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Potential role for CA-SP in nucleating retroviral capsid maturation
Matthew R England1, John G Purdy1, Ira J Ropson2
1Department of Microbiology and Immunology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania, USA.
Journal of Virology
|April 11, 2014
Summary
The Rous sarcoma virus spacer peptide (SP) actively promotes mature capsid assembly. This intermediate protein fragment, CA-SP, accelerates capsid formation and acts as a nucleation site for assembly.
Area of Science:
- Virology
- Structural Biology
- Biochemistry
Background:
- The Rous sarcoma virus (RSV) capsid protein (CA) is derived from a Gag polyprotein precursor.
- During virion maturation, proteolytic cleavage releases CA-SP, an intermediate form, followed by further processing to mature CA and CA-S proteins.
- The spacer peptide (SP) is crucial for stabilizing immature Gag hexamers, but its role after cleavage is less understood.
Purpose of the Study:
- To investigate the biophysical and biochemical properties of the CA-SP intermediate.
- To determine the role of SP in promoting mature Rous sarcoma virus capsid assembly.
Main Methods:
- Biophysical characterization of CA-SP.
- Biochemical assays to assess assembly behavior.
- Cryo-electron microscopy (cryo-EM) structure analysis.
Main Results:
- Monomeric CA-SP self-assembles into capsid-like structures identical to those formed by mature CA.
- CA-SP exhibits rapid assembly kinetics, suggesting higher affinity interactions than mature capsid proteins.
- CA-SP can nucleate the assembly of CA and CA-S, with assembly order sensitive to the N-terminal β-hairpin.
Conclusions:
- The spacer peptide (SP) possesses a previously unrecognized activity in promoting mature capsid assembly.
- CA-SP acts as a potent nucleator, actively facilitating the formation of mature retroviral capsids.
- This finding has implications for understanding retroviral maturation and potential therapeutic strategies targeting the spacer peptide.
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