Distinguishing between calpain heterodimerization and homodimerization.

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Mammalian calpains are intracellular cysteine proteases crucial for cellular processes.
• Calpains 1 and 2 are heterodimers, but the dimerization preference of other calpains is unclear.
• The penta-EF-hand (PEF) domain mediates subunit interactions.

Purpose of the Study:

• To determine the dimerization preference (heterodimer vs. homodimer) of calpains 1, 3, 9, and 13.
• To understand the implications of dimerization for recombinant protein production and in vivo activity.
• To assess the potential for inhibition by calpastatin based on dimerization.

Main Methods:

• Differential tagging system utilizing His6 and antifreeze protein tags.
• Coexpression of PEF domains of various calpains with the small subunit's PEF domain.
• Analysis of dimerization patterns through protein interaction studies.

Main Results:

• Calpain 1 PEF domain heterodimerized with the small subunit PEF domain, as expected.
• Calpain 3 PEF domain predominantly formed a homodimer.
• Calpain 9 PEF domain heterodimerized with the small subunit, while calpain 13 PEF domain mainly formed a homodimer.

Conclusions:

• Calpain dimerization preference varies, with calpains 3 and 13 favoring homodimerization.
• Dimerization data informs recombinant calpain production strategies and predicts activity in knockout models.
• Homodimeric calpains 3 and 13 may be less susceptible to calpastatin inhibition due to their structure.