The common concept in this thesis was to adapt and develop quantitative mass spectrometric assays focusing on reagents originating from the Human Protein Atlas project to quantify proteins in human cell lines, tissues and blood. The work is based around stable isotope labeled protein fragment standards that each represent a small part of a human protein-coding gene. This thesis shows how they can be used in various formats to describe the protein landscape and be used to standardize mass spectrometry experiments. The first part of the thesis describes the use of antibodies in combination with heavy stable isotope labeled antigens to establish a semi-automated protocol for protein quantification of complex samples with fast analysis time  (Paper~I). Paper II introduces a semi-automated cloning protocol that can be used to selectively clone variants of recombinant proteins, and highlights the automation process that is necessary for large-scale proteomics endeavors. This paper also describes the technology that was used to clone all protein standards that are used in all of the included papers.                       The second part of the thesis includes papers that focus on the generation and application of antibody-free targeted mass spectrometry methods. Here, absolute protein copy numbers were determined across human cell lines and tissues (Paper III) and the protein data was correlated against transcriptomics data. Proteins were quantified to validate antibodies in a novel method that evaluates antibodies based on differential protein expression across multiple cell lines (Paper IV). Finally, a large-scale study was performed to generate targeted proteomics assays (Paper V) based on protein fragments. Here, assay coordinates were mapped for more than 10,000 human protein-coding genes and a subset of peptides was thereafter used to determine absolute protein levels of 49 proteins in human serum.                       In conclusion, this thesis describes the development of methods for protein quantification by targeted mass spectrometry and the use of recombinant protein fragment standards as the common denominator. / <p>QC 20161013</p>

In the field of proteomics, proteins are analyzed and quantified in high numbers. Protein analysis is of great importance and can for example generate information regarding protein function and involvement in disease. Different strategies for protein analysis and quan- tification have emerged, suitable for different applications. The focus of this thesis lies on protein identification and quantification using different setups and method development has a central role in all included papers. The presented research can be divided into three parts. Part one describes the develop- ment of two different screening methods for His6-tagged recombinant protein fragments. In the first investigation, proteins were purified using immobilized metal ion affinity chro- matography in a 96-well plate format and in the second investigation this was downscaled to nanoliter-scale using the miniaturized sample preparation platform, integrated selective enrichment target (ISET). The aim of these investigations was to develop methods that could work as an initial screening step in high-throughput protein production projects, such as the Human Protein Atlas (HPA) project, for more efficient protein production and purification. In the second part of the thesis, focus lies on quantitative proteomics. Protein fragments were produced with incorporated heavy isotope-labeled amino acids and used as internal standards in absolute protein quantification mass spectrometry experiments. The aim of this investigation was to compare the protein levels obtained using quanti- tative mass spectrometry to mRNA levels obtained by RNA sequencing. Expression of 32 different proteins was studied in six different cell lines and a clear correlation between protein and mRNA levels was observed when analyzing genes on an individual level. The third part of the thesis involves the antibodies generated within the HPA project. In the first investigation a method for validation of antibodies using protein immunoenrichment coupled to mass spectrometry was described. In a second study, a method was developed where antibodies were used to capture tryptic peptides from a digested cell lysate with spiked in heavy isotope-labeled protein fragments, enabling quantification of 20 proteins in a multiplex format. Taken together, the presented research has expanded the pro- teomics toolbox in terms of available methods for protein analysis and quantification in a high-throughput format. / <p>QC 20141022</p>