Targeting of type II transmembrane proteins (H.-D. Schmitt)

Vesicle transport between Golgi and ER in yeast
Group leader: Hans Dieter Schmitt
Department of Neurobiology


	Members of our Group

xName

xphone number

xE-mail address: name(at)gwdg.de

xHans Dieter Schmitt,
PhD

x+49 +551 201 1652

xhschmit.....

Saskia Schröter

+49 +551 201 1714

sschroe4...

Peter Mienkus, technician

x+49 +551 201 1714

pmienku.....

SNARE proteins in membrane fusion
SNARE proteins in membrane fusion

xFormer members
xof the labxx

xpresent address

xSabrina Zink, PhD

University Marburg

xUwe Andag, PhD

xSartorius AG, Göttingen

xTanja (Neumann) Wulf

Agilent technologies

xCarmen Graf, PhD

University Göttingen

Research Interests

Proteins of the endoplasmic reticulum (=ER-resident proteins)
as well as proteins of the transport machinery cycle between Golgi and ER.
This recycling involves COP-I coated transport carriers.
We analyzed the recycling of Sec22p, a SNARE protein acting
in transport between the ER and Golgi.
(The function of SNAREs is illustrated in the little movie shown above).
We mainly employed genetic approaches using budding yeast
(Saccharomyces cerevisiae).

The two revolving pictures below show the effect of a recycling defect
on the loclaization of Sec22p

Missorting of Sec22p to the Golgi in yeasts with defects in Golgi-ER recycling

Green fluorescent Sec22p in wild type cells.

In normal cells GFP-Sec22p is concentrated in the endoplasmic
reticulum around the nucleus and under the plasma membrane.
A recycling machinery involving COP-I coated vesicles constantly
retrieves GFP-Sec22p from the Golgi.

Green fluorescent Sec22p in mutant cells.

The protein fails to be retrieved from the Golgi
in a ufe1-1 mutant.
(The Golgi cisternae in Saccharomyces cerevisiae
are randomly distributed within the cell.)

(Tanja [Neumann]Wulf , former member of the lab
and Rainer Heintzmann now at King’s College London)

We applied a synthetic lethal screen with sec22D (knock out) cells
to identify additional factors required for Golgi-ER retrieval.
One of the genes identified is DSL1. It encodes a protein that interacts
with the COP-I complex and the peripheral ER protein Tip20p.
The Dsl1 protein consists of three distinct domains:

An N-terminal domain that interacts with Tip20p.
A very acdic central domain with tandemly arranged tryptophan motifs.
These residues mediate the interaction with the COP-I vesicle coat
subunits d-COP and a/e-COP.
A conserved C-terminal domain which resembles the C-terminal domain of
ZW10 proteins from higher eukaryotes
(see "Supplemental Data" of Andag et al., 2003).

In a collaboration with the former lab of M. Gerard Waters we characterized Dsl3(Sec39)p,
an additional member of the 'Dsl1p complex'.
The whole complex consists of three large proteins, Dsl1p, Dsl3p and Tip20p
as well as three Q/t-SNAREs, Ufe1p, Sec20p and Use1p (see table below)
(Kraynack et al, 2005).
The complex is now considered to be a of eight so-called tethering complexes in yeast.
These tethers are large complexes that mediate the initial interaction between membranes
meant to fuse which each other.

The following table lists the subunits of the yeast 'Dsl1p complex' (Kraynack et al, 2005)
and the equivalent syntaxin 18 complex from rat (Hirose et al., 2004, EMBO J. 23:1267-78;
Aoki et al., 2009, MBC 20:2639-49).
Note that at steady state little Sly1p and Sec22p are associated with the yeast complex.)

	yeast 'Dsl1p complex'	mammals syntaxin 18 complex
peripheral	Dsl1p	ZW10
membrane	Dsl3(Sec39)p	NAG
proteins	Tip20p	RINT-1
	Sly1p	rSly1
	Sec20p	BNip1
Q/t-SNAREs	Ufe1p	syntaxin 18
	Use1p	p31/Use1
R/v-SNARE	Sec22p	Sec22b

In our most recent work we could show that COP-I coated Golgi-derived
vesicles accumulate at one specific site within Dsl1p-depleted cells.
The center of these vesicle clusters contain COP-II coated membranes,
suggesting that "ER access sites" are close to "ER entry sites".
The fact that coated vesicles accumulate may indicate that uncoating
can be linked to tethering. In our present work we try to get biochemical
evidence for that.


	Publications

Zink, S., Wenzel, D., Wurm, C.A., and Schmitt, H.D. (2009). A link between ER tethering and COP-I vesicle uncoating. Dev Cell 17:403-416

Li, Y.J., Schmitt, H.D., Gallwitz, D., and Peng, R.W. (2007). Mutations of the SM protein Sly1 resulting in bypass of GTPase requirement in vesicular transport are confined to a short helical region. FEBS Lett. 581:5698-5702.

Kraynack, B.A., Chan, A., Rosenthal, E., Essid, M., Umansky, B., Waters, M.G., and Schmitt, H.D. (2005). Dsl1p, Tip20p, and the Novel Dsl3(Sec39) Protein Are Required for the Stability of the Q/t-SNARE Complex at the Endoplasmic Reticulum in Yeast. Mol Biol Cell. 9, 3963-3977

Graf, C.T., Riedel, D., Schmitt, H.D., and Jahn, R. (2005). Identification of functionally interacting SNAREs by using complementary substitutions in the conserved '0' layer. Mol Biol Cell 16:2263-2274.

Andag, U. and Schmitt H.D. (2003) Dsl1p, an essential component of the Golgi-ER retrieval system in yeast, uses the same sequence motif to interact with different subunits of the COPI vesicle coat. J. Biol. Chem; 278: 51722-51734 ("Supplemental Data")

Dilcher, M., Veith, B., Chidambaram, S., Hartmann, E., Schmitt, H.D. and Fischer von Mollard G. (2003) Use1p is a yeast SNARE protein required for retrograde traffic to the ER. EMBO J. 22:3664-3674.

Rein, U., Andag, U., Duden, R., Schmitt, H.D. and Spang, A. (2002) ARF-GAP-mediated interaction between the ER-Golgi v-SNAREs and the COPI coat. J. Cell Biol. 157, 395-404.

Andag, U., Neumann, T. and Schmitt, H.D. (2001) The coatomer-interacting protein Dsl1p is required for Golgi-to-endoplasmic reticulum retrieval in yeast (2001) J. Biol. Chem. 276:39150-39160.

Ossig, R., Schmitt, H.D., de Groot, B., Riedel, D., Keränen, S., Ronne, H., Grubmüller, H. and Jahn, R. (2000) Exocytosis requires asymmetry in the central layer of the SNARE complex. EMBO J. 19:6000-6010.

Ballensiefen,W., D. Ossipov and H. D. Schmitt (1998) Recycling of the yeast v-SNARE Sec22p involves COPI-proteins and the ER transmembrane proteins Ufe1p and Sec20p. J. Cell Science, 111:1507-1520.

Boehm, J., F. Letourneur, W. Ballensiefen, D. Ossipov, C. Démollière and H. D. Schmitt (1997) Sec12p requires Rer1p for sorting to coatomer (COPI)-coated vesicles and retrieval to the ER. J. Cell Science, 110: 991-1003.

Joachim Füllekrug, Johannes Boehm, Tommy Nilsson, Gottfried Mieskes and Hans Dieter Schmitt (1997) Human Rer1 is localized to the Golgi apparatus and complements the deletion of the homologous Rer1p protein of S. cerevisiae. Eur. J. Cell.Biol. 74:31-40.


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