Allosteric regulation of lysosomal enzyme recognition by the cation-independent mannose 6-phosphate receptor

Linda J Olson,Mayumi Ishihara,Jung-Ja P Kim,Robert J Woods,Sandeep K Misra,Oliver C Grant,Joshua S Sharp,Michael Tiemeyer,Gang Ren,Kevin P Battaile,Nancy M Dahms,Amika Sood

doi:10.1038/s42003-020-01211-w

Abstract

The cation-independent mannose 6-phosphate receptor (CI-MPR, IGF2 receptor or CD222), is a multifunctional glycoprotein required for normal development. Through the receptor’s ability to bind unrelated extracellular and intracellular ligands, it participates in numerous functions including protein trafficking, lysosomal biogenesis, and regulation of cell growth. Clinically, endogenous CI-MPR delivers infused recombinant enzymes to lysosomes in the treatment of lysosomal storage diseases. Although four of the 15 domains comprising CI-MPR’s extracellular region bind phosphorylated glycans on lysosomal enzymes, knowledge of how CI-MPR interacts with ~60 different lysosomal enzymes is limited. Here, we show by electron microscopy and hydroxyl radical protein footprinting that the N-terminal region of CI-MPR undergoes dynamic conformational changes as a consequence of ligand binding and different pH conditions. These data, coupled with X-ray crystallography, surface plasmon resonance and molecular modeling, allow us to propose a model explaining how high-affinity carbohydrate binding is achieved through allosteric domain cooperativity.

Highlights

The cation-independent mannose 6-phosphate receptor (CI-MPR, IGF2 receptor or CD222), is a multifunctional glycoprotein required for normal development
The other carbohydrate recognition domains (CRDs) remains unoccupied in both structures, unlike bovine CI-MPR domains [1,2,3], where we showed domain 3 was bound to a ligand: either M6P or the oligosaccharide of a crystallographic neighbor (Fig. 1c, inset)[24,25]
Our X-ray crystal structures, coupled with small-angle X-ray scattering (SAXS), fast photochemical oxidation of proteins (FPOP), and surface plasmon resonance (SPR) analyses, allows us to propose an allosteric mechanism for the functioning of CI-MPR

Summary

Introduction

The cation-independent mannose 6-phosphate receptor (CI-MPR, IGF2 receptor or CD222), is a multifunctional glycoprotein required for normal development. CI-MPR, which is the primary receptor responsible for this intracellular trafficking[1], binds multiple ligands[3] at the cell surface that include M6Pcontaining cytokines[4] and non-M6P-containing molecules (e.g., insulin-like growth factor 2 (IGF2)[5], plasminogen[6], urokinasetype plasminogen activator receptor (uPAR)) to mediate CIMPR’s roles as a tumor suppressor[7] and regulator of cell growth and differentiation[8]. Given these many functions, it is not surprising that mice lacking the CI-MPR gene die at birth[9,10].

Methods

Results

Conclusion