Calcium negatively regulates meprin β activity and attenuates substrate cleavage

Area of Science:

• Biochemistry
• Molecular Biology
• Neuroscience

Background:

• Meprin β metalloproteinase is vital for extracellular matrix turnover, inflammation, and neurodegeneration.
• Previous research indicated calcium diminishes meprin β substrate cleavage, but the mechanism remained unclear.

Purpose of the Study:

• To elucidate the mechanism by which calcium influences meprin β activity.
• To investigate the role of a potential calcium binding site in meprin β structure and function.

Main Methods:

• Utilized a fluorogenic peptide assay and human amyloid precursor protein as substrates.
• Analyzed crystal structures of pro- and mature meprin β.
• Introduced mutations (D204A, D245A) in potential calcium-binding residues and assessed proteolytic activity and cellular localization.

Main Results:

• Calcium's effect on meprin β is direct, likely mediated by a specific binding site.
• Mutation D245A resulted in inactive, misfolded meprin β.
• Mutation D204A led to constitutive maturation, impaired cell surface transport, and increased β-secretase activity, causing Aβ-peptide accumulation.

Conclusions:

• Calcium binding to meprin β is essential for proper propeptide folding and protease inhibition.
• Disruption of calcium binding, as seen in D204A, can lead to misfolding and altered enzymatic activity, potentially impacting neurodegenerative diseases like Alzheimer's.
• Physiological calcium concentrations in the endoplasmic reticulum may be critical for meprin β function.