HIV-1 Matrix Protein Interactions with tRNA: Implications for Membrane Targeting

Area of Science:

• Virology
• Molecular Biology
• Structural Biology

Background:

• The N-terminally myristoylated matrix (MA) domain of HIV-1 Gag protein targets the virus to the plasma membrane.
• Cytoplasmic tRNAs, including tRNA^Lys3, associate with MA prior to membrane binding.
• Ternary complex formation involving MA, tRNA, and the membrane is proposed to be critical for HIV-1 assembly and membrane discrimination.

Purpose of the Study:

• To characterize the interactions between the HIV-1 MA domain and tRNA^Lys3.
• To investigate the impact of tRNA binding on MA's membrane association.
• To elucidate the role of these interactions in HIV-1 assembly.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy to study protein-tRNA interactions.
• Isothermal Titration Calorimetry (ITC) to quantify binding affinities.
• Liposome binding assays to assess membrane association.

Main Results:

• Ternary complex formation between MA and tRNA^Lys3 involves a basic residue patch also important for PI(4,5)P₂ binding.
• MA exhibits a significantly higher affinity for tRNA^Lys3 (K_d = 0.63 µM) than for PI(4,5)P₂-enriched liposomes (K_d(apparent) = 10.2 µM).
• tRNA^Lys3 binding competitively inhibits MA association with various lipid compositions, including those mimicking the plasma membrane.

Conclusions:

• tRNA^Lys3 binding to MA acts as a critical regulator, preventing premature membrane association.
• The findings support models where Gag-Gag interactions, promoting myristate exposure, modulate tRNA binding and subsequently influence membrane targeting.
• This study mechanistically links Gag genome binding (via tRNA) to membrane targeting, providing insights into HIV-1 assembly regulation.