J Biol Chem, Vol. 274, Issue 32, 22217-22224, August 6, 1999
Single Amino Acid Substitutions Globally Suppress the Folding
Defects of Temperature-sensitive Folding Mutants of Phage P22 Coat
Protein
Lili A.
Aramli and
Carolyn M.
Teschke
From the Department of Molecular and Cell Biology, University of
Connecticut, Storrs, Connecticut 06269-3125
The amino acid sequence of a polypeptide defines
both the folding pathway and the final three-dimensional structure of a
protein. Eighteen amino acid substitutions have been identified in
bacteriophage P22 coat protein that are defective in folding and cause
their folding intermediates to be substrates for GroEL and GroES. These temperature-sensitive folding (tsf) substitutions identify amino acids
that are critical for directing the folding of coat protein. Additional
amino acid residues that are critical to the folding process of P22
coat protein were identified by isolating second site suppressors of
the tsf coat proteins. Suppressor substitutions isolated from the phage
carrying the tsf coat protein substitutions included global
suppressors, which are substitutions capable of alleviating the folding
defects of numerous tsf coat protein mutants. In addition, potential
global and site-specific suppressors were isolated, as well as a group
of same site amino acid substitutions that had a less severe phenotype
than the tsf parent. The global suppressors were located at positions
163, 166, and 170 in the coat protein sequence and were 8-190 amino
acid residues away from the tsf parent. Although the folding of coat
proteins with tsf amino acid substitutions was improved by the global
suppressor substitutions, GroEL remained necessary for folding.
Therefore, we believe that the global suppressor sites identify a
region that is critical to the folding of coat protein.
Copyright © 1999 by The American Society for Biochemistry and Molecular Biology, Inc.