lab fab
First DIBs on protocell networks Researchers assemble networks of primitive artificial cells that communicate through shared lipid bilayers.
L
MATTHEW HOLDEN
ike nosy neighbors passing along study electrically driven processes.” and screened against droplets containthe latest bits of juicy gossip, cells The researchers assembled DIB neting known αHL pore blockers that were constantly receive and transmit signals works in different configurations that fixed to opposing electrodes. Holden from each other and from the extracelfunctioned as wires, batteries, and light and colleagues plan to apply the DIB lular environment. Cellular communicasensors. By incorporating an anion-sesystem to the screening of medically reltion in the form of ion flow through gap lective HL mutant into DIBs, Holden evant ion channels. junctions or membrane pores underlies and colleagues constructed a “biobatHenry Lester at the California Inphysiological processes such as the firtery”—a DIB network that generated its stitute of Technology thinks that the ing of neurons and the coordination of own current by the net flow of Cl– ions. DIB networks show great promise for contractions in the heart. However, drug-screening applications, for the complex milieu of ions, signaling example, the screening of pharmamolecules, and membrane proteins ceutical candidates for beneficial in living cells complicates the study or detrimental interactions with of cellular communication. To simion channels. Lester says, “These plify these studies, Matthew Holden, bilayers can potentially serve as bioHagan Bayley, and David Needham sensors for molecules that interact at the University of Oxford (U.K.) with intracellular binding sites on and Duke University fabricated netmembrane channels, which have works of tiny, lipid-encased water been only indirectly accessible until droplets that mimic rudimentary now.” Dan Tawfik at the Weizmann cells (J. Am. Chem. Soc. 2007, 129, Institute of Science (Israel) says, 8650–8655). “The screening and assaying of The researchers created the “promembrane proteins are an area of tocells” by placing aqueous droplets biochemistry that has lagged behind into a mixture of oil and lipids. A because these proteins are not active monolayer surrounded each 200 nL (Left) Schematic of a DIB network. (Top right) DIB or folded in solution. This method droplet, forming an oversized “renetwork of droplets containing red or yellow dye. provides a cell-like compartment verse micelle”. After monolayer sta(Bottom right) Representation of HL pores in a DIB. in which membrane proteins can bilization, droplets were brought tobe incorporated and their activities gether so that adjacent lipid monolayers A light-sensing DIB was fabricated by monitored.” Lester and Tawfik agree fused to form a droplet-interface bilayer inserting the light-driven proton pump that DIB network assembly eventually (DIB). Ions, membrane pores, or other bacteriorhodopsin (BR) into DIBs. should be automated to allow highmolecules could then be included in the When the DIB network was irradiated throughput applications. droplets. The DIB networks were stable with green light, a sharp spike in curIn the future, researchers might be enough that an individual droplet could rent through the network was observed. able to make droplets containing an in be plucked from the network by an aga- Holden says, “There are engineered vitro expression system and a plasmid rose-coated wire, and another droplet BRs that are sensitive to different colors encoding a membrane protein of inter(perhaps containing different molecules) of light, so theoretically you could conest. Freshly produced membrane protein could be inserted in its place. struct large networks of droplets that would insert directly into the DIB, After incorporating the protein pore act as pixels in an imaging array.” skipping time-consuming and possibly staphylococcal -hemolysin (HL) into In addition to their use in protocell deactivating purification steps. “You DIBs, Holden and colleagues studied networks, the robust nature of the drop- could investigate proteins that cannetworks of interacting droplets by lets allows them to be used for memnot be purified in an active form from measuring the electrical current passing brane protein screening. Bilayers can standard protein expression systems,” through the bilayer between adjacent be formed, split apart, and re-formed, Holden says. “Insertion of freshly transdroplets or across multiple droplets. Ac- allowing a droplet to be sequentially lated proteins could be monitored by cording to Holden, “By arranging the contacted with opposing droplets in an conductance, possibly providing insights protocells into networks, we might be array. For example, a droplet loaded with into channel formation.” a able to build realistic model systems to αHL was attached to a mobile electrode —Laura Cassiday © 2007 AMERICAN CHEMICAL SOCIET Y
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