Designed and built entirely in the laboratory, it marks a significant achievement for scientists trying to make the complex biological molecules that assemble and maintain the body.

Proteins are involved in all the biochemical reactions that sustain life and researchers would like to be able to turn them out to order. They also want to design and build completely new shapes not seen in nature.

This would allow them to create a whole range of new drugs and novel materials.

The molecules are made from a chain of chemical units called amino acids which are relatively easy to synthesise in the laboratory.

Specific shape

But scientists have found it extremely difficult to get these chains to fold up into the very specific shapes that make the molecules active and useful.

Nature has little problem achieving this extraordinary feat, but it has taken protein engineering labs around the world many years to create even the simplest of molecules made up of about 25 to 30 amino acids.

The new protein created by researchers at the University of Pennsylvania Medical Center comprises 73 amino acids.

Called alpha-3D, it is a bundle of three counterclockwise-coiling helices whose general shape was inspired by a protein found in the common household bacteria Staphylococcus aureus.

Entirely new proteins

The Penn researchers are now trying to manipulate their molecule to give it some useful function such as the ability to bind to a variety of hormonal receptors.

Natural proteins that do this are expensive to produce and suffer from limited shelf-lives.

News of alpha-3D's creation is reported in the Proceedings of the National Academy of Sciences. Lead author Professor William DeGrado says the research is a big step forward.

"The ability to do this really takes us out of the realm of tinkering with existing proteins to engineering entirely new proteins and polymers.

"We have shown that it is now possible to design a protein with a well-defined three-dimensional structure."