Two Structural and Functional Domains of MESD Required for Proper Folding and Trafficking of LRP5/6

Abstract

SUMMARY How the ER folding machinery coordinates general and specialized chaperones during protein translation and folding remains an important unanswered question. Here, we show two structural domains in MESD, a specialized chaperone for LRP5/6, carry out dual functions. The chaperone domain forms a complex with the immature receptor, maintaining the β-propeller domain in an interaction competent state for EGF-repeat binding. This promotes proper folding of the BP domain, causing a binding switch from the chaperone domain to the escort domain. The escort complex ensures LRP5/6 safe-trafficking from the ER to the Golgi by preventing premature ligand-binding. Inside the Golgi, the BP domain may contain a histidine switch, regulating MESD dissociation and retrieval. Together, we generate a plausible cell biology picture of the MESD/LRP5/6 pathway, suggesting that it is the specialized chaperones, MESD, that serves as the folding template to drive proper folding and safe trafficking of large multi-domain proteins LRP5/6.

The C-Terminal Region Mesd Peptide Mimics Full-Length Mesd and Acts as an Inhibitor of Wnt/β-Catenin Signaling in Cancer Cells

“…Our results of binding assays are consistent with recent NMR study on the full-length Mesd [24], which shows that the C-terminal flexible helical domain (156–195) is structurally distinct from the core domain (1–155), and is responsible for the escort function of Mesd by binding to LRP5/6. Nevertheless, peptides can have significant structural changes when isolated from proteins.…”

“…By performing molecular dynamics simulations on Mesd C-terminal region peptides, we demonstrated that the two LRP5/6 binding sites within the Mesd C-terminal region peptide form a positive surface consisted of the solvent exposed sidechains of positively charged residues. Our findings are consistent with a previous study of the NMR structure of Mesd and the cell surface LRP6 binding of Mesd mutants, which showed that the positively charged residues within Mesd C-terminal region are important for Mesd binding to LRP6 at the cell surface [24].…”

A Secreted Tyrosine Kinase Acts in the Extracellular Environment

“…In the cases of the ER chaperones MESD and ERP29, the tyrosines that we have found to be phosphorylated are each established to have an essential role in the interaction of these chaperones with specific substrates (Barak et al, 2009; Chen et al, 2010; Chen et al, 2011), also indicating a role for phosphorylation in the modulation of core protein function. Kinoshita et al previously reported that ectopic VLK expression reduced the overall rate of VSVG progression through the secretory pathway (Kinoshita et al, 2009), but this effect was seen equally with expression of wt VLK and VLK KM , the latter of which we have found to be inactive as a protein kinase.…”

Aggregates, Crystals, Gels, and Amyloids: Intracellular and Extracellular Phenotypes at the Crossroads of Immunoglobulin Physicochemical Property and Cell Physiology

“…Moreover, similar to the endosomal trafficking system, compartmental pH gradients also exist in the secretory pathway. In fact, by taking advantage of a pH gradient from the ER to the Golgi compartment, the functions of some resident proteins are intricately tied to the compartmental pH difference [218–220]. Detailed studies on the biosynthesis of pH-sensitive antibodies have not been reported to date, but the group of histidine-engineered IgGs may turn out to serve as a unique tool for cell biologists to probe unexplored functions of the secretory pathway organelles.…”