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Published on: October 4, 2017
Glycosylation of skeletal calsequestrin: implications for its function
Emiliano J Sanchez1, Kevin M Lewis, Gerhard R Munske
1School of Molecular Biosciences, Washington State University, Pullman, Washington 99164-4660, USA.
The Journal of Biological Chemistry
|December 16, 2011
Summary
Glycosylation of calsequestrin (CASQ) dynamically regulates its Ca(2+) binding and polymerization in the sarcoplasmic reticulum (SR). Mannose trimming ensures CASQ mobility and proper polymer formation, crucial for Ca(2+) buffering.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Calsequestrin (CASQ) is the primary Ca(2+) storage protein in the sarcoplasmic reticulum (SR).
- Native CASQ1 purified from skeletal muscle is glycosylated, impacting its function.
- Understanding CASQ glycosylation is key to its role in Ca(2+) homeostasis.
Purpose of the Study:
- To determine the specific site and degree of glycosylation of native rabbit CASQ1.
- To investigate the functional impact of glycosylation on CASQ properties by comparing native and recombinant forms.
- To elucidate the role of glycosylation in CASQ trafficking, polymerization, and Ca(2+) binding.
Main Methods:
- Comparative analysis of native glycosylated and recombinant non-glycosylated rabbit CASQ1.
- Utilized crystal structures, Ca(2+) binding capacity assays, analytical ultracentrifugation, and light-scattering.
- Investigated glycan mannose trimming during ER to SR trafficking.
Main Results:
- Confirmed specific glycosylation sites and degree on native CASQ1.
- Demonstrated that high mannose glycans (GlcNAc(2)Man(9)) hinder CASQ polymerization, ensuring mobility.
- Showed that trimmed glycans (GlcNAc(2)Man(1-4)) stabilize CASQ interfaces, enabling polymer formation and Ca(2+) binding in the SR.
- Proposed a molecular mechanism for the CPVT2 mutation (K206N) based on high-resolution structures.
Conclusions:
- Glycosylation plays a dynamic, regulatory role in CASQ function, controlling its polymerization and Ca(2+) buffering capacity.
- Mannose trimming of CASQ glycans is essential for its proper trafficking and assembly into functional Ca(2+) storage polymers within the SR.
- The study provides structural insights into CASQ glycosylation and a potential mechanism for a cardiac arrhythmia mutation.
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