Zinc-binding site of human immunodeficiency virus 2 Vpx prevents instability and dysfunction of the protein

Human immunodeficiency virus 2 Vpx coordinates zinc through residues H39, H82, C87 and C89. We reported previously that H39, H82 and C87 mutants maintain Vpx activity to facilitate the degradation of SAMHD1. Herein, the expression of Vpx mutants in cells was examined in detail. We demonstrated that the zinc-binding site stabilizes the protein to keep its function in virus growth when low levels of Vpx are expressed. At higher levels of expression, Vpx aggregation could occur, and zinc binding would suppress such aggregation. Among the amino acids involved in zinc coordination, H39 plays the most critical role. In summary, zinc binding appears to mitigate flexibility of the three-helix fold of Vpx, thereby preventing dysfunction.