Ranpirnase is a ribonuclease enzyme found in the oocytes of the Northern Leopard Frog (Rana pipiens). Ranpirnase is a member of the pancreatic ribonuclease (RNase A) protein superfamily and degrades RNA substrates with a sequence preference for uracil and guanine nucleotides. Along with amphinase, another leopard frog ribonuclease, Ranpirnase has been studied as a potential cancer and antiviral treatment due to its unusual mechanism of cytotoxicity tested against transformed cells and antiviral activity.
Ranpirnase was originally discovered by scientists at TamirBio, a biotechnology company (formerly Alfacell Corporation), where it was tested in preclinical assays and in clinical trials under the name Pannon or Onconase, and TMR004. The mechanism of action of ranpirnase has been attributed to the RNA interference pathway, potentially through cleaving siRNA molecules; to cleavage of transfer RNA; Currently (as of March 2020) Ranpirnase is in clinical trials as a potential antiviral.
EC number
The EC system, or enzyme classification system was created to both standardize enzyme names, as well as allow for association of enzyme reaction type and function. The EC number for Ranpirnase is EC 4.6.1.18, but was previously EC 3.1.27.5. This means that ranpirnase is in class 4, subclass 6, sub-subclass 1, and serial #18. Class 4 are considered lyases, while subclass 4.6.1 further classifies the enzyme as a phosphorus-oxygen lyase. Ultimately, ranpirnase can be classified as a pancreatic ribonuclease.
Structure
Ranpirnase is found in the oocytes of Rana pipiens, also known as the Northern leopard frog. These oocytes have two similar variations of pancreatic ribonuclease A, which both exhibit cytostatic and cytotoxic properties. Ranpirnase contains 104 amino acid residues, making it the smallest identified member of the RNase A superfamily. Overall, ranpirnase is considered small single chain protein that has a molecular weight around 12,000 Da. Once ranpirnase was isolated from the oocytes, it was discovered that ranpirnase is polymorphic at amino acid position 25. Specifically, this position has historically been occupied by Thr amino acids, but Ser amino acids have also been identified. This replacement, however, does not appear to change the function of the enzyme. Additionally, ranpirnase contains 4 disulfide bonds that give the enzyme high heat stability.
Structure tied to function
The structure of ranpirnase does appear to have an impact on its function. Specifically, studies suggest that ranpirnase uses Coulombic interactions as well as a hydrogen bonding system to adjust substrate specificity. Additionally, it has been seen that intentional changes in amino acid replacements can also modify substrate specificity. Studies have also investigated the structural characteristics that underlie the reduced catalytic activity of ranpirnase. This decreased catalytic activity is associated with low affinity for substrate. A solution to this appears to be undergoing T5R substitution. A T5R substitution is engineered to establish a successful Coulombic interaction between ranpirnase and a phosphoryl group in RNA. This then resulted in a twofold enhancement of ribonucleolytic activity.