Isolation and analysis of fungal phosphorylated proteoglycan

Abstract

A low molecular-weight phosphorylated proteoglycan (PPG) was isolated from the freshwater fungus Achlya by cold osmotic-shock treatment of newly germinated spores and purified. PPG contained 38.5% carbohydrate (89% glucose), 33% protein, and 28.5% phosphate. There was the equivalent of one uracil base in the form of uridylate per PPG molecule. The molecular weight estimations by Sephadex G-50 bead filtration, electrophoresis, and chemical analysis were in agreement. The values varied from 6000–7000. Most of the amino acids (21 residues) were D-optical isomers. All of the glucose molecules were in phosphodiester linkage as acid hydrolysis of PPG yielded mainly glucose-6-phosphate, some free glucose, and Pi. PPG, therefore, may be a sugar–phosphate polymer with peptides attached at one or more sites. The uracil moiety is covalently attached to the PPG probably as UDPG.Loosely associated with the PPG were three polyphosphorylated dinucleosides, HS3, HS2, and HS1, which were easily displaced when the PPG was filtered through a Sephadex G-50 column. Neither Mg(II) nor Ca(II) could stabilize the association. Hg(II), Ag(I), and KI altered the uv-absorption spectra of HS compounds and HS-free PPG in an identical manner. This was attributed to the uracil derivative present in all HS compounds and PPG. Similar changes were shown with authentic UDPG, UDP, and UMP, not uridine, when they complexed with Hg(II), Ag(I),and KI.Both PPG and(or) HS compounds may play an essential role in cell growth as their removal by osmotic shock arrested further development until they were relaid in the cell wall membrane complex. We suggest that PPG may have a function(s) similar to those assigned to teichoic acids and sugar–phosphate polymers of bacteria.