Fosfopeptiden

Fosfopeptiden are peptides that contain one or more phosphate groups covalently attached to amino acid residues. In most eukaryotic proteins, the phosphate is attached to the hydroxyl group of serine, threonine or tyrosine, forming phosphoester bonds. Phosphorylation is a reversible modification that can alter the charge, conformation, and interaction properties of a peptide or protein.

The addition and removal of phosphate groups are carried out by enzymes known as kinases and phosphatases, respectively. This regulation is central to cellular signaling, metabolism, and the control of the cell cycle. Phosphorylation can modulate enzyme activity, create docking sites for other proteins, alter subcellular localization, or affect protein stability. The phosphorylation state of a peptide is often dynamic and context-dependent, varying with cellular conditions and external stimuli.

Phosphopeptides are usually part of larger proteins and are typically analyzed through proteomics. Detecting and identifying phosphopeptides by mass spectrometry requires enrichment because phosphorylated peptides are often low in abundance. Common enrichment methods include metal oxide affinity chromatography (such as TiO2) and immobilized metal affinity chromatography (IMAC) using iron or other metals. Phosphorylation can influence MS fragmentation patterns, and neutral losses of the phosphate group are a consideration during data interpretation. Phosphopeptide analysis facilitates the mapping of signaling networks, identification of kinase substrates, and understanding disease-related changes in phosphorylation.

Applications include basic research in cell biology and clinical studies aiming to discover biomarkers. Challenges involve the lability of the phosphate group under certain conditions and the complexity of phosphosite occupancy in heterogeneous samples.