Crystalline glycoprotein cell walls of algae: their stucture, composition and assembly

Abstract

Cell walls from various algae within the Chlamydomonaceae display, when negatively stained and examined in the electron microscope, a crystalline lattice component. On the basis of the Fourier transforms of micrographs of the cell wall, the algae have been classified into five classes. Most of the algae examined fall into class II. The two-dimensional repeating morphological unit cell of the wall of each class is described and in each case is a parallelogram whose overall dimensions are all of the same order of magnitude. The implications of the classification for classical taxonomy are discussed. More detailed structural information, to a resolution of about 2.5 nm (based on optical filtering and image enhancement techniques), is presented for two of the cell wall classes. From the evidence of polyacrylamide gel electrophoresis, the cell wall of these algae is constructed primarily from a small number of high molecular mass glycoprotein species. In Chlamydomonas reinhardi it has been shown that the hydroxyproline residues in the wall glycoprotein are cross-linked to short oligosaccharides. Some of the conditions necessary for the complete in vitro reassembly of the cell wall of C. reinhardi are presented and include the presence of a discrete nucleating agent and the presence of a physical surface. Dislocations within the crystalline lattice of the cell walls are described and their role as growth points discussed.