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Mechanical Protein Functions

Mechanical Protein Functions

Proteins perform many mechanical functions in a cell. These proteins can be classified into two general categories- proteins that generate mechanical forces and proteins that are subjected to mechanical forces. Proteins providing mechanical support to the structure of the cell, such as keratin, are subjected to mechanical force, whereas proteins involved in cell movement and transport of molecules across cell membranes, such as an ion pump, are examples of generating mechanical force.

Introduction to Actin

Introduction to Actin

Actin is a highly conserved cytoskeletal protein found abundantly in eukaryotic cells. It constitutes 10% weight of the total cellular protein in muscle cells, while in non-muscle cells, it is lower and makes up around 1–5 percent of the total cell protein. Actin found in the unicellular amoebae and complex multicellular animals is around 80% similar, demonstrating their conservation over a billion years of evolution. Actin coding genes are conserved within species and across different species.

Actin and Myosin in Muscle Contraction

Actin and Myosin in Muscle Contraction

Actin and myosin are contractile proteins that form the sarcomere found in skeletal muscle tissues for regulating muscle contraction. Actin, a globular contractile protein, interacts with myosin for muscle contraction. The skeletal tissue appears striped or striated under a microscope due to the repeated arrangement of contractile proteins actin and myosin along the length of myofibrils. Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell causes...

Elastin is Responsible for Tissue Elasticity

Elastin is Responsible for Tissue Elasticity

Elastic fiber contains the protein elastin along with lesser amounts of other proteins and glycoproteins. The main property of elastin is that it will return to its original shape after being stretched or compressed. Elastic fibers are prominent in elastic tissues found in skin and the elastic ligaments of the vertebral column.
Ligaments and tendons are made of dense regular connective tissue, but in ligaments not all fibers are parallel. Dense regular elastic tissue contains elastin fibers and...

Tension Response at Adherens Junctions

Tension Response at Adherens Junctions

The adherens junctions that anchor cells together are multi-protein complexes that dynamically adapt to mechanical stimuli such as tensile forces and shear stress. Mechanosensory proteins in these junctions can sense such mechanical stimuli and undergo a shift in their conformation, resulting in an altered function — a process called mechanotransduction.
α-Catenin as a Mechanosensory Protein
The α-catenin of adherens junctions is an allosteric protein with three VH (vinculin homology) domains...

The Sarcomere

The Sarcomere

A sarcomere is a microscopic segment repeating in a myofibril. The sarcomere fundamentally consists of two main myofilaments: thick filaments called myosin and thin filaments called actin. These filaments interact by sliding past each other in response to stimulus. In addition to myosin and actin, several other proteins, such as tropomyosin, troponin, titin, nebulin, myomesin, α-actinin, and dystrophin, play crucial roles in regulating, structuring, and functioning of the sarcomere.
Each myosin...

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Related Experiment Video

Updated: Jul 27, 2026

In Vitro Assessment of Cardiac Function Using Skinned Cardiomyocytes

In Vitro Assessment of Cardiac Function Using Skinned Cardiomyocytes

Published on: June 22, 2020

Mechanical properties of titin isoforms.

H Granzier¹, M Helmes, O Cazorla

¹Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, USA.

Advances in Experimental Medicine and Biology

|September 15, 2000

Summary

Titin

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Area of Science:

Muscle Physiology
Biophysics
Molecular Biology

Background:

Titin is a giant protein crucial for sarcomere structure and function.
Differential splicing creates titin isoforms with varying lengths in different muscles.
Titin contributes significantly to passive and restoring forces in cardiac and skeletal muscles.

Purpose of the Study:

To investigate the mechanical properties and molecular basis of titin's extensibility in different muscle types.
To model titin's behavior using its known molecular properties and test it against experimental data.
To compare titin isoforms in cardiac myocytes and elucidate their role in passive tension.

Main Methods:

Mechanical testing of skeletal muscle fibers and cardiac myocytes.
Immunoelectron microscopy (IEM) to visualize titin structure and localization.
Development and application of a mechanical model for titin's extensible region.

Main Results:

A model of titin's extensible region as serially linked WLCs adequately predicted behavior in skeletal muscle but overestimated force at long SLs, suggesting Ig domain unfolding.
Cardiac myocytes expressing N2B titin (mouse) showed a steeper passive tension-sarcomere length relation than those expressing N2BA titin (cow).
IEM revealed the N2B sequence as an additional extensibility source in cardiac titin, and the PEVK segment was significantly longer in N2BA (200 nm) than N2B (60 nm).

Conclusions:

Ig domain unfolding may limit titin's force at long sarcomere lengths in skeletal muscle.
The N2B sequence contributes to cardiac titin extensibility.
Longer PEVK segments in N2BA titin isoforms lead to lower passive tensions in cardiac muscle.