Calcium storage in multivesicular endo-lysosome

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Endo-lysosomes (late endosomes) are recognized as intracellular calcium stores alongside the endoplasmic reticulum.
• The mechanisms of calcium storage within endo-lysosomes remain largely uncharacterized, unlike the well-understood role of calcium-binding proteins in the endoplasmic reticulum.

Purpose of the Study:

• To investigate the role of endo-lysosomal membrane structure in cellular calcium storage.
• To elucidate the molecular mechanisms underlying calcium binding and storage within endo-lysosomes.

Main Methods:

• A theoretical approach was employed to model calcium storage capacity based on bilayer calcium binding affinities and endo-lysosome morphology.
• Experimental validation was performed using Sorting Nexin 3 depletion to alter intralumenal membrane content.

Main Results:

• The structural organization of endo-lysosomal membranes, particularly their multivesicular ultrastructure and extensive intralumenal membrane surface area, was identified as a key driver of calcium storage.
• Negatively charged lipids and proteins within the acidic endo-lysosomal environment were confirmed as the primary calcium-binding molecules.

Conclusions:

• The large surface area provided by intralumenal membranes in endo-lysosomes is essential for their calcium storage capacity.
• Acidic lipids and proteins within endo-lysosomes function as the main calcium-binding components in mammalian cells.