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Published on: March 22, 2016
Properties of a P70 proteolytic factor of murine leukemia viruses
Abstract:
Murine leukemia viruses, such as Rauscher leukemia virus (RLV), contain a proteolytic factor which becomes activated after detergent treatment of the virus. This factor specifically cleaves P70, the gag precursor polyprotein which is enriched for in preparations of immature virus core subparticles. The factor has been partially purified on Sephadex G-75 columns. It has a molecular weight of 10,000-12,000 daltons but does not coincide in elution position with the major peaks of the viral polypeptides p10 or p12. Under optimal conditions, that is 2% NP-40 (v/v), 10 mM DTT, (pH 7.2) and incubation for 16 hr at 22 degrees C, cleavage of labeled P70 occurs and increasing amounts of the four gag polypeptides p30, p15, p12 and p10 are obtained. The P70 cleavage activity is blocked by TLCK, TAME, CBZ-lysine and other lysyl-containing protease inhibitors. Further, the CBZ-lysine inhibition is reversible, while an inhibition by phenyl-methylsulfonyl fluoride (PMSF) is irreversible. These inhibition studies suggest that a similarity exists between the P70 proteolytic factor and some serine proteases, such as trypsin. The cleavage pattern of P70-rich immature cores treated with trypsin or chymotrypsin is different from that obtained with the P70 proteolytic factor. Thus murine leukemia virions apparently contain a unique, highly specific protease which is present in small amounts and cleaves P70.
Insights
Murine leukemia viruses possess a unique protease that cleaves the P70 gag precursor protein into smaller viral polypeptides. This specific protease activity is essential for viral maturation and is inhibited by certain protease inhibitors.
Area of Science:
- Virology
- Molecular Biology
- Proteomics
Background:
- Murine leukemia viruses (MLVs), like Rauscher leukemia virus (RLV), are retroviruses known to cause leukemia in mice.
- Viral maturation involves the proteolytic processing of precursor polyproteins into functional viral proteins.
Purpose of the Study:
- To characterize the proteolytic factor responsible for cleaving the P70 gag precursor polyprotein in MLVs.
- To investigate the properties and specificity of this viral protease.
Main Methods:
- Partial purification of the proteolytic factor using Sephadex G-75 chromatography.
- Analysis of P70 cleavage products under optimized conditions (detergent, DTT, pH, temperature, time).
- Inhibition studies using various protease inhibitors (TLCK, TAME, CBZ-lysine, PMSF) and comparison with trypsin/chymotrypsin cleavage.
Main Results:
- A unique proteolytic factor, with a molecular weight of 10,000-12,000 daltons, was identified in MLVs.
- This factor specifically cleaves the P70 gag precursor into p30, p15, p12, and p10 polypeptides.
- Inhibition studies suggest the protease shares characteristics with serine proteases, but exhibits unique cleavage specificity compared to trypsin or chymotrypsin.
Conclusions:
- MLVs contain a specific, low-abundance protease essential for P70 processing.
- The protease's unique characteristics differentiate it from host or other viral proteases.
- Understanding this protease could offer insights into MLV replication and pathogenesis.
