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Drosophila sensory neurons tile the larval body wall, Dr. Chun Han

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Campus Address: GH S-412D, Box 2240
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(415) 476-2521

Courses Taught

David Agard

Structure, Function, and Folding of Proteins, Chromosomes, and Centrosomes

A common assumption in protein folding is that native states of proteins are at a global energy minimum. Recently we have shown that alpha-lytic protease (aLP) shatters this assumption. aLP is an extracellular bacterial serine protease of the chymotrypsin family that is synthesized as a pro-enzyme. Both in vivo and in vitro, we have shown that the pro region (Pro) is absolutely required for correct folding of the protease domain either in cis (pro-enzyme) or in trans (Pro supplied as a separate polypeptide chain). Refolding chemically-denatured aLP in the absence of the pro region results in the formation of a stable molten globule folding intermediate (Int). Addition of pro leads to rapid formation of the native state suggesting that without Pro, folding of Int is blocked by a large kinetic barrier. Recently, we have been able to measure the rates of Int folding (t 1/2 Å 2000 years) and native state unfolding (t1/2 Å 1 year). Remarkably, this demonstrates that the aLP native state is less stable than both the Intermediate and the fully unfolded molecule. aLP stability arises solely from the kinetic barrier that blocks its unfolding and not from thermodynamics. As such, its folding is entirely dependent on the pro region which acts to both catalyze the folding reaction (rate acceleration = 3o109) and to stabilize the native state during folding (Pro is a potent inhibitor of the enzyme, Ki ~10-10M). Free aLP is released through proteolytic degradation of Pro.