The primary cell wall of higher plants is a focal point for growth regulation and disease resistance. This wall is a cell organelle; it has structural integrity, enzymic autonomy, and self-organizing properties. This research focuses on one set of macromolecules, the extensins, which, because of their location, shape, chemistry and especially their tacticity (orderliness), may play a crucial role as organizers by virture of their ability to form highly ordered crosslinked networks that mechanically couple the cellulose load-bearing polymers. Previous work demonstrated extensin peptide periodicity and isodityrosine as a short intramolecular link; identified a putative crosslink domain; and purified a cell wall enzyme, extensin peroxidase, which specifically crosslinks extensin monomers in vitro. This project will define both the properties of extensin peroxidase and its product, the extensin network. In particular it will define substrate specificity to identify the minimum structure required for crosslinking. The work supported by this grant continues a long term effort to understand the role of one type of protein in the primary cell walls of plants. The PI has proposed a "warp-weft" model for cell wall structure based on the idea that the structural protein extension mechanically couples the load-bearing cellulosic polymers.
