Evidence that the translocon may function as a hydropathy partitioning filter.
Developing a greater understanding of the function of the translocon-and the source of its selectivity for transmembrane helix insertion-are important steps toward deciphering the role of disease-causing mutations in membrane regions. To address these phenomena, we have prepared a library of helix-loop-helix ("hairpin") constructs derived from helices 3 and 4 of the first membrane domain of CFTR, in which position 232 was mutated individually to each of the 20 commonly-occurring amino acids. Using retention times on a reverse phase-HPLC C18 column to mimic the process of hairpin partitioning, we have quantitatively determined a hydropathy scale in the context of a bona fide membrane protein fragment that correlates to an in vivo hydropathy scale with r=-0.78-a value that rises to r=-0.92 when Asp and Glu are excluded due to protonation effects. Our results provide evidence that the translocon may act as a facilitator in the insertion selection process, effectively allowing the bilayer to "decide" through favorable non-polar solvation whether or not to allow a translocating helix to enter the membrane.
Mulvihill
Cory M
CM
Division of Molecular Structure and Function, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8.
Deber
Charles M
CM
D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008051:Lipid Bilayers / Q000737:chemistry; D008565:Membrane Proteins / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed / Q000379:methods; D009154:Mutation; D010455:Peptides / Q000737:chemistry* / Q000235:genetics; D017510:Protein Folding; D017433:Protein Structure, Secondary
D008051:Lipid Bilayers; D008565:Membrane Proteins; D010455:Peptides; D019005:Cystic Fibrosis Transmembrane Conductance Regulator