The structural stability of a protein is an important determinant of its proteolytic susceptibility in Escherichia coli.
To investigate the relationship between the degradation rate of a protein in Escherichia coli and its thermal stability in vitro, we constructed a set of variants of the N-terminal domain of lambda repressor with a wide range of melting temperatures. Pulse-chase experiments showed that, within this set, the proteins that are most thermally stable have the longest intracellular half-lives and vice versa. Moreover, second-site mutations which act directly or indirectly to increase the thermodynamic stability of the native N-terminal domain were found to suppress the intracellular degradation of one of the unstable mutants. These data suggest that thermal stability is, indeed, a key determinant of the proteolytic susceptibility of this protein in the cell. It is not the sole determinant, however, as sequences at the extreme C terminus of the N-terminal domain can influence proteolytic sensitivity without affecting the stability of the native structure. We propose that the thermal stability of the N-terminal domain of lambda repressor is an important determinant of its proteolytic sensitivity because degradation proceeds primarily from the unfolded form and that sequence determinants within the unfolded chain influence whether the unfolded protein will be a good substrate for proteolytic enzymes.
Parsell
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Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
Sauer
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D001426:Bacterial Proteins / Q000378:metabolism*; D004252:DNA Mutational Analysis; D004268:DNA-Binding Proteins / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D006358:Hot Temperature; D010447:Peptide Hydrolases / Q000378:metabolism*; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014157:Transcription Factors / Q000378:metabolism*; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D011994:Recombinant Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D014764:Viral Proteins; D054334:Viral Regulatory and Accessory Proteins; C016649:phage repressor proteins; D010447:Peptide Hydrolases