Bio-Rad launches protein interaction analyser

The new analyser, the ProteOn XPR36, combines surface plasmon resonance (SPR) with a CCD detector and a high-throughput fluidics system to allow the rapid and accurate collection of data about protein interactions. Virtually every cellular process depends on protein interactions, including DNA replication and transcription, protein modification and secretion, cell cycle control, signal transduction and gene expression. This makes the analysis of protein interactions an extremely valuable area of research. The array system has been designed to alleviate the bottlenecks when conducting antibody screening and ranking, kinetic characterisation of protein interactions, protein interface mapping and small molecule screening. The parallel processing allows the fast and efficient analysis of multiple protein interactions as well as 'one shot kinetics,' a method of kinetic analysis of an analyte series without the need for regeneration. The system also allows high throughput screening and comparative analysis of multiple samples and the rapid optimisation of experimental parameters by allowing analysis of multiple parameters in a single run. According to Dr Renee LeMaire-Adkins, marketing manager for the Protein Interaction Technology division at Bio-Rad Laboratories, the new instrument allows data for 180 interactions to be collected in an hour. "Customers we have worked with say that they can now do in two hours what would previously have been a week's work,"​ she said. "Scientists that we've spoken to estimate they previously spent up to 50 per cent of their time on process optimisation - by bringing microfluidic multiplexing to SPR they can test more parameters at once than in a sequential approach. It also allows them to do one shot kinetics experiments."​ The XPR36 overcomes the limitations of more conventional SPR methods by providing high throughput optimisation of experimental conditions in a 6 x 6 array. A two-dimensional CCD image is generated of the entire sensor chip, allowing the response from all 36 interactions to be measured simultaneously. A complete SPR curve for each interaction and reference spot on the chip can then be plotted from the data. The binding of an analyte molecule to a chosen ligand bound to the surface of the sensor chip causes a shift in the SPR curve proportional to the change near the chip surface. For example, as a protein in solution binds to the immobilised ligand, the refractive index near the sensor surface increases, leading to a shift in the SPR angle. When the protein solution is replaced with a solution without the protein, the protein dissociates leading to a decrease in the refractive index and the SPR angle shift There are 42 reference spots in between the flow channels, which are not exposed to activation or ligand immobilisation but are exposed to the analyte flow making them analogous to a reference channel. The 6 by 6 interaction array is generated by first lowering the multichannel module (MCM) on to the sensor chip surface which forms six channels in which a set of six different ligand samples can be immobilised. The MCM is then lifted up before a second set of channels is created at 90^o​ to the first where up to six analyte solutions can be injected in parallel. The response at each of the interaction spots at the cross-section between the two channels can then be measured, generating 36 sensorgrams, which can be normalised against the reference spots. The fluidics system allows a smooth, constant flow of sample and buffer solutions for the accurate measurement of binding kinetics. The measurement of multiple conditions in parallel allows the process of optimising the protocols for immobilisation and binding reactions can be conducted quickly and efficiently as well as allowing the screening and comparative analysis of multiple samples, such as those encountered in immunogenicity testing. Various technical notes have been published by the company to aid researchers using the instrument to gain results quickly and efficiently across a range of applications such as the determination of the kinetic rate constant of a reaction, the analysis of multiple antigen-antibody pairs, as well as ways to optimise the binding of proteins to the sensor chip and the optimisation of kinetics runs.