Formation of cytoplasmic turns between two closely spaced transmembrane helices during membrane protein integration into the ER membrane.
The helical hairpin, two closely spaced transmembrane helices separated by a short turn, is a recurring structural element in integral membrane proteins, and may serve as a compact unit that inserts into the membrane en bloc. Previously, we have determined the propensities of the 20 natural amino acids, when present in the middle of a long hydrophobic stretch, to induce the formation of a helical hairpin with a lumenally exposed turn during membrane protein assembly into the endoplasmic reticulum membrane. Here, we present results from a similar set of measurements, but with the turn placed on the cytoplasmic side of the membrane. We find that a significantly higher number of turn-promoting residues need to be present to induce a cytoplasmic turn compared to a lumenal turn, and that, in contrast to the lumenal turn, the positively charged residues Arg and Lys are the strongest turn-promoters in cytoplasmic turns. These results suggest that the process of turn formation between transmembrane helices is different for lumenal and cytoplasmic turns.
Sääf
A
A
Department of Biochemistry, Stockholm University, Stockholm, S-106 91, Sweden.
Hermansson
M
M
von Heijne
G
G
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D003593:Cytoplasm / Q000737:chemistry / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000737:chemistry / Q000378:metabolism*; D006031:Glycosylation; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
D000596:Amino Acids; D008565:Membrane Proteins