Three active forms of aspartic proteinase from Mason-Pfizer monkey virus

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• Mason-Pfizer monkey virus (M-PMV) proteinase is crucial for viral maturation, processing Gag-Pro and Gag-Pro-Pol precursors.
• Typically, retroviruses possess a single active proteinase form.

Purpose of the Study:

• To investigate the unusual existence of multiple active forms of M-PMV proteinase.
• To characterize the processing and activity of these M-PMV proteinase forms.

Main Methods:

• Mass spectrometry was used to determine the molecular masses of M-PMV proteinase forms.
• In vitro self-processing of a 26-kDa precursor was analyzed.
• Isolation and characterization of truncated proteinase products.
• Amino acid and sequence analyses (N- and C-terminal) were performed.
• Western blot or similar techniques to detect proteinase forms in virions.

Main Results:

• Three active M-PMV proteinase forms (17, 13, and 12 kDa) were identified via mass spectrometry.
• These forms result from the in vitro self-processing of a 26-kDa precursor.
• All three isolated forms demonstrated proteolytic activity.
• N-terminal sequences were identical, indicating C-terminal truncation.
• The 17-kDa and 13-kDa forms were detected in M-PMV virions from infected cells, confirming in vivo existence.

Conclusions:

• M-PMV proteinase exists in multiple active forms (17, 13, and 12 kDa), unlike most retroviruses.
• Autoprocessing occurs at the C-terminus of the 17-kDa form to generate smaller active species.
• These multiple proteinase forms are biologically relevant, existing both in vitro and in vivo.