Evolutionarily conserved multiple C2 domain proteins with two transmembrane regions (MCTPs) and unusual Ca2+ binding...

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• C2 domains are crucial in signal transduction and membrane trafficking proteins.
• Typically, C2 domains bind phospholipids in a calcium-dependent or independent manner to regulate protein function.
• Multiple C2 domain and transmembrane region proteins (MCTPs) represent a newly identified family of conserved C2 domain proteins.

Purpose of the Study:

• To characterize the novel family of multiple C2 domain and transmembrane region proteins (MCTPs).
• To investigate the calcium (Ca2+) and phospholipid binding properties of MCTP C2 domains.
• To determine the functional role of MCTP C2 domains in cellular processes.

Main Methods:

• Sequence analysis of MCTP genes across different organisms.
• Biochemical assays to assess Ca2+ and phospholipid binding affinities of MCTP C2 domains.
• Intrinsic tryptophan fluorescence spectroscopy to monitor Ca2+ titrations.

Main Results:

• MCTPs possess a unique structure with three C2 domains and two transmembrane regions.
• Despite a consensus sequence, MCTP C2 domains did not interact with phospholipids.
• All analyzed MCTP C2 domains exhibited high-affinity Ca2+ binding in the absence of phospholipids.

Conclusions:

• MCTPs are evolutionarily conserved proteins with C2 domains that function as Ca2+-binding modules.
• Unlike other C2 proteins, MCTP C2 domains are membrane-anchored and do not bind phospholipids.
• These findings reveal unusual Ca2+-dependent properties of MCTPs, distinct from canonical C2 domain functions.