Solution structure of the cytoplasmic domain of the human CD4 glycoprotein by CD and 1H NMR spectroscopy: implications for biological functions.

The human T cell receptor CD4 is a type I integral membrane glycoprotein that is involved in T cell activation and also acts as the primary coreceptor for human immunodeficiency viruses (HIV). Here the structure of a synthetic 38 amino acid peptide corresponding to the complete cytoplasmic domain of CD4 (CD4CYTO) has been investigated under a variety of solution conditions using a combination of circular dichroism and homonuclear two-dimensional 1H nuclear magnetic resonance spectroscopy. In the presence of the membrane mimetic 2,2,2-trifluoroethanol (TFE), a conformational change of CD4CYTO from a random coil to an alpha-helical structure was observed.