Calmodulin

Calmodulin

Error creating thumbnail:

Calmodulin

Calmodulin (CaM) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an essential component of the calcium signal transduction pathway, where it acts as a calcium sensor and signal transducer. Calmodulin is involved in a wide range of cellular processes, including muscle contraction, intracellular movement, cell division, and the regulation of metabolic pathways.

Structure

Calmodulin is a small, highly conserved protein composed of 148 amino acids. It has a dumbbell-shaped structure with two globular domains connected by a flexible linker. Each domain contains two EF-hand motifs, which are helix-loop-helix structures that bind calcium ions.

Error creating thumbnail:

EF-hand motif

EF-hand Motifs

The EF-hand motif is a common structural domain found in calcium-binding proteins. In calmodulin, each EF-hand can bind one calcium ion, allowing the protein to bind a total of four calcium ions. The binding of calcium induces a conformational change in calmodulin, enabling it to interact with various target proteins.

Function

Calmodulin functions as a calcium sensor and signal transducer. Upon binding calcium, calmodulin undergoes a conformational change that allows it to interact with and regulate a variety of target proteins, including kinases, phosphatases, ion channels, and other enzymes.

Calmodulin Binding Sites

Error creating thumbnail:

Calmodulin binding sites

Calmodulin interacts with its target proteins through specific binding sites. These sites are often characterized by a basic amphiphilic helix that fits into the hydrophobic pocket of calmodulin. The interaction is calcium-dependent, meaning that calmodulin must be bound to calcium to effectively bind its targets.

Role in Cellular Processes

Calmodulin plays a critical role in various cellular processes:

• Muscle Contraction: Calmodulin regulates muscle contraction by activating myosin light chain kinase (MLCK), which phosphorylates myosin light chains, facilitating interaction with actin filaments.

Calmodulin bound to MLC Kinase

• Cell Cycle Regulation: Calmodulin is involved in the regulation of the cell cycle by modulating the activity of various kinases and phosphatases.

• Signal Transduction: Calmodulin acts as a key mediator in calcium signal transduction pathways, influencing cellular responses to external stimuli.

Calmodulin in Plants

Error creating thumbnail:

Calmodulin in Sorghum bicolor

In plants, calmodulin is involved in various physiological processes, including growth, development, and response to environmental stimuli. It plays a role in the regulation of plant-specific processes such as stomatal movement and gravitropism.

Calmodulin Domains

N-terminal Domain

Error creating thumbnail:

Calmodulin N-terminal

The N-terminal domain of calmodulin contains two EF-hand motifs and is responsible for binding the first two calcium ions. This domain undergoes a conformational change upon calcium binding, which is crucial for its interaction with target proteins.

C-terminal Domain

Error creating thumbnail:

Calmodulin C-terminal

The C-terminal domain also contains two EF-hand motifs and binds the remaining two calcium ions. The C-terminal domain is important for the stability of the calcium-calmodulin complex and its interaction with target proteins.

Related Pages

• Calcium signaling
• EF-hand
• Signal transduction
• Muscle contraction

   This article is a protein-related stub. You can help WikiMD by expanding it!