Wheat ribosome-inactivating proteins: seed and leaf forms with different specificities and cofactor requirements

Area of Science:

• Plant Biochemistry
• Molecular Biology
• Protein Chemistry

Background:

• Ribosome-inactivating proteins (RIPs) are enzymes that inhibit protein synthesis.
• Wheat (Triticum aestivum L.) contains various RIPs with distinct properties.
• Understanding RIPs is crucial for their potential applications in biotechnology and medicine.

Purpose of the Study:

• To purify and characterize two distinct RIPs from wheat germ and leaves.
• To investigate the differences in substrate specificity and cofactor requirements between these two proteins.
• To compare their enzymatic activity on ribosomes from various sources.

Main Methods:

• Purification of tritin-S from wheat germ and tritin-L from wheat leaves.
• Characterization of protein size, charge, and antigenic properties.
• Assay of RNA N-glycosidase activity on ribosomes from yeast, wheat, tobacco, E. coli, and rabbit reticulocytes.
• Investigation of cofactor requirements, including ATP.

Main Results:

• Tritin-S and tritin-L were purified and found to be antigenically unrelated, differing in size and charge.
• Both proteins act as RNA N-glycosidases, cleaving A3024 in 26S rRNA of yeast ribosomes.
• Tritin-S and tritin-L display distinct substrate specificities and cofactor requirements.
• Tritin-S requires ATP for activity, while tritin-L does not show this requirement.
• Tritin-L exhibits broader activity across different ribosome sources compared to tritin-S.

Conclusions:

• Wheat germ and leaves synthesize distinct ribosome-inactivating proteins with unique biochemical properties.
• The differential substrate specificity and cofactor dependency suggest specialized roles for tritin-S and tritin-L.
• These findings contribute to the understanding of RIP diversity and function in plants.