The key difference between troponin and calmodulin is that troponin is a complex of three proteins found in the cardiac and skeletal muscles while calmodulin is a small dumbbell shaped-protein found in the cytoplasm of all eukaryotic cells.

Troponin and calmodulin are two proteins. Troponin is a complex of three proteins, while calmodulin is a small protein made up of two globular domains connected by a central alpha helix. Troponin is important in the regulation of heart and skeletal muscle contraction. In contrast, calmodulin regulates many cellular processes.

CONTENTS

1. Overview and Key Difference
2. What is Troponin 
3. What is Calmodulin
4. Similarities Between Troponin and Calmodulin
5. Side by Side Comparison – Troponin vs Calmodulin in Tabular Form
6. Summary

What is Troponin?

Troponin is a complex of three regulatory proteins found in the cardiac and skeletal muscles. The three different proteins are troponin T, troponin C and troponin I. Troponin proteins help to regulate the contractions of the heart and skeletal muscles. Troponin C is similar to calmodulin both in amino acid sequence and in three-dimensional structure. Similar to calmodulin, troponin C has calcium-binding sites.

Figure 01: Troponin C

Generally, troponin is present in very small amounts in our blood and is undetectable. The normal value is below 0.04 ng/ml. However, if there is a slight but detectable increase in the troponin level, it indicates a risk of heart damage. This is because when there is a damage in heart muscles, it releases troponin into the bloodstream. Therefore, a significantly raised level of troponin is a strong indication of a heart injury. The troponin level above 0.04 ng/ml indicates a probable heart attack. Therefore, doctors carry out a troponin test to assess whether there is damage in the heart. Troponin test is a simple blood test, and it measures troponin T or troponin I proteins in the blood.

What is Calmodulin?

Calmodulin is a small dumbbell-shaped protein which is present in the cytoplasm of all eukaryotic cells. Calmodulin is a highly conserved protein. It is ubiquitous in all eukaryotic cells and is best known for its ability to activate CaM-dependent kinases in a variety of cells.  It is made up of two globular domains connected by a central alpha helix. Each domain has three alpha-helices and two calcium-binding EF hands. The size of the protein is 16.7kDa.

Figure 02: Calmodulin

The major function of calmodulin is to mediate Ca2+ dependent signalling. Therefore, it mediates the control of a large number of enzymes, ion channels, and other proteins by calcium. Moreover, it regulates many other cellular processes.

What are the Similarities Between Troponin and Calmodulin?

• Troponin and calmodulin are proteins.
• They fulfil important functions in our body.
• Calmodulin is similar to troponin C.

What is the Difference Between Troponin and Calmodulin?

Troponin is a protein present in cardiac and skeletal muscles, while calmodulin is a protein present in the cytoplasm of all eukaryotic cells. So, this is the key difference between troponin and calmodulin. Structurally, troponin is a complex of three proteins, while calmodulin is composed of two globular domains connected by a central alpha-helix.

Moreover, another significant difference between troponin and calmodulin is their function; troponin regulates the contractions of the heart and skeletal muscles while calmodulin mediates Ca2+ -dependent signalling.

Below infographic summarizes the difference between troponin and calmodulin.

Summary – Troponin vs Calmodulin

Troponin is a protein found in skeletal and heart muscle fibres. It regulates muscular contraction. Troponin level in our bloodstream is undetectable. When the heart muscles are damaged, they release troponin into the blood so, high troponin levels indicate probable heart injuries. In contrast, calmodulin is a small dumbbell-shaped protein present in all eukaryotic cells. It mediates calcium dependant signalling. Thus, this summarizes the difference between troponin and calmodulin.

Reference:

1. “Normal Troponin Levels: What High Levels Mean, Plus Causes”. Medicalnewstoday.Com, 2020, Available here.
2. “Calmodulin”. Collab.Its.Virginia.Edu, 2020, Available here.

Image Courtesy:

1. “PDB 1ncy EBI” By Jawahar Swaminathan and MSD staff at the European Bioinformatics Institute – (Public Domain) via Commons Wikimedia
2. “Calmodulin Binding sites” By PDB – from the Molecule of the Month feature by David Goodsell at the RCSB Protein Data Bank. (CC BY-SA 4.0) via Commons Wikimedia

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