Rustem I. Litvinov studies the molecular mechanics of fibrin, the protein network formed during coagulation. A 2005 study led by Litvinov used optical tweezers to measure forces between individual interacting molecules. It examined fibrin knob-hole interactions, in which an exposed part of one molecule fits into a complementary binding pocket on another.[ref]
The apparatus repeatedly brought a protein-coated bead into contact with a coated surface, then pulled the partners apart. The force rose while they remained attached and dropped when attachment ruptured. Removing a complementary binding part or adding a competing peptide suppressed the strong interactions. These controls helped distinguish specific molecular recognition from nonspecific adhesion. Forces around 125–130 piconewtons characterized the strong interactions under the experiment's pulling conditions. Such rupture measurements connect molecular assembly to mechanics, but the numerical rupture force is not a universal constant independent of how a bond is loaded.[ref]
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