Proteins, long strings of amino acids, spontaneously fold into intricate shapes that enable them to perform a cell's dazzling variety of functions. To better understand the forces that determine these shapes, scientists have developed a technique for stretching a protein to follow in reverse the path it took when folding.
"The basic idea is to pull the molecule at both ends to stretch it and see what happens," says Ching-Hwa Kiang, a biological physicist at Rice University in Houston.
When a cell builds a protein, it links amino acids that pivot around each other and interlock. These movements are dictated by electrostatic forces between the amino acids and by their tendency to hide their water-repelling sides while leaving their water-lov