The continuing disappearance of "pure" Ca2+ buffers

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Physiology

Background:

• Calcium ions (Ca2+) are critical intracellular messengers involved in numerous cellular processes.
• EF-hand Ca(2+)-binding proteins, including parvalbumins, calbindins, and calretinin, play vital roles in Ca2+ signaling and homeostasis.
• The human genome encodes over 240 identified EF-hand Ca(2+)-binding proteins, forming a complex Ca(2+) homeostasome.

Purpose of the Study:

• To advance the understanding of Ca(2+)-binding proteins, commonly known as Ca(2+) buffers.
• To differentiate between Ca(2+) buffering and Ca(2+) sensing functions within this protein family.
• To identify which specific Ca(2+)-binding proteins function exclusively as buffers.

Main Methods:

• Review and synthesis of recent accumulated data on EF-hand Ca(2+)-binding proteins.
• Analysis of studies utilizing transgenic animal models.
• Functional characterization of protein families like parvalbumins, calbindins, and calretinin.

Main Results:

• Recent findings suggest that calbindin-D28k, calretinin, and oncomodulin possess additional Ca(2+) sensor functions.
• Parvalbumins and calbindin-D9k are identified as the only proteins within this group that exclusively function as Ca(2+) buffers.
• These proteins operate within a complex network of cellular mechanisms regulating Ca(2+) signaling and homeostasis.

Conclusions:

• The functional roles of Ca(2+)-binding proteins are more diverse than previously assumed.
• A distinction is emerging between proteins acting purely as Ca(2+) buffers and those with dual buffering and sensing capabilities.
• Understanding these distinct roles is crucial for comprehending Ca(2+) signaling and maintaining cellular homeostasis.