Conformational Lability of Herpesvirus Protein VP22*

The herpesvirus protein VP22 traffics between cells, being exported from expressing cells in a non-Golgi-dependent manner and localizing in the nuclei of surrounding cells. This transport is retained in certain VP22 fusion proteins, making VP22 a candidate for use in macromolecular drug delivery. In an effort to understand the physical basis for this activity, we have initiated structural studies of VP22.C1, the C-terminal half of VP22, which possesses the full transport activity of the native protein. CD and Fourier transform infrared analyses indicate a secondary structure consisting of approximately 30% α-helix, 17% β-sheet, and 51% disordered and turn structure. Unfolding studies conducted by CD, differential scanning calorimetry, and fluorescence reveal a series of discrete structural transitions in the range of 20–60 °C. CD and fluorescence studies of interactions between VP22.C1 and divalent cations and model polyanions indicate that Mg2+, Zn2+, oligonucleotides, and heparin interact with the protein, causing changes in secondary structure and thermal stability. Additionally, the interaction of VP22.C1 with model lipids was examined. Fluorescence titrations of the protein withtrans-parinaric acid at various temperatures suggest the binding of one to two molecules of parinaric acid to VP22.C1 at temperatures >40 °C, suggesting the possibility of conformation dependent membrane interaction under physiological conditions.

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