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Membrane proteins depend on complex translocation machineries for insertion into target membranes. Although it has long been known that an abundance of nonpolar residues in transmembrane helices is the principal criterion for membrane insertion, the specific sequence-coding for transmembrane helices has not been identified. By challenging the endoplasmic(More)
Barley Mlo defines the founder of a novel class of plant integral membrane proteins. Lack of the wild type protein leads to broad spectrum disease resistance against the pathogenic powdery mildew fungus and deregulated leaf cell death. Scanning N-glycosylation mutagenesis and Mlo-Lep fusion proteins demonstrated that Mlo is membrane-anchored by 7(More)
We have recently reported a first experimental turn propensity scale for transmembrane helices. This scale was derived from measurements of how efficiently a given residue placed in the middle of a 40 residue poly(Leu) stretch induces the formation of a "helical hairpin" with two rather than one transmembrane segment. We have now extended these studies, and(More)
As proteins are integrated into the membrane of the endoplasmic reticulum, some hydrophilic polypeptide segments are transported through the translocation channel, others remain in the cytosol, and hydrophobic transmembrane sequences are released into the lipid phase. We have addressed the molecular mechanism by which these events occur. We demonstrate that(More)
Signal peptides (SPs) target proteins to the secretory pathway and are cleaved from the nascent chain once the translocase in the ER has been engaged. Signal-anchor (SA) sequences also interact transiently with the ER translocase, but are not cleaved and move laterally out of the translocase to become permanent membrane anchors. One obvious difference(More)
By analogy to mammals, odorant receptors (ORs) in insects, such as Drosophila melanogaster, have long been thought to belong to the G-protein coupled receptor (GPCR) superfamily. However, recent work has cast doubt on this assumption and has tentatively suggested an inverted topology compared to the canonical N(out) - C(in) 7 transmembrane (TM) GPCR(More)
Positively charged residues located near the cytoplasmic end of hydrophobic segments in membrane proteins promote membrane insertion and formation of transmembrane alpha-helices. A quantitative understanding of this effect has been lacking, however. Here, using an in vitro transcription-translation system to study the insertion of model hydrophobic segments(More)
We have measured the minimum number of residues in a translocating polypeptide required to bridge the distance between the P-site in endoplasmic reticulum-bound ribosomes and the lumenally disposed active site of the oligosaccharyl transferase. The results suggest that a nascent chain may traverse the ribosome/translocase complex in a largely extended(More)
We have studied the membrane insertion of ProW, an Escherichia coli inner membrane protein with seven transmembrane segments and a large periplasmic N-terminal tail, into endoplasmic reticulum (ER)-derived dog pancreas microsomes. Strikingly, significant levels of N-tail translocation is seen only when a minimum of four of the transmembrane segments are(More)
Integral membrane proteins are integrated cotranslationally into the membrane of the endoplasmic reticulum in a process mediated by the Sec61 translocon. Transmembrane α-helices in a translocating polypeptide chain gain access to the surrounding membrane through a lateral gate in the wall of the translocon channel [van den Berg B, et al. (2004) Nature(More)