Phosphoproteomics in Plants

Abstract

Phosphorylation is, of course, one of the most prevalent mechanisms for regulation of protein function. Thus, to help advance understanding of such regulation in plants, Nuhse et al. developed proteomic methods to identify sites of phosphorylation in membrane proteins. Large membrane-bound proteins are difficult to work with, but the authors got around this by proteolytic digestion of proteins in plasma membranes prepared from cultured Arabidopsis thaliana cells. Phosphopeptides were collected by immobilized metal-ion-affinity chromatography and identified by liquid chromatography coupled to tandem mass spectrometry. More than 300 phosphorylation sites were identified, the great majority of which were not previously described. Plants express hundreds of receptor-like Ser-Thr kinases, and it is not clear how these similar kinases produce specific signals. One clue is that about 50 phosphoproteins were identified among this family of proteins. Many modified residues were located in unconserved linker regions between the conserved kinase subdomains, which provides a new focus for studies of the regulatory roles of such modifications. The results also begin to define characteristics of phosphorylation sites in plants, which appear not to be well predicted with algorithms based on mammalian phosphoprotein. The data are made available on the Web in a searchable database. T. S. Nühse, A. Stensballe, O. N. Jensen, S. C. Peck, Phosphoproteomics of the Arabidopsis plasma membrane and a new phosphorylation site database. Plant Cell 16 , 2394-2405 (2004). [Abstract] [Full Text]