A Gentle Tug

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Science  05 Sep 2003:
Vol. 301, Issue 5638, pp. 1291-1293
DOI: 10.1126/science.301.5638.1291d

Designing a protein is such a complicated undertaking in terms of satisfying multiple operating constraints that it seems miraculous that anything works at all. The order of amino acids must allow the spontaneous formation of secondary and tertiary structure during protein synthesis, and the global fold must be flexible enough in enzymes to support catalytic movements and sturdy enough in structural components to resist deformation. Finally, it has to be feasible to tear down these constructs in order to recycle damaged molecules.

Brockwell et al. pull on the N terminus of a lipoyl domain (from a subunit of pyruvate dehdrogenase) while holding onto either the nearby C terminus or the lipoic acid, which is covalently attached to a lysine midway between the termini. Carrion-Vasquez et al. pull on polyubiquitin in which the monomers are linked either by an amide bond between the N and C termini or between an interior lysine and the C terminus. In both cases, yanking on the middle leads to unfolding at much lower forces, by roughly an order of magnitude, than tugging on the two ends. Perhaps this explains how proteins can be tough, yet have a sensitive side. — GJC

Nature Struct. Biol. 10.1038/nsb968; 10.1038/nsb965 (2003).

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