A cytotoxic type-2 ribosome inactivating protein (from leafless mistletoe) lacking sugar binding activity

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• Ribosome inactivating proteins (RIPs) are cytotoxic enzymes often found in plants.
• The toxicity of RIPs is typically linked to the presence and sugar-binding activity of their B-chain.
• Mistletoe lectins are a well-studied class of RIPs.

Purpose of the Study:

• To characterize a novel RIP, Articulatin-D, purified from Viscum articulatum.
• To investigate the functional properties of Articulatin-D's A- and B-chains.
• To determine the relationship between the B-chain's sugar-binding activity and the protein's cytotoxicity.

Main Methods:

• Purification of Articulatin-D from Viscum articulatum.
• N-terminal sequencing and LC-MS/MS analysis of A- and B-chains.
• Assays for translation inhibition, N-glycosidase activity, and sugar-binding.
• Cytotoxicity assays (IC50) against various human cancer cell lines.

Main Results:

• Articulatin-D is a type-2 RIP with a catalytically active A-chain.
• The B-chain of Articulatin-D lacks detectable sugar-binding activity and hemagglutination properties.
• Articulatin-D demonstrates significant cytotoxicity against multiple cancer cell lines with low IC50 values.

Conclusions:

• Articulatin-D is the first identified cytotoxic RIP with a non-sugar-binding B-chain.
• This discovery necessitates a re-evaluation of the role of B-chain sugar-binding activity in RIP-mediated cytotoxicity.
• Articulatin-D presents a new avenue for understanding and potentially developing RIP-based therapeutics.