CONSERVED AMINO-ACID-RESIDUES IN RIBOSOME-INACTIVATING PROTEINS FROM PLANTS

The amino acid sequences of eleven RIPs sequenced to date have been compared in the expectation that this would be useful in the location of functionally and/or structurally important sites of these molecules. In addition to several highly conserved hydrophobic amino acids, thirteen absolutely conserved residues have been found in ricin A-chain: Tyr21, Phe24, Arg29, Tyr80, Tyr123, Gly140, Ala165, Glu177, Ala178, Arg180, Glu208, Asn209 and Trp211. The role of these residues as well as of the C-terminal region have been discussed based on the results of chemical and enzymatic modifications, site-directed mutagenesis, and deletion studies.