Protein Engineering, Vol 11, 1211-1217, Copyright © 1998 by Oxford University Press
J Van der Schueren, J Robben and G Volckaert
Folding of chloramphenicol acetyltransferase (CAT) in Escherichia coli is
hampered by deletion of the carboxy-terminal tail including the last
residue of the carboxy-terminal alpha-helix. Such truncated CAT
polypeptides quantitatively aggregate into cytoplasmic inclusion bodies,
which results in absence of a chloramphenicol-resistant phenotype for the
producing host. In this paper, a genetic approach is presented to examine
this aggregation process in more detail. Random mutagenesis of inactive CAT
followed by direct phenotypic selection for revertants with restored
chloramphenicol resistance was used to isolate second-site suppressors of
inactive truncation mutants of CAT. Two random mutagenesis procedures,
independently of each other, yielded a unique substitution of Phe for Leu
at amino acid position 145. This second-site mutation does not drastically
affect the proteins' stability under normal growth conditions of E. coli.
Hence, the introduction of Phe at amino acid position 145 improves the
ability of the protein to fold into a soluble, enzymatically active
conformation. The conservative character of the Leu145Phe replacement
indicates that limited changes at crucial positions can have important
effects on protein folding in vivo.
ARTICLES
Misfolding of chloramphenicol acetyltransferase due to carboxy-terminal truncation can be corrected by second-site mutations
Laboratory of Gene Technology, Katholieke Universiteit Leuven, Belgium. jan.vanderschueren@agr.kuleuven.ac.be
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