Features of the SIVmac transmembrane glycoprotein cytoplasmic domain that are important for Env functions

Area of Science:

• Virology
• Molecular Biology
• Immunology

Background:

• The cytoplasmic domain (CD) of the Simian Immunodeficiency Virus macaque (SIVmac) transmembrane protein (TM) influences viral infectivity.
• Truncated CDs are disadvantageous in vivo and in vitro, suggesting their importance for viral persistence.

Purpose of the Study:

• To investigate the role of specific features within the SIVmac TM CD, including its C-terminal alpha helix and overall length.
• To elucidate how mutations in the TM CD affect viral infectivity, envelope stability, fusogenic capacity, and virion incorporation.

Main Methods:

• Site-directed mutagenesis was employed to create SIVmac TM mutants with altered cytoplasmic domains.
• Infectivity assays were performed in lymphoid cell lines.
• Detailed analyses were conducted to assess envelope stability, fusogenic capacity, and virion incorporation of mutant viruses.

Main Results:

• Mutations in the SIVmac TM CD significantly reduced or delayed virus infectivity.
• A 64-residue CD mutant exhibited rapid degradation, indicating instability.
• A mutant lacking the C-terminal alpha helix showed high fusogenicity but poor virion incorporation.
• Modifications to the C-terminal helix charge density resulted in enhanced fusogenicity and cytopathic effects but delayed replication.

Conclusions:

• Sequence variations in the SIVmac TM CD lead to functional tradeoffs, optimizing some Env functions at the expense of others.
• The CD's length, C-terminal helix, and charge density are critical for maintaining viral infectivity and persistence.