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J Mol Biol. 2019 Mar 1;431(5):1038-1047. doi: 10.1016/j.jmb.2019.01.027. Epub 2019 Jan 25.

Progranulin Stimulates the In Vitro Maturation of Pro-Cathepsin D at Acidic pH.

Author information

1
Department of Neurology, University of California, San Francisco, CA 94143, USA.
2
Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94143, USA.
3
Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94143, USA; Pharmaceutical Sciences and Pharmacogenomics Graduate Program, University of California, San Francisco, CA 94143, USA.
4
Department of Pharmaceutical Chemistry, University of California, San Francisco, CA 94143, USA. Electronic address: matt.jacobson@ucsf.edu.
5
Department of Neurology, University of California, San Francisco, CA 94143, USA. Electronic address: aimee.kao@ucsf.edu.

Abstract

Single-copy loss-of-function mutations in the progranulin gene (PGRN) underlie the neurodegenerative disease frontotemporal lobar degeneration, while homozygous loss-of-function of PGRN results in the lysosomal storage disorder neuronal ceroid lipofuscinosis. Despite evidence that normal PGRN levels are critical for neuronal health, the function of this protein is not yet understood. Here, we show that PGRN stimulates the in vitro maturation of the lysosomal aspartyl protease cathepsin D (CTSD). CTSD is delivered to the endolysosomal system as an inactive precursor (proCTSD) and requires sequential cleavage steps via intermediate forms to achieve the mature state (matCTSD). In co-immunoprecipitation experiments, PGRN interacts predominantly with immature pro- and intermediate forms of CTSD. PGRN enhances in vitro conversion of proCTSD to matCTSD in a concentration-dependent manner. Differential scanning fluorimetry shows a destabilizing effect induced by PGRN on proCTSD folding (∆Tm = -1.7 °C at a 3:1 molar ratio). We propose a mechanism whereby PGRN binds to proCTSD, destabilizing the propeptide from the enzyme catalytic core and favoring conversion to mature forms of the enzyme. Further understanding of the role of PGRN in CTSD maturation will assist in the development of targeted therapies for neurodegenerative disease.

KEYWORDS:

cathepsin D; maturation; neurodegeneration; progranulin; propeptide

PMID:
30690031
PMCID:
PMC6613950
[Available on 2020-03-01]
DOI:
10.1016/j.jmb.2019.01.027

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