Complex sentence: Two main functions have been assigned to the Vpu protein, the first one is known to induce degradation of the viral receptor molecule CD4 and to enhance the release of newly formed virions from the cell surface.
Split into simpler sentences: Two main functions have been assigned to the Vpu protein. The first function is known to induce degradation of the viral receptor molecule CD4, and the second function is to enhance the release of newly formed virions from the cell surface.