FOLDING AND ASSEMBLY OF LDL RECEPTORS AND THEIR (CO-)CHAPERONES

PhD student project 2
(Early Stage Researcher 2, ESR2)

FOLDING AND ASSEMBLY OF LDL RECEPTORS AND THEIR (CO-)CHAPERONES

Supervision: Ineke Braakman

Early Stage Researcher: Anna Chatsisvili

       

Aim:
To establish the role and collaboration of (co-)chaperones in LDL receptor folding.

Methodology:
We aim to establish the molecular mechanism of collaborating (co-)chaperones in LDL receptor (LDLR) folding. We will construct a panel of LDLR disease mutants with variable folding defects, from strongly misfolded to mild. These will be expressed and their folding examined in cells with increased or decreased Grp94 and pERp1 (family member) expression to uncover the molecular mechanism of these folding factors' activities. Grp94 is an abundant ER-resident Hsp90 family chaperone, and pERp1 is the founding member of an abundant oxidoreductase family we identified, which resides in a complex with Grp94. Radioactive pulse-labeling will allow kinetic analysis of folding and maturation of the LDLR in intact cells. In addition we will purify Grp94 and the pERp1 family to establish whether and how they influence each other’s biological activities: ATPase activity and client binding for Grp94, oxidoreductase activity and client binding for the pERp1 family. LDLR fragments (LDL-A repeats for instance, or EGF repeats and beta-propeller) will be tested as possible clients for these folding factors.

Collaborators:
Gros, Rüdiger; Thomas (McGill); Nyken

Key publications:

1. A. van der Zand, J. Gent, I. Braakman*, H.F. Tabak* (2012) ‘Different vesicular routes from the endoplasmic reticulum combine to form peroxisomes.’ Cell 149: 397-409. *joint senior authors
2. F. Pena*, A. Jansens*, G. van Zadelhoff, I. Braakman (2010) Calcium as a crucial cofactor for low density lipoprotein receptor folding in the ER. J. Biol. Chem. 285: 8656-8664. *joint first authors
3. E. Van Anken., F. Pena, N. Hafkemeijer, C. Christis, E.P. Romijn, U. Grauschopf, V.M.J. Oorschot, T. Pertel, S. Engels, A. Ora, V. Lastun, R. Glockshuber, J. Klumperman, A.J.R. Heck, J. Luban, I. Braakman (2009) Efficient IgM assembly and secretion require the plasma cell induced ER protein pERp1. Proc Natl Acad Sci USA 106: 17019-17024.