Phosphonate Initiators.

Surface-initiated atom transfer radical polymerization (SI-ATRP) is a powerful tool for grafting functional polymers from metal surfaces. It depends on the immobilization of suitable initiators on the surface before radical polymerization. Herein, we report a set of bifunctional initiators bearing a phosphonic acid group for surface binding and a bromoisobutyramide moiety for SI-ATRP. We have analyzed the impact of the connecting alkyl spacers on the grafting process of (vinylbenzyl)trimethylammonium chloride (VBTAC) from titanium as a base material. The thickness of the grafted polymer increased with the spacer length of the initiator. We obtained chemically stable polycationic surfaces with high charge densities of ∼1016 N+/cm2 leading to efficient contact activity of modified titanium coupons against S. aureus. Notably, SI-ATRP grafting was efficient with VBTAC as a styrene-derived ammonium compound. Thus, the reported protocol avoids post-grafting quaternization with toxic alkylating reagents.

Polycationic Surfaces Promote Whole-Cell Immobilization and Induce Microgranulation of Clostridium saccharoperbutylacetonicum N1-4 for Enhanced Biobutanol Production.

Immobilization is a common strategy used to protect microbial cells to improve the performance of bioprocesses. However, the interaction mechanism between the cells and the immobilization material is generally poorly understood. In this study, we employed natural polysaccharide-based materials as immobilization carriers for clostridial fermentation in an attempt to enhance the production of butanol (a valuable biofuel/biochemical but highly toxic to the host cells) and meanwhile elucidate the interaction mechanisms related to immobilization. The utilization of chitosan powder as the immobilization carrier enhanced butanol productivity by 97% in the fermentation with Clostridium saccharoperbutylacetonicum N1-4 and improved butanol titer by 21% in the fermentation with Clostridium beijerinckii NCIMB 8052. Additionally, analogue derivatives using microcrystalline cellulose (MCC) and cotton cationized on the surface with 3-chloro-2-hydroxypropyltrymethylammonium (CHPTA) and 2-chloro-N,N-diethylaminoethyl chloride (DEAEC) were prepared and used as immobilization carriers for similar fermentation conditions. The CHPTA derivatives showed slightly increased production of butanol and total solvent with C. saccharoperbutylacetonicum. Overall, our results indicated that the interaction between the cell and the carrier material occurs through a double mechanism involving adsorption immobilization and induced aggregation. This work provides insights concerning the effects of the chemical properties of the carrier material (such as the cation density and surface area) on fermentation performance, enabling a better understanding of the interaction between bacterial cells and the cationic materials. The derivatization strategies employed in this study can be applied to most cellulosic materials to modulate the properties and enhance the interaction between the cell and the carrier material for immobilization, thus improving the bioprocess performance.

All-Aqueous Microfluidics Fabrication of Multifunctional Bioactive Microcapsules Promotes Wound Healing.

Wound healing involves multiple stages of body responses, including hemostasis, inflammation, cell proliferation, and tissue remodeling. New material design satisfying all demands throughout different stages of wound healing is cherished but rarely discussed. Here we introduce all-aqueous multiphase microfluidics as a novel strategy to fabricate self-assembled, multifunctional alkylated chitosan/alginate microcapsules (SAAMs) as novel therapeutic materials for rapid blood coagulation and wound healing. SAAMs are structurally distinguished by their ultrathin shells with polycationic surface for rapid activation of clotting cascade and their internal porous dextran-rich cores for fast absorption of blood and exudate. These features endow SAAMs with excellent hemostatic properties for acute hemorrhage. Moreover, the alkylated chitosan within the microcapsules exhibits persistent antimicrobial activities against bactericidal infections due to their amphiphilic and cationic surfaces. Besides, cytokines can be safely loaded into the organic-solvent-free microcapsules and released precisely to promote the proliferation of epidermal cells, supporting the subsequent development of granulation tissue and suppression of inflammation in the last stages of wound healing. With the ability to fabricate size-tailored soft microcapsules and to realize time-sequential functions for tissue repairing, the presented "all-aqueous microfluidics generation of multifunctional bioactive SAAMs" create a versatile and robust paradigm for wound treatment.

Chitin and Chitosan: Prospective Biomedical Applications in Drug Delivery, Cancer Treatment, and Wound Healing.

Chitin and its derivative chitosan are highly abundant polymers in nature, appearing in both the shells and exoskeletons of various marine and non-marine species. Since they possess favorable properties, such as biocompatibility, biodegradability, non-toxicity, and non-immunogenicity, they have gained recent attention due to their enormous potential biomedical applications. The polycationic surface of chitosan enables it to form hydrogenic and ionic bonds with drug molecules, which is one of its most useful properties. Because chitosan is biocompatible, it can therefore be used in drug delivery systems. The development of chitosan-based nanoparticles has also contributed to the significance of chitin as a drug delivery system that can deliver drugs topically. Furthermore, chitin can be used in cancer treatment as a vehicle for delivering cancer drugs to a specific site and has an antiproliferative effect by reducing the viability of cells. Finally, chitosan can be used as a wound dressing in order to promote the faster regeneration of skin epithelial cells and collagen production by fibroblasts. As discussed in this review, chitin and chitosan have diverse applications in the medical field. Recognizing the biomedical applications of these two polymers is essential for future research in tissue engineering and nanobiotechnology.

Viral Transduction Enhancing Effect of EF‐C Peptide Nanofibrils Is Mediated by Cellular Protrusions

AbstractSelf‐assembling peptide nanofibrils (PNF) have gained increasing attention as versatile molecules in material science and biomedicine. One important application of PNF is to enhance retroviral gene transfer, a technology that has been central for gene therapy approaches. The best‐investigated and commercially available PNF is derived from a 12‐mer peptide termed EF‐C. The mechanism of transduction enhancement depends on the polycationic surface of EF‐C PNF, which bind to the negatively charged membranes of viruses and cells, thereby overcoming electrostatic repulsions and increasing virion attachment and fusion. To better understand how EF‐C PNF interact with the cell surface, scanning electron and time‐lapse confocal microscopy were performed. The fibrils are found to be actively engaged by cellular protrusions such as filopodia. Consequently, chemical suppression of protrusion formation abrogates fibril binding and virion delivery to the cell surface of immortalized and primary T cells. Vice versa, induction of plasma membrane blebs result in increased fibril binding. Thus, the mechanism of PNF‐mediated viral transduction enhancement involves an active engagement of virus‐loaded fibrils by cellular protrusions, which may explain its superior performance over soluble transduction enhancers.

Biodegradable Anti-Biofilm Fiber-Membrane Ureteral Stent Constructed with a Robust Biomimetic Superhydrophilic Polycationic Hydration Surface Exhibiting Synergetic Antibacterial and Antiprotein Properties.

The biofouling of ureteral stents and subsequent urinary tract infections mainly come from the adsorption and adhesion of proteins and microorganisms and their ensuing proliferation. Although general polycationic surfaces in implants have good antibacterial activities, they suffer from limited durability due to severe protein and bacterial adsorption. Here, a biodegradable and anti-biofilm fiber-membrane structured ureteral stent (FMBUS) with synergetic contact-killing antibacterial activity and antiprotein adsorption is described. The stent is prepared by generating hyperbranched poly(amide-amine)-grafted polydopamine microparticles (≈300nm) on the surface of fibers by in situ polymerization and Schiff base reactions. The biomimetic surface endows the FMBUS with a positive charge (+21.36mV) and superhydrophilicity (water contact angle: 0°). As a result, the stents fulfilled the following functions: i) reduced attachment of host protein due to superhydrophilicity (Lysozyme: 92.1%; human serum albumin: 39.4%); ii) high bactericidal activities against contact pathogenic bacteria (contact-killing rate: 99.9999% for both E. coli and S. aureus; antiadhesion rate: 99.2% for E. coli and 99.9999% for S. aureus); iii) biocompatibility in vitro (relative growth rate of L929: >90% on day 3) and in vivo; and iv) gradient biodegradability to avoid a second surgery of stent extraction 1-2 weeks after implantation.

Polyelectrolyte Substrate Coating for Controlling Biofilm Growth at Solid–Air Interface

AbstractBecause bacteria–surface interactions play a decisive role in bacteria adhesion and biofilm spreading, it is essential to understand how biofilms respond to surface properties to develop effective strategies to combat them. Polyelectrolyte coating is a simple and efficient way of controlling surface charge and energy. Using polyelectrolytes of various types, with different molecular weights and polyelectrolyte solutions of various pH provides a unique approach to investigate the interactions between biofilms and their substrate. Here, the formation of Escherichia coli biofilms at a solid–air interface is explored, whereby charge and interfacial energy are tuned using polyelectrolyte coatings on the surface. Cationic coatings are observed to limit biofilm spreading, which remain more confined when using high molecular weight polycations. Interestingly, biofilm surface densities are higher on polycationic surfaces despite their well‐studied bactericidal properties. Furthermore, the degree of polyelectrolyte protonation also appears to have an influence on biofilm spreading on polycation‐coated substrates. Finally, altering the interplay between biomass production and surface forces with polyelectrolyte coatings is shown to affect biofilm 3D architecture. Thereby, it is demonstrated that biofilm growth and spreading on a hydrogel substrate can be tuned from confined to expanded, simply by coating the surface using available polyelectrolytes.

Counterion‐Dictated Self‐Cleaning Behavior of Polycation Coating upon Water Action: Macroscopic Dissection of Hydration of Anions

AbstractThe counterions of polydiallyldimethylammonium (PDADMA) coatings were altered by incubation in aqueous solutions of different electrolytes. Oil de‐wetting on the resulting polycationic surfaces upon water action exhibited a straightforward connection with the Jones–Dole viscosity B‐coefficient (Bη) sign of surface counteranions. Upon water action, surface counteranions with negative Bη render PDADMA coatings oil‐adhering, but those with positive Bη furnish PDADMA coatings with excellent self‐cleaning. The oil‐adhering PDADMA surfaces can become self‐cleaning upon water action in response to the Bη of surface counteranions sign‐switching with increasing water temperature. Courtesy of surface counter‐anions with Bη>0, self‐cleaning PDADMA coatings enable not only conversion of conventional meshes into self‐cleaning membranes for oil/water separation, but also regioselective maneuver of oil flow on polycationic surfaces according to the Bη sign of surface counteranions patterned atop.

Counterion-Dictated Self-Cleaning Behavior of Polycation Coating upon Water Action: Macroscopic Dissection of Hydration of Anions.

The counterions of polydiallyldimethylammonium (PDADMA) coatings were altered by incubation in aqueous solutions of different electrolytes. Oil de-wetting on the resulting polycationic surfaces upon water action exhibited a straightforward connection with the Jones-Dole viscosity B-coefficient (Bη) sign of surface counteranions. Upon water action, surface counteranions with negative Bη render PDADMA coatings oil-adhering, but those with positive Bη furnish PDADMA coatings with excellent self-cleaning. The oil-adhering PDADMA surfaces can become self-cleaning upon water action in response to the Bη of surface counteranions sign-switching with increasing water temperature. Courtesy of surface counter-anions with Bη>0, self-cleaning PDADMA coatings enable not only conversion of conventional meshes into self-cleaning membranes for oil/water separation, but also regioselective maneuver of oil flow on polycationic surfaces according to the Bη sign of surface counteranions patterned atop.

In vitro evaluation of contact-active antibacterial efficacy of Ti-Al-V alloys coated with the antimicrobial agent PHMB

Immobilized polycationic substances on biomaterial surfaces kill adhering bacteria upon contact and are considered a promising non-antibiotic alternative. Unfortunately, there is no generally accepted in vitro method for quantitatively evaluating the antibacterial efficacy of contact-active non-leachable antimicrobial surfaces. Moreover, guidelines of generally accepted international industrial standards do not reflect the basic principle of bacterial contamination and/or are performed in the presence of a solid covering material. Therefore, in the present study, six bacterial adherence tests on non-porous surfaces with no covering material were compared with respect to their efficacy and reproducibility, as well as to evaluate the bactericidal contact-killing of relevant device-associated slime-producing bacteria using antimicrobially coated Ti6Al4V surfaces with positively-charged poly(hexamethylene biguanide) hydrochloride (PHMB). After direct bacterial inoculation to simulate a perioperative infection, non-leaching PHMB reacts bactericidally against the slime-producing bacteria Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa after surface contact. The 6-h drop technique was found to be a suitable method to quantitatively evaluate contact-active antibacterial surfaces. Adjunctively, however, damage of bacterial membrane integrity should be confirmed by LIVE/DEAD staining and the presence of non-leaching agents. Statement of SignificanceUnintentional perioperative bacterial adhesion to implant surfaces can generate biomaterial-associated infections. Adhered bacteria produce biofilms that protect them from antibiotic attack, which may be complicated by possible antibiotic resistance. Polycationic surfaces can prevent such unwanted biofilm formation by killing bacteria upon initial contact. Unfortunately, no reliable in vitro methods exist to evaluate the efficacy of contact-active antimicrobial surfaces. In this study, we show that the 6-h drop technique may be a suitable method to evaluate positively-charged contact-killing surfaces. Identification of suitable screening assays for evaluating the bactericidal efficacy of non-leachable antimicrobial agents will greatly improve this newly developing field as a prophylactic alternative to postoperative treatment of implant-associated infections by antibiotics.

A simultaneous grafting/vinyl polymerization process generates a polycationic surface for enhanced antibacterial activity of bacterial cellulose

Bacterial cellulose (BC) is a biosynthesized carbohydrate polymer with excellent biocompatibility and water holding capability. However, it lacks an inherent antibacterial activity that has limited its in-depth biomedical applications. This study investigated a novel strategy of adopting a simultaneous process to chemically anchor a quaternary ammonium salt (R-N(CH3)+) with a special vinyl group (2-methacryloyloxyethyl trimethylammonium chloride, METAC) onto the BC, and meanwhile, enhance the density of (R-N(CH3)+) via free radical vinyl polymerization. The results have confirmed the transition of BC surface from a negatively-charged surface to a polycationic surface via such a simultaneous reaction. As compared to chitin film (a representative of R-NH3+), the resulting METAC-grafted BC (a representative of high-density R- N(CH3)+) acquired excellent water absorbability (40 times of dry weight of the BC), 99% antibacterial activity against Escherichia coli and Staphylococcus aureus, a satisfactory in-vitro biocompatibility, and a better in-vivo wound healing outcome with an excellent in-vivo antibacterial efficacy. This study has exhibited potential in utilizing a facile method to prepare a bio-safe, adaptive antibacterial surface for various biomedical applications.

Photo-responsive membrane surface: Switching from bactericidal to bacteria-resistant property

In this paper, a photo-responsive bactericidal and bacteria-resistant membrane was successfully prepared via the integration of atom transfer radical polymerization (ATRP) and click chemistry. Azide-functionalized polycationic poly (N, N-dimethyl-N-(2-(methacryloyloxy)ethyl)-N-((2-nitrobenzyl)oxy)-2-oxoethanaminium bromide) (PDMAEMA-NBE) was synthesized by ATRP. Then, the PDMAEMA-NBE was clicked on alkynyl-functionalized polyethersulfone (PES) membrane surface, and proved by X-ray photoelectron spectrometer (XPS). Upon UV irradiation, the polycationic surface would switch to polyzwitterionic one. Before and after the irradiation, the zeta potentials of the surface altered from +14.7 to −3.8mV, and the water contact angle decreased from 64.0° to 52.7°. The polycationic surface exhibited excellent bactericidal property and the dead bacteria could detach from the polyzwitterionic surface induced by the subsequent UV irradiation. It demonstrated that the designing of photo-responsive membrane surface could be a new strategy for antibacterial adhesion.

A Positively Charged Surface Triggers Coagulation Activation Through Factor VII Activating Protease (FSAP).

Contact between biomedical materials and blood often initiates undesirable pro-coagulant and pro-inflammatory processes. On negatively charged materials, blood coagulation is known to be triggered through autoactivation of Factor XII, while activation on cationic surfaces follows a distinct and so far enigmatic mechanism. Because Factor VII activating protease (FSAP) is known to be activated on positively and on negatively charged macromolecules in plasma, we have investigated its interaction with charged biomaterials and its consequences for coagulation. Several activation processes in blood and plasma were characterized after contact with material surfaces with varied charge. FSAP was found to be exclusively activated by the positively charged surfaces polyethylenimine (PEI) and poly-l-lysine (PLL), not by the negatively charged glass or self-assembled monolayer with carboxyl group termination (SAM-COOH), as well as uncharged (Teflon AF) surfaces. Whole blood incubation on PEI showed that this activation was concomitant with coagulation as determined by thrombin and fibrin formation, which was high for glass (F1+2, 138 nM) and PEI (F1+2, 44 nM) but low for Teflon AF (F1+2, 3.3 nM) and SAM COOH (F1+2, 5.8 nM). Contact phase inhibitor diminished coagulation to background levels for all surfaces except PEI (F1+2: ^PEI 43 to 25 nM; glass, 58 to 1.5 nM) indicating that coagulation activation is not dependent on FXII activation on the PEI surface. A decisive role of endogenous FSAP for coagulation however was confirmed with the use of FSAP inhibitory antibodies which showed no influence on Teflon AF, glass and SAM COOH but diminished F1+2 on PEI to less than 50%. We propose that FSAP activation could be a novel mechanism of surface-driven coagulation. An inhibition of this protease might improve hemocompatibility of cationic surfaces and therefore facilitate the application of polycationic surfaces in blood.

Elastic Modulus Dependence on the Specific Adhesion of Hydrogels

AbstractMechanosensitivity in biology, e.g., cells responding to material stiffness, is important for the design of synthetic biomaterials. It is caused by protein receptors able to undergo conformational changes depending on mechanical stress during adhesion processes. Here the elastic modulus dependence of adhesive interactions is systematically quantified using ligand–receptor model systems that are generally not thought to be mechanosensitive: biotin–avidin, mannose–concanavalin A, and electrostatic interactions between carboxylic acids and polycationic surfaces. Interactions are measured by microgel sensors of different stiffness adhering to surfaces presenting a corresponding binding partner. Adhesion is generally decreased for softer microgels due to reduced density of binding partners. Density‐normalized data show that low‐affinity carbohydrate ligands exhibit reduced binding in softer networks, probably due to increased network conformational entropy. However, in case of stronger interactions with large interaction range (electrostatic) and large lifetime (biotin–avidin) density normalized adhesion is increased. This suggests compensation of entropic repulsion for softer networks probably due to their increased mechanical deformation upon microgel adhesion and enhanced cooperative binding. In essence, experiments indicate that soft interacting polymer materials exhibit entropic repulsion, which can be overcome by strongly interacting species in the network harnessing network flexibility in order to increase adhesion.

Hierarchical Polymer Brushes with Dominant Antibacterial Mechanisms Switching from Bactericidal to Bacteria Repellent.

Although polycationic surfaces have high antimicrobial efficacies, they suffer from high toxicity to mammalian cells and severe surface accumulation of dead bacteria. For the first time, we propose a surface-initiated photoiniferter-mediated polymerization (SI-PIMP) strategy of constructing a "cleaning" zwitterionic outer layer on a polycationic bactericidal background layer to physically hinder the availability of polycationic moieties for mammalian cells in aqueous service. In dry conditions, the polycationic layer exerts the contact-active bactericidal property toward the adherent bacteria, as the zwitterionic layer collapses. In aqueous environment, the zwitterionic layer forms a hydration layer to significantly inhibit the attachment of planktonic bacteria and the accumulation of dead bacteria, while the polycationic layer kills bacteria occasionally deposited on the surface, thus preserving the antibacterial capability for a long period. More importantly, the zwitterionic hydrated layer protects the mammalian cells from toxicity induced by the bactericidal background layer, and therefore hierarchical antibacterial surfaces present much better biocompatibility than that of the naked cationic references. The dominant antibacterial mechanism of the hierarchical surfaces can switch from the bactericidal efficacy in dry storage to the bacteria repellent capability in aqueous service, showing great advantages in the infection-resistant applications.

Reducing infectivity of HIV upon exposure to surfaces coated with N,N‐dodecyl, methyl‐polyethylenimine

The infectivity of high-titer, cell-free HIV in culture media and human milk is rapidly reduced upon exposure to polyethylene slides painted with the linear hydrophobic polycation N,N-dodecyl,methyl-polyethylenimine (DMPEI). Accompanying viral p24 protein and free viral RNA analysis of solutions exposed to DMPEI-coated surfaces suggests that virion attachment to the polycationic surface and its subsequent inactivation are the likely mechanism of this phenomenon.

Broad Based Tissue Uptake of Polycationic Near-Infrared Polymeric Nanoparticles in Living Mice

A near infrared (NIR) fluorescent polymeric nanoparticle, commercialized under the name X-Sight 761 (X761), was tested for compatibility with pre-clinical in vivo imaging applications. In one experiment, an optical clearance profile was obtained by performing whole animal fluorescence imaging over the course of 48 hours on mice injected intravenously with X761. In a second trial, a temporal biodistribution was assessed by conducting necropsy and ex vivo analysis of X761 tissue accumulation at selected time points over a 48 hours period after i.v. injection. Taken together, the data demonstrate a sustained distribution of X761 into all major tissues over the time course, with an extremely low net clearance from the animal. This unique behavior is attributed to cell uptake mediated by the polycationic surface of X761. These properties negate the use of X761 as a reporter within a classical targeted molecular probe construct, in which selective concentration at a target site and rapid clearance from background tissues are needed to develop contrast. Nevertheless, the brightness and stability of X761 is well suited for a range of other applications, ranging from broad based in vivo drug delivery to in vitro fluorescence assays.

On-chip solid phase extraction and enzyme digestion using cationic PolyE-323 coatings and porous polymer monoliths coupled to electrospray mass spectrometry

We evaluate the compatibility and performance of polymer monolith solid phase extraction beds that incorporate cationic charge, with a polycationic surface coating, PolyE-323, fabricated within microfluidic glass chips. The PolyE-323 is used to reduce protein and peptide adsorption on capillary walls during electrophoresis, and to create anodal flow for electrokinetically driven nano-electrospray ionization mass spectrometry. A hydrophobic butyl methacrylate-based monolithic porous polymer was copolymerized with an ionizable monomer, [2-(methacryloyloxy)ethyl] trimethylammonium chloride to form a polymer monolith for solid phase extraction that also sustains anodal electroosmotic flow. Exposure of the PolyE-323 coating to the monolith forming mixture affected the performance of the chip by a minor amount; electrokinetic migration times increased by ∼5%, and plate numbers were reduced by an average of 5% for proteins and peptides. 1-mm long on-chip monolithic solid phase extraction columns showed reproducible, linear calibration curves ( R 2 = 0.9978) between 0.1 and 5 nM BODIPY at fixed preconcentration times, with a capacity of 2.4 pmol or 0.92 mmol/L of monolithic column for cytochrome c. Solution phase on-bed trypsin digestion was conducted by capturing model protein samples onto the monolithic polymer bed. Complete digestion of the proteins was recorded for a 30 min stop flow digestion, with high sequence coverage (88% for cytochrome c and 56% for BSA) and minimal trypsin autodigestion product. The polycationic coating and the polymer monolith materials proved to be compatible with each other, providing a high quality solid phase extraction bed and a robust coating to reduce protein adsorption and generate anodal flow, which is advantageous for electrospray.

An electrostatic switch displaces phosphatidylinositol phosphate kinases from the membrane during phagocytosis

Plasmalemmal phosphatidylinositol (PI) 4,5-bisphosphate (PI4,5P(2)) synthesized by PI 4-phosphate (PI4P) 5-kinase (PIP5K) is key to the polymerization of actin that drives chemotaxis and phagocytosis. We investigated the means whereby PIP5K is targeted to the membrane and its fate during phagosome formation. Homology modeling revealed that all PIP5K isoforms feature a positively charged face. Together with the substrate-binding loop, this polycationic surface is proposed to constitute a coincidence detector that targets PIP5Ks to the plasmalemma. Accordingly, manipulation of the surface charge displaced PIP5Ks from the plasma membrane. During particle engulfment, PIP5Ks detached from forming phagosomes as the surface charge at these sites decreased. Precluding the change in surface charge caused the PIP5Ks to remain associated with the phagosomal cup. Chemically induced retention of PIP5K-gamma prevented the disappearance of PI4,5P(2) and aborted phagosome formation. We conclude that a bistable electrostatic switch mechanism regulates the association/dissociation of PIP5Ks from the membrane during phagocytosis and likely other processes.