Protein elasticity measurement method developed

A procedure for measuring the elasticity of proteins has been developed by a research team at the Tokyo Institute of Technology. The method is expected to play a role in the analysis of protein function and also for the development of micromachines using biological molecules.

In the technique, a long, thin string-like protein is attached by one end to a silicon substrate and then pulled from the other end by the probe tip of an atomic force microscope (AFM), which has the ability to detect small forces.

The 'hardness' of the protein can be derived from the force applied by the AFM probe tip and the distance the protein stretches.

The two ends of a string-like protein have different biochemical properties. At one end, the N-terminal, is an amino base, and at the other end the C-terminal is a carboxyl base. In the new procedure, the N-terminal is attached to the silicon substrate and the C-terminal is attached to the AFM probe tip.

In experiments with the protein carbonic anhydrase, an enzyme made by red blood cells that helps in the transport of carbon dioxide, the first measurement showed that a force of 1.5nN is required to stretch the protein 90nm. After the protein was hardened with a chemical agent, a force of 2nN was required to stretch it just 30nm.

These tests demonstrate that the system can be used to measure the elasticity of proteins. Since the hardness of a protein is related to its function as an enzyme, the new measuring technique could be utilized in proteomic studies to analyse the functions of proteins.

It might also find use in the development of molecular-based motors and devices in the emerging field of nanotechnology.