Transmembrane domain-dependent sorting of proteins to the ER and plasma membrane in yeast

Abstract

organelles: the plasma membrane (Sso1p and the closely MRC Laboratory of Molecular Biology, Hills Road, related Sso2p), an endosomal/pre-vacuolar compartment Cambridge CB2 2QH, UK (Pep12p), the cis-Golgi (Sed5p) and the endoplasmic 1 Corresponding author reticulum (ER) (Ufe1p) (Hardwick and Pelham, 1992;Aalto et al., 1993;Becherer et al., 1996; Lewis and Sorting of membrane proteins between compartments Pelham, 1996). t-SNAREs in different compartments are of the secretory pathway is mediated in part by their not highly conserved at the primary sequence level, transmembrane domains (TMDs). In animal cells, although they share common secondary structural features: TMD length is a major factor in Golgi retention. In they are C-terminally anchored, with the bulk of the yeast, the role of TMD signals is less clear; it has been protein being in the cytosol, and they contain three proposed that membrane proteins travel by default to stretches of heptad repeats which could form coiledthe vacuole, and are prevented from doing so by coil domains, the longest stretch being close to the cytoplasmic signals. We have investigated the targeting transmembrane domain (TMD). This region has been of the yeast endoplasmic reticulum (ER) t-SNARE shown to be crucial for the interaction of syntaxin with Ufe1p. We show that the amino acid sequence of the the incoming v-SNARE, synaptobrevin (Calakos et al., Ufe1p TMD is important for both function and ER 1994; Kee et al., 1995). targeting, and that the requirements for each areThe t-SNAREs, which 'define' a given compartment in distinct. Targeting is independent of Rer1p, the only that they determine which vesicles are able to fuse with candidate sorting receptor for TMD sequences curit, must be localized correctly in order to prevent aberrant rently known. Lengthening the Ufe1p TMD allows fusion of vesicles with the wrong compartment. They thus transport along the secretory pathway to the vacuole provide a model system for studying protein sorting, i.e. or plasma membrane. The choice between these desthey are a family of similar proteins which are targeted tinations is determined by the length and composition to diverse locations. t-SNAREs lack well-characterized of the TMD, but not by its precise sequence. A longer sorting signals, although we have shown previously that TMD is required to reach the plasma membrane in the localization of the Golgi t-SNARE, Sed5p, is influenced yeast than in animal cells, and shorter TMDs direct both by its TMD and by the cytoplasmic portion of the proteins to the vacuole. TMD-based sorting is therefore protein (Banfield et al., 1994). a general feature of the yeast secretory pathway, butThis study focuses on the ER t-SNARE, Ufe1p. In occurs by different mechanisms at different points. particular, we have investigated the importance of the

The Deubiquitinating Enzyme Ubp1 Affects Sorting of the ATP-binding Cassette-Transporter Ste6 in the Endocytic Pathway

“…As a general rule, the length of the TMDs increases from inside to outside, if one moves along the secretory pathway. The shortest TMDs are observed in ER proteins (ϳ16 aa) and the longest in plasma membrane proteins (ϳ25 aa) (Rayner and Pelham, 1997).…”

Characterization of Four Lectin-Like Receptor Kinases Expressed in Roots of Medicago truncatula. Structure, Location, Regulation of Expression, and Potential Role in the Symbiosis with Sinorhizobium meliloti

“…In studies in yeast (see Rayner and Pelham, 1997) and more recently in plants (Brandizzi et al, 2002), the length of the TM helix has been shown to play a major role in protein sorting because the helix needs to be at least 23 amino acids to span and to permit sorting to the PM. The predicted TM helices of MtLecRK1;1 and MtLecRK7;2 are 23 amino acids in length, thus fulfilling this sorting requirement.…”

Specific Retrieval of the Exocytic SNARE Snc1p from Early Yeast Endosomes

“…This allowed the initial sorting of the altered proteins into the exocytic or vacuolar pathway to be determined without the complication of subsequent endocytosis. It has previously been shown that the destination of membrane proteins leaving the yeast Golgi is affected by the length and composition of their TMDs (Rayner and Pelham, 1997). Snc1p has a TMD of 20 residues, shorter than is typical for plasma membrane proteins in yeast (Munro, personal communication), and to investigate its importance for targeting we prepared a number of chimeras with altered TMDs.…”