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The micro-mechanics of single molecules studied with atomic force microscopy
T E Fisher1, P E Marszalek, A F Oberhauser
1Department of Physiology and Biophysics, Mayo Foundation, 1-117 Medical Sciences Building, Rochester, MN 55905, USA.
The Journal of Physiology
|October 12, 1999
Summary
Atomic force microscopy (AFM) measures piconewton forces and angstrom displacements to reveal the mechanical properties of single biological polymers like extracellular matrix proteins. This technique uncovers how molecular mechanics influence protein function and cellular processes.
Area of Science:
- Biophysics
- Materials Science
- Molecular Biology
Background:
- Mechanical properties of biological polymers are crucial for protein function, particularly for extracellular matrix (ECM) components and adhesion glycoproteins.
- Force-bearing ECM proteins often feature tandem repeats of independently folded domains, essential for structural and mechanical roles.
- Understanding molecular mechanics is key to comprehending cellular processes like exocytosis.
Purpose of the Study:
- To investigate the application of atomic force microscopy (AFM) for studying the mechanical properties of single biological polymers.
- To analyze force-induced conformational changes in proteins and polysaccharides and their functional implications.
- To explore how AFM can elucidate the relationship between protein sequence, mechanical stability, and function.
Main Methods:
- Utilizing atomic force microscopy (AFM) in force-measuring mode to apply piconewton forces and measure angstrom-scale displacements.
- Analyzing force-extension curves of single biological polymers, including amylose and multi-domain proteins.
- Employing site-directed mutagenesis in conjunction with AFM to identify sequence determinants of mechanical stability.
Main Results:
- AFM revealed distinct force-extension behaviors for different biomolecules, such as elasticity transitions in amylose and a "saw tooth" pattern for multi-domain proteins due to sequential domain unfolding.
- Demonstrated the ability to measure rates of protein domain unfolding and refolding through repetitive extension and relaxation cycles.
- Showcased AFM's capacity to link specific amino acid sequences to protein mechanical stability.
Conclusions:
- AFM is a powerful tool for dissecting the mechanical functions of single proteins and biopolymers at the molecular level.
- The technique provides insights into how mechanical forces influence protein conformation and function, relevant to processes like exocytosis.
- AFM enables detailed analysis of protein domain mechanics and the identification of key residues contributing to mechanical stability.