King, J., Haase-Pettingell, C., Gordon, C., Sather, S. and Mitraki, A. (1993) In Protein Folding: In Vivo and In Vitro (ed. J. Cleland) ACS Symposium Series 526, American Chemical Society, Washington, D.C., pp. 24-37

"Amino Acid Sequence Determinants of Polypeptide Chain Folding and Inclusion Body Formation"

Newly synthesized polypeptide chains within cells pass through a series of partially folded intermediates in reaching their native state. Association of these intermediates into the aggregated inclusion body state often competes with productive folding into the native state, in both prokaryotic and eukaryotic cells. For the thermostable tailspike of phage P22, a thermolabile early folding intermediate switches from the productive pathway to the inclusion body pathway with increasing temperature. Two classes of amino acid substitutions influence the behavior of these intracellular folding intermediates. Temperature sensitive folding (tsf) mutations destabilize the critical intermediates in the chain folding pathway at elevated temperatures, resulting in their polymerization into the aggregated inclusion body state, a kinetic trap for the chains. Global suppressors of the tsf mutations inhibit chain entry into the inclusion body pathway. Neither the tsf nor global suppressor substitutions alter the activity or stability of the native state once correctly folded. For tsf mutations in the major coat protein, overexpression of the GroEL/S chaperonin efficiently suppresses the tsf folding defects. The isolation of global suppressor mutations, and overexpression of chaperonins, may be general strategies for solving problems of protein expression and protein recovery in biotechnology.

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