Ribosome-inactivating proteins (RIPs) function to inhibit protein synthesis through the removal of specific
adenine residues from eukaryotic ribosomal RNA and rending the 60S subunit unable to bind elongation factor 2. They
have received much attention in biological and biomedical research due to their unique activities toward tumor cells, as
well as the important roles in plant defense. Alpha-momorcharin (α-MC), a member of the type I family of RIPs, is rich in
the seeds of Momordica charantia L. Previous studies demonstrated that α-MC is an effective antifungal and antibacterial
protein. In this study, a detailed analysis of the DNase-like activity of α-MC was conducted. Results showed that the
DNase-like activity toward plasmid DNA was time-dependent, temperature-related, and pH-stable. Moreover, a requirement
for divalent metal ions in the catalytic domain of α-MC was confirmed. Additionally, Tyr93 was found to be a critical
residue for the DNase-like activity, while Tyr134, Glu183, Arg186, and Trp215 were activity-related residues. This study on
the chemico-physical properties and mechanism of action of α-MC will improve its utilization in scientific research, as
well as its potential industrial uses. These results may also assist in the characterization and elucidation of the DNase-like
enzymatic properties of other RIPs.
Keywords: Active residue, activity-related residues, alpha-momorcharin, DNase-like activity, polynucleotide: adenosine glycosidase
activity, ribosome-inactivating proteins.
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