# Structural Analysis of the Mannose 6-Phosphate Receptors

> **NIH NIH R01** · MEDICAL COLLEGE OF WISCONSIN · 2021 · $614,643

## Abstract

Lysosomes perform degradative metabolism critical to many endocytic, phagocytic, and autophagic
processes. Cation-independent mannose 6-phosphate receptor (CI-MPR) plays a vital role in the
biogenesis of lysosomes by delivering ~60 different newly synthesized hydrolytic enzymes with
mannose 6-phosphate (M6P) on their N-glycans to lysosomes. Lysosomal storage diseases (LSDs)
are caused by mutations in lysosomal proteins, mainly enzymes, that result in defective catabolism
and substrate accumulation. Characteristic of the family of ~70 LSDs is their progressive and
debilitating nature due to their impact on multiple organ systems. Treatment is symptomatic for most
LSDs, with only 11 having FDA-approved therapies. CI-MPR's ability to internalize recombinant M6P-
containing enzymes delivered to patients by bi-weekly intravenous infusion forms the basis of enzyme
replacement therapy (ERT) for 9 of these therapies. However, structural knowledge of the interaction
between CI-MPR and its cargo of ~60 different lysosomal enzymes is lacking. CI-MPR also binds a
diverse set of extracellular non-M6P-containing ligands that mediate CI-MPR's tumor suppressor role
and regulation of cell growth and differentiation. CI-MPR regulates plasma insulin-like growth factor 2
(IGF2) levels, and binds three components of the plasminogen activation system, plasminogen,
urokinase-type plasminogen activator receptor (uPAR), and tissue-type PA (tPA). However, limited
information is available concerning the molecular basis for CI-MPR's interaction with plasminogen and
uPAR. Here we will expand upon our preliminary data that: 1) revealed the crystal structure of CI-
MPR's N-terminal region that houses several ligand binding sites, 2) showed the first structural view of
CI-MPR's entire extracellular region by high-resolution electron microscopy (EM), and 3) identified
conformational changes elicited by pH and ligand binding. The overall structure of CI-MPR's 2300-
residue extracellular region comprised of 15 domains will be determined alone and bound to ligands
using an integrated approach combining single particle EM, mass spectrometry, X-ray crystallography
and NMR spectroscopy. The first structure of a complex between CI-MPR and a lysosomal enzyme
(Aim 1), plasminogen (Aim 2), and uPAR (Aim 2) will be elucidated. Kinetic analyses and cell-based
assays will evaluate allosteric effects of each of CI-MPR's ligands (Aim 2). The mechanism of acidic
pH-dependent ligand dissociation, which is essential to the functioning of CI-MPR and other endocytic
receptors, will be probed using mutagenesis studies and NMR techniques (Aim 3). Our new rat model
of the LSD Fabry disease will be used to test novel lysosomal enzyme-IGF2 fusion constructs for their
ability to reduce substrate accumulation (Aim 4). These studies will provide insight for the design of
improved therapeutics for the treatment of LSDs, and novel inhibitors of plasminogen activation.

## Key facts

- **NIH application ID:** 10074560
- **Project number:** 5R01DK042667-27
- **Recipient organization:** MEDICAL COLLEGE OF WISCONSIN
- **Principal Investigator:** Nancy M. Dahms
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $614,643
- **Award type:** 5
- **Project period:** 1992-03-01 → 2023-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10074560

## Citation

> US National Institutes of Health, RePORTER application 10074560, Structural Analysis of the Mannose 6-Phosphate Receptors (5R01DK042667-27). Retrieved via AI Analytics 2026-05-21 from https://api.ai-analytics.org/grant/nih/10074560. Licensed CC0.

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