January 15, 2005
| As we start a new year, it is clear that the trend toward automation of both cell-based and proteomic assays will continue. Although genomic assays led the charge toward high-throughput science, new detection systems and formats are enabling the application of high-throughput techniques to proteins and cells.
Li-Cor Biotechnology recently adapted its Odyssey Imaging System to quantify proteins in a high-throughput cell-based assay. The company's new Aerius Automated Infrared Imaging System is designed for protein detection using infrared labeling of proteins in plate-based assays. "In-cell Westerns" use infrared dye-labeled secondary antibodies to directly monitor specific proteins in cells. The user can quantify total fluorescence from cells in each well — obviating time-consuming and error-prone steps such as lysate preparation and membrane transfer. Li-Cor's automated system includes a reader that can handle up to 30 microplates at a time. Two-color scanning allows for simultaneous detection of two protein targets, or the use of one channel for normalization to a control protein. The Aerius enables automatic or interactive analysis of scanned images. Li-Cor has also adapted the Odyssey platform to measure the internalization and recycling of G protein-coupled receptors (GPCRs).
The importance of membrane-associated proteins for signaling and cell communication makes them highly attractive targets for drug discovery. In a recent cover story in Nature, researchers reported how they made use of another important new high-throughput technology to establish the conditions for crystallization of integrin aIIbb3, a transmembrane protein linked to coronary artery thrombosis. This enabled the scientists to determine its three-dimensional structure, which should facilitate design of drugs against the protein. (See Xiao, T. et al. Nature 432, 59-67; 2004.)
SCREEN PASS: Hamamatsu's System 6000 does both fluorescent and luminescent kinetic measurements.
The researchers used Fluidigm's Topaz system (see Fully Equipped, Feb. 2003 Bio·IT World
). Integrins, like other membrane proteins and GPCRs, are difficult to express and crystallize. The Topaz system is a nanoscale chip-based device that requires far less protein and reagent per experiment than microliter-drop-based methods of crystallization.
Assays for protein activity are also being increasingly adapted to high-throughput format. With the success of the anti-cancer drug Gleevec, researchers have grown more interested in protein kinases as drug targets. Companies have introduced assays to measure these activities. A good example is QTL Biosystems' Lightspeed Kinase platform, which currently monitors four cancer-associated kinase targets: PKCa, Akt1, P38a, and Src. These assays do not require antibodies or radioactive labels, they are compatible with standard fluorescent instrumentation, and they can make use of either peptide or protein substrates. QTL intends to roll out nine new kinase assays in the coming months, with more planned throughout 2005. Stratagene's SignalScout kinase profiling system offers similar multiplexed kinase monitoring.
High-throughput science needs automated robotic systems to handle the workload, and there are myriad systems on the market. One of the newest arrivals is Hamamatsu's Fluorescence Drug Screening System 6000 — a modular, imaging-based plate reader for cellular assays, assay development, and high-throughput screening. An internal flexible robot, 96/384-well injectors, and two detection units allow both fluorescent and luminescent kinetic measurements. The system is ideal for applications such as measurement of cellular membrane potential, ion-channel fluorescence resonance energy transfer (FRET), or aequorin and flash luciferase assays.
Of course, no discussion of trends in high-throughput science is complete without mention of protein and antibody arrays. BD Clontech offers the Ab microarray, designed to profile as many as 500 intracellular proteins simultaneously on a single experiment. And Sigma-Aldrich's Panorama Ab microarrays allow users to assay nearly 250 proteins in key biological pathways.
Robert M. Frederickson is a science writer based in Seattle. E-mail: email@example.com.