Protein phosphorylation is a major regulator of protein function and biological outcomes. This was first recognized through functional biochemical experiments, and in the past decade, major technological advances in mass spectrometry have enabled the study of protein phosphorylation on a global scale. This rapidly growing field of phosphoproteomics has revealed that more than 100,000 distinct phosphorylation events occur in human cells, which likely affect the function of every protein. Phosphoproteomics has improved the understanding of the function of even the most well-characterized protein kinases by revealing new downstream substrates and biology. However, current biochemical and bioinformatic approaches have only identified kinases for less than 5% of the phosphoproteome, and functional assignments of phosphosites are almost negligible. Notably, our understanding of the relationship between kinases and their substrates follows a power law distribution, with almost 90% of phosphorylation sites currently assigned to the top 20% of kinases. In addition, more than 150 kinases do not have a single known substrate. Despite a small group of kinases dominating biomedical research, the number of substrates assigned to a kinase does not correlate with disease relevance as determined by pathogenic human mutation prevalence and mouse model phenotypes. Improving our understanding of the substrates targeted by all kinases and functionally annotating the phosphoproteome will be broadly beneficial. Advances in phosphoproteomics technologies, combined with functional screening approaches, should make it feasible to illuminate the connectivity and functionality of the entire phosphoproteome, providing enormous opportunities for discovering new biology, therapeutic targets, and possibly diagnostics.

蛋白质磷酸化是蛋白质功能和生物学结果的主要调节剂。这首先通过功能性生化实验得到认可，并且在过去的十年中，质谱技术的重大技术进步已使蛋白质磷酸化的研究得以在全球范围内进行。迅速发展的磷酸化蛋白质组学领域表明，在人类细胞中发生了超过100,000个不同的磷酸化事件，这很可能会影响每种蛋白质的功能。磷酸蛋白质组学通过揭示新的下游底物和生物学特性，甚至提高了对最典型的蛋白激酶功能的理解。然而，当前的生物化学和生物信息学方法仅鉴定了少于5％的磷酸化蛋白质组的激酶，并且磷酸位点的功能分配几乎可以忽略不计。值得注意的是，我们对激酶及其底物之间关系的理解遵循幂律分布，目前将近90％的磷酸化位点分配给了激酶的前20％。另外，超过150种激酶没有单一已知的底物。尽管一小部分激酶在生物医学研究中占主导地位，但分配给该激酶的底物数量与致病性人类突变发生率和小鼠模型表型所确定的疾病相关性并不相关。增进我们对所有激酶靶向的底物的了解并在功能上注释磷酸化蛋白质组将是广泛有益的。磷酸化蛋白质组学技术的进步与功能筛选方法的结合，应该使阐明整个磷酸化蛋白质组学的连通性和功能性变得可行，