Lateral diffusion of human CD2 wild type and mutants with large deletions in the transmembrane domain

Integral membrane proteins anchor to the cell surface and span the lipid bilayer by an alpha-helix of 17-30 amino acids, the transmembrane segment. However, little is known about the association of this alpha-helix and the lipid bilayer. In the present study human CD2 molecule was chosen as a model for an integral membrane protein. Truncate forms with transmembrane segments 14 and 12 amino acids long were created by oligonucleotide site-directed mutagenesis. Lateral diffusion revealed that even large deletions in the membrane domain of CD2 do not interfere with its lateral mobility. On the other hand, the fraction of free molecules for diffusion was higher in CD2 protein with transmembrane region 12 amino acids long. These results suggest that deletions in the transmembrane domain can interfere with the stability of the protein within the lipid bilayer.