Membrane traffic in the late endocytic pathway
Delivery of endocytosed macromolecules to endolysosomes and the regeneration of lysosomes are essential for cellular health, metabolism as well as both susceptibility and resistance to infection. In mammalian cells, lysosomes are small membrane bound organelles ~0.5µm diameter, which are full of proteases and other hydrolytic enzymes and have long been regarded as the terminal compartment of the endocytic, phagocytic and autophagic pathways. We have found that the terminal compartment of the endocytic pathway is made up of acidic endolysosomes in which acid hydrolases, including cathepsins B, C and L, are catalytically active and acid hydrolase-inactive, neutral, terminal storage lysosomes. The latter kiss and fuse with late endosomes (also known as multivesicular bodies) to form endolysosomes. Live cell microscopy experiments have shown that activation of the acid hydrolases always occurs after kissing commences, with a time lag of ~2-4 min. Endolysosomes digest endocytosed macromolecules, can signal to the nucleus and are transient intracellular compartments from which storage lysosomes are reformed. We study the membrane traffic machinery of the late endocytic pathway, including the role of the ESCRT (endosomal sorting complex required for transport), HOPS ((homotypic fusion and vacuole protein sorting) and SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complexes, as well as ion channels and the multifunctional protein VARP (Vps9 and ankyrin repeat containing protein), which regulates the function of the SNARE protein, VAMP7. We aim to understand the coordination of fusion and fission events in the lysosome regeneration cycle linking endolysosomes and terminal storage lysosomes as well as the disruption of this cycle that occurs in some diseases. We collaborate with David Owen to integrate the structural and cell biology of the membrane traffic machinery functioning in the late endocytic pathway.
Wartosch, L.*, Günesdogan, U., Graham, S.C. & Luzio, J.P.* Recruitment of VPS33A to HOPS by VPS16 is required for lysosome fusion with endosomes and autophagosomes. Traffic doi:10.1111/tra.12283 *equal corresponding authors (2015).
Hesketh, G.G., Pérez-Dorado, I., Jackson, L.P., Wartosch, L., Schäfer, I. B., Gray, S.R., McCoy, A.J., Zeldin, O.B., Garman, E.F., Harbour, M.E., Evans, P.R., Seaman, M.N.J.*, Luzio, J.P. * & Owen, D.J.* VARP is recruited on to endosomes by direct interaction with retromer, where together they function in export to the cell surface. Dev. Cell 29, 591-606. * equal last authors (2014).
Luzio, J.P., Hackmann, Y., Dieckmann, N.M.G. & Griffiths, G.M. The Biogenesis of Lysosomes and Lysosome-Related Organelles. Cold Spring Harbor Perspect. Biol. 6, a016840. (2014)
Graham, S.C.*, Wartosch, L., Gray, S.R., Scourfield, E.J., Deane, J.E., Luzio, J.P.* and Owen, D.J. Structural basis of Vps33A recruitment to the human HOPS complex by Vps16. Proc. Natl Acad. Sci. USA 110, 13345–13350 *equal corresponding authors (2013).
Kent, H.M., Evans, P.R., Schäfer, I. B., Gray, S.R., Sanderson, C.M., Luzio, J.P. *, Peden, A.A. * and Owen, D.J. * Structural basis of the intracellular sorting of the SNARE VAMP7 by the AP-3 adaptor complex. Dev. Cell 22, 979–988 *equal last authors (2012).
Schäfer, I. B., Hesketh, G.G., Bright, N.A., Gray, S.R., Pryor, P.R., Evans, P.R., Luzio, J.P. * and Owen, D.J. * The binding of Varp to VAMP7 traps VAMP7 in a closed, fusogenically inactive conformation. Nature Struct. Mol. Biol. 19, 1300–1309 *equal last authors (2012).