Proximity Ligation as a Universal Protein Detection Tool

Among the great challenges in biology are the precise quantification of specific sets of proteins and analyses of their patterns of interaction on a much larger scale than is possible today. This thesis presents a novel protein detection technique - proximity ligation - and reports the development and application of a nucleic acid amplification technique, RCA. Proximity ligation converts information about the presence or co-localization of specific proteins to unique sets of nucleic acid sequences. For detection of target proteins or protein complexes the coincident binding by pairs or triplets of specific protein-binding reagents are required. Oligonucleotide-extensions attached to those binding reagents are joined by a DNA ligase and subsequently analyzed by standard molecular genetic techniques. The technique is shown to sensitively detect an assortment of proteins using different types of binders converted to proximity probes, including SELEX aptamers and mono- and polyclonal antibodies. I discuss factors important for using the technique to analyze many proteins simultaneously. Quantification of target molecules requires precise amplification and detection. I show how rolling circle amplification, RCA, can be used for precise quantification of circular templates using modified molecular beacons with real-time detection. The combination of proximity-probe templated circularization and RCA results in a sensitive method with high selectivity, capable of visualizing individual immobilized proteins. This technique is used for localized detection of a set of individual proteins and protein complexes at sub-cellular resolution