The Tumor Cell Proliferation Inhibitory Activity of the Human Herpes Virus Type 6 U94 Protein Relies on a Stable Tridimensional Conformation

The U94 protein of Human Herpesvirus 6 exerts antiproliferative effects through downregulation of the <i>Src</i> proto-oncogene. We aimed to define the shortest U94 fragment that preserves antiproliferative activity and to explore its structural properties. U94 was truncated into shorter fragments, which were subjected to computational analyses and proliferation assays on MDA-MB-468, BT-549 breast cancer cells. Src phosphorylation levels were scrutinized by Western blot analysis. Data obtained demonstrated that the U94 antiproliferative activity resides in its N-terminal region. Specifically, MT153 (aa 1-153) and MT117 (aa 1-117) fragments exhibited antiproliferative activity, whereas MV85 (aa 1-85) fragment did not. Computational analyses identified MG112 (aa 1-112) and MI108 (aa 1-108) as biologically active and suggested that the β-sheet of the structure is critical. The shortest KI95 fragment (aa 14-108), maintaining a stable β-sheet, demonstrated antiproliferative effects and <i>Src</i> downregulation. The antiproliferative activity of U94 and its active fragments relies on stable tridimensional conformation rather than on linear peptide sequence. KI95 represents the shortest active U94 fragment that preserves biological function, with critical residues likely located within the β-sheet region. These findings highlight the importance of structural integrity in U94 functionality and suggest KI95 as a potential therapeutic agent for cancer treatment.