The IP3 receptor/Ca2+ channel and its cellular function.

Area of Science:

• Molecular and Cellular Biology
• Neuroscience
• Developmental Biology

Background:

• The inositol 1,4,5-trisphosphate receptor (IP3R) is crucial for intracellular calcium (Ca2+) release from the endoplasmic reticulum (ER).
• The P400 protein, known to be deficient in certain mutant mice, was extensively studied.
• Understanding IP3R function is vital for various physiological processes.

Purpose of the Study:

• To identify and characterize the P400 protein as an IP3R.
• To elucidate the structural and functional properties of IP3R.
• To investigate the role of IP3R in development, neuronal function, and exocrine secretion.

Main Methods:

• Protein purification and primary sequence determination of IP3R.
• Functional reconstitution of purified IP3R into lipid bilayers to study Ca2+ release.
• Overexpression studies, antibody inhibition assays, and cryo-electron microscopy (cryo-EM) and X-ray crystallography for structural analysis.
• Studies on mutant mice and analysis of protein interactions (e.g., ERp44, IRBIT).

Main Results:

• P400 was identified as an IP3R, and its primary sequence was determined.
• Purified IP3R functions as a Ca2+ release channel, with activity modulated by expression levels and antibody binding.
• IP3R is implicated in fertilization, embryonic development (dorso-ventral axis formation), neuronal plasticity, and exocrine functions (saliva and gastric juice secretion).
• Structural studies revealed unique features, including multiple cavities and dynamic conformational changes. ERp44 and IRBIT were identified as regulatory binding partners.

Conclusions:

• IP3R is a multifunctional protein essential for Ca2+ signaling, cellular development, and physiological processes.
• The structural plasticity and unique interaction partners of IP3R highlight its complex regulatory mechanisms.
• Further research into IP3R function can provide insights into various diseases and therapeutic strategies.