[excerpt] Although they are much weaker than the preeminent "covalent" chemical bonds that bind atoms in biological molecules, hydrogen bonds are known to occur at key points along the central "backbone" structures of all folded proteins. The hydrogen bonds are created by attractions between adjacent hydrogen and oxygen atoms that are sandwiched into the molecular framework.
How big a role hydrogen bonds actually play in protein folding has been a controversial scientific question, according to Duke associate chemistry professor Michael Fitzgerald. "There's been an ongoing debate about the exact role of those hydrogen bonds," he said in an interview. "Are they really super-important, or are they really negligible?"
Fitzgerald, his graduate student Min Wang and his former graduate student Thomas Wales helped address that question in an effort that took years of work.
One by one, they slightly "mutated" the normal arrangement of atoms in proteins to effectively delete hydrogen bonds at five analogous positions along the structural "backbones" of two different protein molecules that fold in the same pattern. Then they analyzed how each deletion affected the stability of the protein. "Stability" means how low energy, or "relaxed," the protein was.
"We deleted each hydrogen bond and then measured how relaxed the protein was afterwards," Fitzgerald said. "It turns out we destabilized the structure in each case. So the relaxed state was not so relaxed any more. The proteins were more stable with those hydrogen bonds.
"Those bonds seemed to clearly play a role in protein folding. And what we were able to uncover in this work is that this role may be highly conserved in a protein fold."
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