A ribosomal protein is specifically recognized by saporin, a plant toxin which inhibits protein synthesis.
Many plants express enzymes which specifically remove an adenine residue from the skeleton of the 28 S RNA in the major subunit of the eukaryotic ribosome (ribosome inactivating proteins, RIPs). The site of action of RIPs (A4324 in the rRNA from rat liver) is in a loop structure whose nucleotide sequence all around the target adenine is also conserved in those species which are completely or partially insensitive to RIPs. In this paper we identify a covalent complex between saporin (the RIP extracted from Saponaria officinalis) and ribosomal proteins from yeast (Saccharomyces cerevisiae), by means of chemical crosslinking and immunological or avidin-biotin detection. The main complex (mol. wt. congruent to 60 kDa) is formed only with a protein from the 60 S subunit of yeast ribosomes, and is not detected with ribosomes from E. coli, a resistant species. This observation supports the hypothesis for a molecular recognition mechanism involving one or more ribosomal proteins, which could provide a 'receptor' site for the toxin and favour optimal binding of the target adenine A4324 to the active site of the RIP.
Ippoliti
R
R
Department of Biochemical Sciences, University of Rome La Sapienza, Italy.
Lendaro
E
E
Bellelli
A
A
Brunori
M
M
D000972:Antineoplastic Agents, Phytogenic / Q000378:metabolism*; D015153:Blotting, Western; D005656:Fungal Proteins / Q000378:metabolism*; D000922:Immunotoxins; D009699:N-Glycosyl Hydrolases; D010940:Plant Proteins / Q000378:metabolism*; D012269:Ribosomal Proteins / Q000378:metabolism*; D054789:Ribosome Inactivating Proteins, Type 1; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D000076985:Saporins
D000972:Antineoplastic Agents, Phytogenic; D005656:Fungal Proteins; D000922:Immunotoxins; D010940:Plant Proteins; D012269:Ribosomal Proteins; D054789:Ribosome Inactivating Proteins, Type 1; D009699:N-Glycosyl Hydrolases; D000076985:Saporins