Hydropathy Analysis of a Membrane Protein's Amino Acid Sequence Predicts

Essay

Hydropathy analysis of a membrane protein's amino acid sequence predicts the protein's transmembrane segments and orientation in the membrane.It is necessary to confirm those predictions with experimental analysis.One experimental approach for plasma membrane proteins is to use the protease trypsin to digest extracellular domains of these proteins.(Trypsin is hydrophilic and cannot cross the plasma membrane to enter the cell.)When added to cells,trypsin digests the hydrophilic portions of plasma membrane proteins exposed outside the cell into small fragments but will not have access to transmembrane or cytosolic regions of proteins.Design a general experiment using trypsin and SDS-PAGE to address membrane protein association and orientation,and describe specific expected results that would be consistent with the following predicted membrane protein associations and orientations:
a.a singlepass integral membrane protein with only its N-terminus exposed on the extracellular surface
b.a singlepass integral membrane protein with only its C-terminus exposed on the extracellular surface
c.a multipass integral membrane protein with only three hydrophilic loops exposed on the extracellular surface
d.a fatty acylated protein
e.a GPI-anchored protein