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Vol. 20, Issue 24, 5276-5289, December 15, 2009

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The CORVET Subunit Vps8 Cooperates with the Rab5 Homolog Vps21 to Induce Clustering of Late Endosomal Compartments

Daniel F. Markgraf^*,, Franziska Ahnert^*,, Henning Arlt^*,, Muriel Mari^,, Karolina Peplowska^*,||, Nadine Epp^*, Janice Griffith, Fulvio Reggiori, and Christian Ungermann^*

*University of Osnabrück, Department of Biology, Biochemistry Section, 49076 Osnabrück, Germany; and University Medical Centre Utrecht, Department of Cell Biology, and Institute of Biomembranes, 3584 CX Utrecht, The Netherlands

Submitted June 24, 2009; Revised September 11, 2009; Accepted October 6, 2009
Monitoring Editor: Patrick J. Brennwald

Membrane tethering, the process of mediating the first contact between membranes destined for fusion, requires specialized multisubunit protein complexes and Rab GTPases. In the yeast endolysosomal system, the hexameric HOPS tethering complex cooperates with the Rab7 homolog Ypt7 to promote homotypic fusion at the vacuole, whereas the recently identified homologous CORVET complex acts at the level of late endosomes. Here, we have further functionally characterized the CORVET-specific subunit Vps8 and its relationship to the remaining subunits using an in vivo approach that allows the monitoring of late endosome biogenesis. In particular, our results indicate that Vps8 interacts and cooperates with the activated Rab5 homolog Vps21 to induce the clustering of late endosomal membranes, indicating that Vps8 is the effector subunit of the CORVET complex. This clustering, however, requires Vps3, Vps16, and Vps33 but not the remaining CORVET subunits. These data thus suggest that the CORVET complex is built of subunits with distinct activities and potentially, their sequential assembly could regulate tethering and successive fusion at the late endosomes.

These authors contributed equally to this work.

Present addresses: Harvard Medical School, Boston, MA 02115;

^||Max-Planck Institute of Biochemistry, 82152 Martinsried, Germany.

Address correspondence to: Christian Ungermann (christian.ungermann{at}biologie.uni-biologie.de) or Fulvio Reggiori (F.Reggiori{at}umcutrecht.nl).

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