Seven Novel Mammalian SNARE Proteins Localize to Distinct Membrane Compartments

Abstract

Soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) proteins of the vesicle-associated membrane protein (VAMP) and syntaxin families play a central role in vesicular trafficking through the formation of complexes between proteins present on vesicle and target membranes. Formation of these complexes is proposed to mediate aspects of the specificity of vesicle trafficking and to promote fusion of the lipid bilayers. In order to further understand the molecular mechanisms that organize membrane compartments, we have characterized seven new mammalian proteins of the VAMP and syntaxin families. The proteins are broadly expressed; however, syntaxin 13 is enriched in brain and VAMP 8 in kidney. The seven novel SNAREs localize in distinct patterns overlapping with Golgi, endosomal, or lysosomal markers. Our studies support the hypothesis that evolutionary radiation of these two gene families gave rise to sets of proteins whose differential expression and combinatorial associations define and organize the membrane compartments of cells.The distribution and restriction of molecules to membrane compartments is an essential process of eukaryotic cells. Distinct organelles of the secretory pathway are synthesized and maintained by budding of transport vesicles from a donor compartment followed by fusion of these vesicles with an acceptor membrane (1). The molecular mechanisms responsible for vesicle biogenesis, protein sorting, and membrane fusion are not yet fully understood. While yeast genetics, in vitro biochemistry, and studies of synaptic vesicles have identified many of the components essential for these processes (2-4), the full repertoire of important proteins and their mechanisms of action are yet to be determined. One particularly interesting issue is how a vesicle loaded with specific cargo recognizes the appropriate target. It is becoming clear that several independent mechanisms contribute to the specificity of vesicle trafficking, and it is the sum of these multiple layers of specificity that results in a process with high fidelity (5).A vesicle-target membrane recognition event mediated by interaction of integral membrane proteins of the vesicle (vSNAREs) 1 and target (t-SNAREs) membranes represents one layer of targeting specificity, acting at the final step of membrane fusion (6, 7). This process has been extensively studied in the mammalian presynaptic nerve terminal, where formation of a heterotrimeric complex between the v-SNARE, VAMPs 1 or 2, and the t-SNAREs syntaxin 1 and SNAP-25 is thought to serve as a membrane recognition mechanism and may drive fusion of the lipid bilayers (8, 9). These proteins have subsequently been found to be prototypic members of gene families that span species as well as membrane compartments (6). For example, syntaxin homologs in yeast have been localized to the Golgi (Sed5p) (10), endosomes (Pep12p) (11), lysosomes (Vam3p) (12), and the plasma membrane (Sso1p and Sso2p) (13). In particular, the SNAREs present on yeast vacuoles have been extensivel...

Distinct molecular mechanisms and divergent endocytotic pathways of AMPA receptor internalization

“…The simplest explanation for this difference in kinetics is that AMPA receptors that are internalized in response to insulin return more slowly to the surface. This hypothesis is consistent with our finding that AMPA receptors internalized in response to AMPA, but not in response to insulin, remain largely within a recycling endosome system, as defined by colocalization with EEA1, syntaxin 13 and TfR [32][33][34][35][36][37][38][39][40] . Unlike AMPA, insulin caused a divergence of internalized AMPA receptors out of the pathway delineated by EEA1, syntaxin 13 and TfR into a separate intracellular compartment.…”

“…6g and h), which goes through a recycling endosomal pathway, or with syntaxin 13 (Fig. 6i and j) 32 , a SNARE protein localized in tubulovesicular recycling endosomes 33 . Neither AMPA-nor insulin-induced internalized AMPA receptors colocalized with the lysosomal marker LAMP1 even after 30 minutes (Fig.…”

Human munc13 Is a Diacylglycerol Receptor that Induces Apoptosis and May Contribute to Renal Cell Injury in Hyperglycemia

“…The Golgi apparatus is involved in vesicular traffic. A number of SNARE proteins, such as yeast Sed5p (Banfield et al, 1994) and mVps45 (Tellam et al, 1997), mammalian syntaxin 6 (Bock et al, 1997), VAMP4, Syntaxin 13, and mVtib (Advani et al, 1998), have all been reported to be localized to the Golgi. Rat munc13-1 has been shown to interact with a number of proteins involved in vesicle docking and trafficking, such as syntaxin (Betz et al, 1997) and Doc2 (Orita et al, 1997).…”

Adult bone marrow stromal stem cells express germline, ectodermal, endodermal, and mesodermal genes prior to neurogenesis

“…Simultaneously, endodermal ceruloplasmin, expressed at high levels in liver and lung (Fleming and Gitlin, 1990), is transcribed in uncommitted MSCs. Likewise, ectodermal syntaxin 13, highly enriched in the brain (Advanti et al, 1998), and brain-specific aldolase C (Mukai et al, 1991) are expressed by MSCs. NMDA glutamate binding protein (Kumar et al, 1991) and APP (Shivers et al, 1988) represent additional neural genes transcribed by MSCs.…”