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Proteolytic cleavage of microtubule-associated proteins by retroviral proteinases
Abstract:
Aspartic proteinases from human immunodeficiency virus type 1 (HIV-1) and avian myeloblastosis virus (AMV) were found to interfere with microtubule assembly. Preincubation of the proteinases with purified brain microtubule proteins (tubulin and microtubule-associated proteins) at low ionic strength (pH 6.8), completely inhibited microtubule assembly. Analysis of microtubule proteins after incubation with proteinase showed no effect on tubulin but extensive cleavage of the microtubule-associated proteins 1 and 2 was observed. The digestion by the two proteinases differed. In the presence of HIV-1 proteinase, a fragment with an Mr of approximately 300, appeared, as well as at least three other new fragments, with Mr values of 188,000, 124,000 and 73,000. In the presence of AMV proteinase, the microtubule-associated proteins were extensively digested to many small fragments. The extending microtubule-associated proteins normally seen by electron microscopy on the microtubule surface disappeared after treatment with AMV proteinase. Our results show that retroviral proteinases are not restricted to cleavage of viral polyproteins in vitro. It is suggested that proteolysis of microtubular proteins by viral proteinases is an important step in viral pathogenicity and that it may be part of a mechanism causing degenerative effects in infected cells.
Insights
Retroviral aspartic proteinases from HIV-1 and AMV disrupt microtubule assembly by cleaving microtubule-associated proteins. This proteolysis may contribute to viral pathogenicity and cellular degeneration.
Area of Science:
- Molecular Biology
- Virology
- Cell Biology
Background:
- Microtubules are essential cytoskeletal components involved in cell structure and division.
- Retroviral aspartic proteinases are crucial for viral replication, typically cleaving viral polyproteins.
Purpose of the Study:
- To investigate the effect of human immunodeficiency virus type 1 (HIV-1) and avian myeloblastosis virus (AMV) aspartic proteinases on microtubule assembly.
- To determine if these viral proteinases can cleave microtubule-associated proteins (MAPs).
Main Methods:
- Purified brain microtubule proteins (tubulin and MAPs) were incubated with HIV-1 and AMV proteinases at low ionic strength.
- Microtubule assembly was assessed, and protein digestion patterns were analyzed using molecular weight estimations and electron microscopy.
Main Results:
- Both HIV-1 and AMV proteinases completely inhibited microtubule assembly.
- Tubulin integrity was maintained, but microtubule-associated proteins 1 and 2 were extensively cleaved.
- HIV-1 proteinase produced specific fragments, while AMV proteinase yielded numerous small fragments, causing the disappearance of surface-extending MAPs.
Conclusions:
- Retroviral aspartic proteinases possess broader substrate specificity than previously known, extending to host cellular proteins like MAPs.
- Proteolysis of microtubular proteins by viral proteinases is proposed as a mechanism contributing to viral pathogenicity and cellular degenerative effects.