View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Elsevier - Publisher Connector Biochimica et Biophysica Acta 1744 (2005) 438 – 454 http://www.elsevier.com/locate/bba Review Protein transport from the late Golgi to the vacuole in the yeast Saccharomyces cerevisiae Katherine Bowersa, Tom H. Stevensb,* aCambridge Institute for Medical Research and Department of Clinical, Biochemistry, University of Cambridge, Addenbrooke’s Hospital, Hills Road, Cambridge CB2 2XY, UK bInstitute of Molecular Biology, University of Oregon, Eugene, OR 97403-1229, USA Received 16 March 2005; received in revised form 15 April 2005; accepted 19 April 2005 Available online 11 May 2005 Abstract The late Golgi compartment is a major protein sorting station in the cell. Secreted proteins, cell surface proteins, and proteins destined for endosomes or lysosomes must be sorted from one another at this compartment and targeted to their correct destinations. The molecular details of protein trafficking pathways from the late Golgi to the endosomal system are becoming increasingly well understood due in part to information obtained by genetic analysis of yeast. It is now clear that proteins identified in yeast have functional homologues (orthologues) in higher organisms. We will review the molecular mechanisms of protein targeting from the late Golgi to endosomes and to the vacuole (the equivalent of the mammalian lysosome) of the budding yeast Saccharomyces cerevisiae. D 2005 Elsevier B.V. All rights reserved. Keywords: Vacuole protein sorting (VPS); Late Golgi; Multivesicular body (MVB); Endosome; Protein trafficking; Yeast 1. Introduction are defective for vacuolar segregation, and grd mutants are Golgi retention deficient [1–10]. There is significant One essential feature of eukaryotic cells is the presence overlap of the genes identified in these screens. For the of intracellular membrane-bound compartments or organ- purposes of this review, we will focus on the function of elles. Proteins must be targeted to the correct organelle for the VPS genes, and the proteins they encode (see their function, modification, and/or destruction. Genetic Table 1). analysis in yeast has been instrumental in determining the As can be seen from Fig. 1, there are several transport molecular details of protein trafficking pathways and over pathways from the yeast late Golgi compartment. There are 70 proteins involved in the steps of protein trafficking at least two types of vesicles that take proteins to the cell from the yeast late Golgi to the vacuole have now been surface for secretion from the cell or incorporation into the identified. Several large-scale screens have been employed plasma membrane: one is likely to be a direct route, and to find mutants defective in this process. For example, vps another via endosomes [11,12]. In addition, proteins may be (vacuolar protein sorting) mutants secrete the soluble sorted to endosomes via several pathways. Perhaps, the vacuolar hydrolase carboxypeptidase Y (CPY), vam best-characterised route from the late Golgi to the late mutants have abnormal vacuole morphology, pep mutants endosome or multivesicular body (MVB, also referred to as are defective for vacuolar protease activity, vac mutants the prevacuolar compartment) is named after its most studied cargo CPY. Another route takes proteins from the late Golgi, by-passing the endosomal network, to the * Corresponding author. vacuole, and is again named after its most studied cargo E-mail address: [email protected] (T.H. Stevens). protein, alkaline phosphatase [ALP, see Refs. [13–15]]. A 0167-4889/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.bbamcr.2005.04.004 K. Bowers, T.H. Stevens / Biochimica et Biophysica Acta 1744 (2005) 438–454 439 Table 1 Table 1 (continued) VPS genes Alias ORF Refs. Alias ORF Refs. designation designation Class E VPS genes Class A VPS genes VPS25 – YJR102C [3–5] 1 VPS8 FUN15 YAL002W [1–3,5,99] VPS27 GRD11, DID7, YNR006W [3,5,10,153] VPS10 PEP1 YBL017C [2,3,5,7] SSV17 VPS13 SOI1 YLL040C [2,3,5,31,178] VPS28 – YPL065W [3–5] VPS29 PEP11 YHR012W [2,3,5,7] VPS31 BRO1, LPF2, YPL084W [3,5,216–218] VPS30 APG6, ATG6 YPL120W [3,5,191,192] ASI6, NPI3 VPS35 GRD9 YJL154C [2,3,5,10] VPS32 SNF7, DID1 YLR025W [1,3,5,153,214] VPS38 – YLR360W [4,5,178] VPS36 VAC3, GRD12 YLR417W [4,5,9,10,178] VPS55 – YJR044C [8,188] VPS37 SRN2, SRN10 YLR119W [4,5,219,220] VPS63* – YLR261C [8] VPS44 NHX1, NHA2 YDR456W [5,127,158,221] VPS70 – YJR126C [8] VPS46 DID2, FTI1, CHM1 YKR035W-A [5,130,153,212] VPS74 API1 YDR372C [8] VPS60 MOS10, CHM5 YDR486C [133,212,222] Class B VPS genes Class F VPS genes VPS5 PEP10, GRD2 YOR069W [2,3,5,7,10] VPS1 GRD1, LAM1, SPO15 YKR001C [1,3,5,10,59,223] VPS17 PEP21 YOR132W [2,3,5] VPS26 PEP8, GRD6 YJL053W [2,5,7,10] VPS39 VAM6, CVT4 YDL077C [4–6,193] VPS62 – YGR141W [8] VPS41 VAM2, CVT8, YDR080W [5,6,193–195] VPS65 – YLR322W [8] FET2, SVL2 VPS68 – YOL129W [8] VPS43 VAM7 YGL212W [5,6] VPS711 SWC6 YML041C [8,203] VPS51 VPS67, WHI6, API3 YKR020W [184,196,197] VPS genes and their alternative names are shown. Two sets of initial screens VPS52 SAC2 YDR484W [183,198] were performed to identify vps mutants. One set identified vpt mutants VPS53 – YJL029C [183] [2,3], and the other vpl mutants [1,4,5]. Complementation testing and VPS54 LUV1, CGP1, TCS3 YDR027C [183,199–201] renaming generated the VPS nomenclature [see Ref. [5]], and hence the vpt VPS61* – YDR136C [8] and vpl names have been omitted. Other names, as shown in the VPS64 FAR9 YDR200C [8,202] Saccharomyces genome database [190], are included. 1VPS8 and VPS71 VPS66 – YPR139C [8] have been put into two classes. *Denotes open reading frames that may not VPS69* – YPR087W [8] encode proteins (dubious ORFs) and that when deleted are likely to affect VPS711 SWC6 YML041C [8,203] neighbouring genes involved in CPY trafficking [8,190]. VPS72 SWC2 YDR485C [8,203] VPS73 – YGL104C [8] third route takes proteins from the late Golgi to early VPS75 – YNL246W [8] endosomes [16,17]. Class C VPS genes VPS11 PEP5, END1, YMR231W [3–7,18,204] VAM1 2. Vacuolar protein sorting mutants VPS16 VAM9, SVL6 YPL045W [3,5,6,18,194] VPS18 PEP3, VAM8 YLR148W [3,5–7,18] VPS33 PEP14, VAM5, YLR396C [3,5–7,18,205–207] 2.1. vps mutants secrete the soluble hydrolase CPY and are MET27, CLS14, classified based on vacuolar morphology SLP1 CPY is synthesized as a prepro form and is transported Class D VPS genes across the endoplasmic reticulum (ER) membrane. Follow- VPS3 PEP6 YDR495C [1,3,5,7] VPS6 PEP12 YOR036W [1,3,5,7] ing signal peptidase cleavage in the ER to produce a 67 kDa VPS81 FUN15 YAL002W [1–3,5,99] precursor (p1) form, it is transported through the Golgi VPS9 – YML097C [3,5] where it acquires sugar modifications to become a 69 kDa VPS15 VAC4, GRD8 YBR097W [3–5,9,10] (p2) form. In wild-type cells, CPY is transported to the VPS19 PEP7, VAC1 YDR323C [3,5,7,9] vacuole where it is processed to a 61 kDa mature form. VPS21 YPT51 YOR089C [3,5,208] VPS34 PEP15, END12 YLR240W [1,3,5,7,209] However, in vps mutant cells, a portion of the p2 (Golgi) VPS45 STT10 YGL095C [5,210] form of CPY is secreted from the cell. There are currently 61 yeast VPS genes (see Table 1), and the majority of these Class E VPS genes have been identified in screens designed to find mutants that VPS2 REN1, GRD7, YKL002W [1,3,5,153,211,212] secrete CPY [1–5,8]. It should be noted that whereas all vps DID4, CHM2 VPS4 END13, DID6, YPR173C [1,3,5,10,153, mutants secrete CPY, there are many other mutants that GRD13, CSC1 209,213] secrete low levels of this protein. For example, a recent VPS20 CHM6 YMR077C [3–5,212] screen of the yeast genome deletion collection identified VPS22 SNF8 YPL002C [3–5,214] 146 genes that when deleted caused CPY secretion [8]. VPS23 STP22 YCL008C [3–5,215] These included the previously identified VPS genes, many VPS24 DID3 YKL041W [3,5,153] genes involved in other cellular processes, and some 440 K. Bowers, T.H. Stevens / Biochimica et Biophysica Acta 1744 (2005) 438–454 Table 2 Classification of vps mutants Class Vacuolar morphology A Wild-type: 3–10 spherical vacuoles that cluster in one area of the cytoplasm. In dividing cells, the vacuole extends from mother to daughter cell along the cell axis. B Fragmented vacuoles: more than 20 small, vacuole-like compartments. C No identifiable vacuoles. D Single, large vacuole that fails to extend into daughter cell buds. E Vacuoles larger than wild-type, with a very large, aberrant late endosome/MVB or prevacuolar compartment (the class E compartment) adjacent to the vacuoles. F One large vacuole surrounded by a number of fragmented vacuolar structures. For further details, see Ref. [5]. Fig. 1. Protein trafficking pathways from the late Golgi to the vacuole in endosome, CPY dissociates from Vps10p and Vps10p is yeast. There are multiple protein transport pathways from the late Golgi. Proteins can be secreted or targeted to the cell surface, or transported to returned to the late Golgi via a retrograde transport pathway early endosomes (EE). In addition, the CPY pathway takes proteins via the that requires the retromer complex and probably Vps1p late endosome/multivesicular body (MVB) to the vacuole. The CPY [23,24]. CPY is transported to the vacuole where it is pathway and endocytic pathways converge at or before the late endosome/ proteolytically activated to its mature form.