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| The EMBO Journal
(1997) 16, 54–58, doi:10.1093/emboj/16.1.54 |
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| Cooperation of enzymatic and chaperone functions of trigger factor in the catalysis of protein folding |
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| Christian Scholz1, Gerlind Stoller2, Toralf Zarnt2, Gunter Fischer2 and Franz X. Schmid1 |
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1 Laboratorium fu¨r Biochemie, Universita¨t Bayreuth, D-95440 Bayreuth, Germany 2 Max-Planck-Gesellschaft, Arbeitsgruppe 'Enzymologie der Peptidbindung', Kurt-Mothes-Strasse 3, D-06120 Halle/Saale, Germany Received 22 July 1996; Revised 16 September 1996. |
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| Abstract |
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The trigger factor of Escherichia coli is a prolyl isomerase and accelerates proline-limited steps in protein folding with a very high efficiency. It associates with nascent polypeptide chains at the ribosome and is thought to catalyse the folding of newly synthesized proteins. In its enzymatic mechanism the trigger factor follows the Michaelis–Menten equation. The unusually high folding activity of the trigger factor originates from its tight binding to the folding protein substrate, as reflected in the low Km value of 0.7  M. In contrast, the catalytic constant kcat is small and shows a value of 1.3 s-1 at 15°C. An unfolded protein inhibits the trigger factor in a competitive fashion. The isolated catalytic domain of the trigger factor retains the full prolyl isomerase activity towards short peptides, but in a protein folding reaction its activity is 800-fold reduced and no longer inhibited by an unfolded protein. Unlike the prolyl isomerase site, the polypeptide binding site obviously extends beyond the FKBP domain. Together, this suggests that the good substrate binding, i.e. the chaperone property, of the intact trigger factor is responsible for its high efficiency as a catalyst of proline-limited protein folding. |
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| Keywords: chaperone, enzyme kinetics, prolyl isomerase, protein folding, trigger factor |
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