Difference Between Calmodulin and Troponin C

The key difference between calmodulin and troponin C is that calmodulin can bind with only calcium ions whereas troponin C is able to bind with both calcium and magnesium ions.

Calmodulin and troponin C are proteins in eukaryotes. Both act as calcium-binding messenger proteins. More importantly, calmodulin can bind with only calcium while troponin C can bind with both calcium and magnesium.

CONTENTS

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

What is Calmodulin?

Calmodulin refers to the calcium modulated protein. It can be found in all eukaryotic cells. It can also act as a multifunctional intermediate calcium-binding protein. This protein acts as an intercellular target for secondary messenger calcium ions. Moreover, for the activation of the calmodulin protein, the binding of the secondary messenger calcium ions is neccessary. Once it is activated, it can act as a part of the calcium signal transduction pathway.

When considering the structure of this protein, it is a small protein having about 148 amino acids. It has approximately two globular regions. Each of these regions contains two EF-hand motifs which can bind with the calcium ions. There is a flexible linker region between these globular regions. Therefore, the calmodulin molecule has four sites for calcium ion binding.

Moreover, the calmodulin protein can bind with a variety of target molecules. Therefore, it is very important to have flexibility in this protein. The generic shape of the non-polar grooves in the binding sites allows it to bind with a variety of targets.

What is Troponin C?

Troponin C is a protein that exists as a part of the troponin complex. There are four EF motifs in the troponin C molecule for the bonding of calcium ions. Moreover, this protein exists as a component in thin filaments in combination with actin and tropomyosin.

A troponin C molecule contains two lobes: N lobe and C lobe. The C lobe is important as a structural component and helps in binding to the N domain of the troponin I. Also, the C lobe is able to bind with either calcium ions or magnesium ions. However, the N lobe binds only with calcium ions. It is the regulatory lobe of this protein and after biding with a calcium ion, it can bind with the C domain of the troponin I.

There are two subtypes of troponin C as slow troponin and fast troponin. Moreover, there are a number of mutations for this protein as well. These mutations can cause structural alterations of troponin C and in the binding of calcium and magnesium ions as well. These mutations can cause abnormalities in muscle contractions.

What is the Difference Between Calmodulin and Troponin C?

Calmodulin and troponin C are proteins in eukaryotes. Both these proteins have four EF-hand motifs that can bind with calcium (and/or magnesium) ions. However, the key difference between calmodulin and troponin C is that calmodulin can bind with only calcium ions whereas troponin C is able to bind with both calcium and magnesium ions.

Below infographic summarizes the difference between calmodulin and troponin C .

Summary – Calmodulin vs Troponin C

Calmodulin and troponin C are proteins in eukaryotes. The key difference between calmodulin and troponin C is that calmodulin can bind with only calcium ions whereas troponin C is able to bind with both calcium and magnesium ions.

Reference:

1. Issa, Ziad F., et al. “Ventricular Arrhythmias in Inherited Channelopathies.” Clinical Arrhythmology and Electrophysiology: A Companion to Braunwalds Heart Disease, 2012, pp. 645–684., doi:10.1016/b978-1-4557-1274-8.00031-2.

Image Courtesy:

1. “Calmodulin” By User Magnus Manske on en.wikipedia – Originally from en.wikipedia: 13:27, 22 June 2004 Magnus Manske 564×519 (34,897 bytes) ({{PD}}) (Public Domain) via Commons Wikimedia
2. “Troponino” By Arcadian – Troponino.jpg via Commons Wikimedia