Structural Cell Wall Proteins.

Abstract

Biological structures as diverse as skin, hair, spider webs, silk cocoons, connective tissue, and some alga1 cell walls share a common property: they consist mainly of structural proteins. Some of these proteins have been studied in detail and have contributed greatly to our understanding of protein structure. Silk fibroin, for example, is the model protein for the 0-pleated sheet secondary structure, collagen for a triplestranded helix. The amino acids Gly and Pro (or Hyp) are frequently found to be major constituents of these structural proteins and, therefore, appear to be well suited as building blocks for structural proteins. Not surprisingly, plant cell walls, the major structural part of the plant cell, also contain structural proteins. The primary amino acid sequences of many of these proteins have been deduced from cDNA and genomic sequences, but less is known about the precise localization and developmental expression pattern of these proteins. However, it has become clear that both the synthesis and the cross-linking of these wall proteins are under strict developmental control. In addition, their synthesis and cross-linking can be environmentally induced by a number of triggers. Despite our growing knowledge about these proteins, their biological function is still largely a matter of speculation. Three major classes of structural wall proteins have been recognized to date: extensins, PRPs, and GRPs. Other wall proteins that have been described might also have a structural role, but less is known about these proteins and this discussion will focus on the well-characterized wall proteins. HRGPs OR EXTENSINS