Protein Microarrays - A Tool for the Post-Genomic Era

The human genome is sequenced and the challenges of understanding the function of the newly discovered genes have been addressed. For this purpose, high-throughput technologies have been developed that allow the monitoring of gene activity at the transcriptional level by analysis of complex expression patterns of a specific tissue. Differential gene expression can be most efficiently monitored by oligonucleotide or cDNA hybridization on DNA arrays. Recently, protein arrays are emerging to follow DNA chips as a tool to profile protein products encoded by globally or differentially expressed cDNA clones. Array technology was enabled by the development of devices that could array biological samples at high density with high precision onto immobilizing surfaces, ranging from the classic microtiter plate to new chip-sized supports. In addition, the introduction of automated technology to the protein level involves the simultaneous expression of a large number of cDNA clones in an appropriate vector and expression system, allowing the specific detection and purification of all the recombinant proteins. With the ordered arrangement of recombinantly expressed proteins, a direct link to the corresponding DNA sequence information is possible and consequently, clone libraries become amenable to be integrated in a database including all steps from DNA sequencing to functional assays of the translated gene product. Here, we review the generation and application of microarray technology as a highly parallel approach to obtain more information on the regulation of proteins, their biochemical function and potential interaction partners. Already, a large variety of assays based on antibody-antigen interaction exists and in addition, the medical relevance of protein arrays will be discussed. Also, further applications such as protein-DNA, protein-RNA and protein-substrate interactions will be presented, since initial studies on immobilized proteins were reported.Proteomics is an emerging field to profile protein repertoires. Because there is no reliable correlation between gene activity monitored by genomic studies and cellular protein abundance, application of protein arrays will link both genomics and proteomics.