DIFFERENTIAL EXTRACTION AND PROTEIN SEQUENCING REVEALS MAJOR DIFFERENCES IN PATTERNS OF PRIMARY-CELL WALL PROTEINS FROM PLANTS

The proteins of the primary cell walls of suspension cultured cells of five plant species, Arabidopsis, carrot, French bean, tomato, and tob acco, have been compared, The approach that has been adopted is differ ential extraction followed by SDS-polyacrylamide gel electrophoresis ( PAGE), rather than two-dimensional gel analysis, to facilitate protein sequencing, Whole cells were washed sequentially with the following a queous solutions, CaCl2, CDTA (cyclohexane diaminotetraacetic acid, DT T (dithiothreitol), NaCl, and berate, SDS-PAGE analysis showed consist ent differences between species, From the 233 proteins that were selec ted for sequencing, 63% gave N-terminal data. This analysis shows that (i) patterns of proteins revealed by SDS-PAGE are strikingly differen t for all five species, (ii) a large number of these proteins cannot b e identified by data base searches indicating that a significant propo rtion of wall proteins have not been previously described, (iii) the m ajor proteins that can be identified belong to very different classes of proteins, (iv) the majority of proteins found in the extracellular growth media are absent from their respective cell wall extracts, and (v) the results of the extraction process are indicative of higher ord er structure, It appears that aspects of speciation reside in the comp lement of extracellular wall proteins, The data represent a protein re source for cell wall studies complementary to EST (expressed sequence tag) and DNA sequencing strategies.