Proteomics is one of the most important issues in the post-genomic area, because it can greatly contribute to identifying protein biomarkers for disease diagnosis and drug screening. Protein array is a key technology for proteome researches and has been analyzed by various methods including fluorescence, mass spectrometry, atomic force microscopy and surface plasmon resonance (SPR). SPR biosensor is a promising technology in proteomics, since it has various advantages including real-time measurement of biomolecular interactions without labeling and the simple optical system for the device. SPR biosensors have a strong potential for analyzing proteomes by SPR imaging and SPR spectroscopic imaging, even though the challenge is to produce proteins on a proteomic scale.

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We have investigated whether surface plasmon resonance (SPR) sensors based on the wavelength interrogation are able to analyze protein interactions on protein arrays. The spectral SPR sensor was self-constructed and its detection limit, expressed as the minimal refractive index variation, was calculated to be 6.6x10(-5) with the signal fluctuation of 1.0x10(-5). The protein array surface was modified by a mixed thiol monolayer to immobilize proteins. Protein arrays were analyzed by the line-scanning mode of the SPR sensor, which scanned every 100 microm along the central line of array spots and the scanned results were presented by color spectra from blue to red. Glutathione S-transferase (GST)-rac1 caused a concentration-dependent increase of SPR wavelength shift on protein arrays. The surface structure of the protein arrays was analyzed by atomic force microscopy. Specific interactions of antigens with antibodies were analyzed on the protein arrays by using three antibodies and eight proteins. These results suggest that the wavelength interrogation-based SPR sensor can be used as the biosensor for the high-throughput analysis of protein interactions on protein arrays.

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We modified gold arrays with a glutathione (GSH) surface, and investigated high-throughput protein interactions with a spectral surface plasmon resonance (SPR) biosensor. We fabricated the GSH exterior on gold surfaces by successive modification with aminoethanethiol, 4-maleimidobutyric acid N-hydroxysuccinimide ester and GSH. We immobilized GST-Rac1, GST-RhoA, the GST-Rho-binding domain of rhotekin and the GST-p21-binding domain of PAK1 onto the GSH surface, and observed specific antigen-antibody interactions on the GST-fusion protein arrays. We determined the expression of GST-fusion proteins in Escherichia coli on the GSH surface with the SPR biosensor. We then analyzed the interactions of tissue transglutaminase (tTGase), a Ca2+-dependent enzyme, with RhoA and Rac1 on the GST-fusion protein arrays with the SPR biosensor. We found that tTGase interacted with RhoA and Rac1 in a Ca2+-dependent manner, indicating that the interactions were dependent on tTGase activity. In addition, transamidation of Rac1 by tTGase was dependent on Ca2+ concentration. We obtained similar results with GST pull-down assays. Thus, protein arrays prepared on the GSH surface provide a useful system for the high-throughput analysis of GST-fusion protein expression and activity-dependent protein interactions with the spectral SPR biosensors.