15N-metabolic labeling for comparative plasma membrane proteomics in Arabidopsis cells.

An important goal for proteomic studies is the global comparison of proteomes from different genotypes, tissues, or physiological conditions. This has so far been mostly achieved by densitometric comparison of spot intensities after protein separation by 2-DE. However, the physicochemical properties of membrane proteins preclude the use of 2-DE. Here, we describe the use of in vivo labeling by the stable isotope 15 N as an alternative approach for comparative membrane proteomic studies in plant cells. We confirm that 15 N.metabolic labeling of proteins is possible and efficient in Arabidopsis suspension cells. Quantification of 14 N versus 15 N MS signals reflects the relative abundance of 14 N and 15 N proteins in the sample analyzed. We describe the use of 15 N-metabolic labeling to perform a partial comparative analysis of Arabidopsis cells following cadmium exposure. By focusing our attention on plasma membrane proteins, we were able to confidently identify proteins showing up to 5-fold regulation compared to unexposed cells. This study provides a proof of principle that 15 N-metabolic labeling is a useful technique for comparative membrane proteome studies.