I've been learning about the ClipXP, ClipAP, and Lon proteases. They are proteases from the AAA+ family, which seek out proteins tagged with certain peptide sequences, unfold them, and chop them up.

But what happens when you tag a protease with its own degradation tag? For example, what if you took DNA encoding mf-Lon and added its ssrA tag to the end, and then expressed this sequence in bacteria?

Would this result in any interesting dynamics? Will the protease start trying to degrade itself like an Ouroboros? Will it get stuck trying to do so? Will we observe any interesting dynamics when we incorporate this into a gene circuit?

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    $\begingroup$ The proteases would presumably degrade each other. $\endgroup$
    – canadianer
    Jul 7 '17 at 15:49
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    $\begingroup$ Yeah @canadianer. But I wonder if anything would be different from normal protein degradation. Maybe the protease concentration may have a lower and perhaps more stable steady state? Perhaps because the protease is evolved to degrade other protein, it might be more tightly folded and hence harder to degrade? Might it even get stuck trying to do so? what if two proteases bite each other 69 style? $\endgroup$
    – Cedar
    Jul 7 '17 at 21:29
  • $\begingroup$ You may be dealing with an example of autocatalysis and this may give rise to an S-shaped progress curve (that is, an S-shaped velocity-vs-time plot; not to be confused with an S-shaped velocity-vs-substrate plot). A very good example is trypsinogen/trypsin. See Fig 2 of ISOLATION FROM BEEF PANCREAS OF CRYSTALLINE TRYPSINOGEN ... by Kunitz and Northrop (pdf is free). The kinetics of such a system is well treated by Frost and Pearson, p19 $\endgroup$
    – user338907
    Jul 9 at 23:20

The process of self-degradation of a protease is called autolysis, and the rate of autolysis depends on many factors including temperature, pH, and enzyme concentration.1,2 While most proteases show reduced proteolytic activity with increased autolysis, some proteases demonstrate increased activity after they are self-hydrolyzed. The most notable example is trypsinogen, which, when cleaved initially by enteropeptidase, yields trypsin, an important digestive enzyme. Trypsin can then hydrolyze more trypsinogen molecules in a process known as autocatalysis / autoactivation.3


  1. Chen XL, Shun CY, Zhang YZ, Gao PJ. Rapid monitoring of autolysis process of proteases by capillary electrophoresis. Biotechnol Lett. 2003 Oct;25(20):1763-7.
  2. Khalil ME, Metwalli SM, El-Sebaiy LM. Factors affecting the autolysis rate of crude preparations of proteolytic enzymes from Bouri fish (Mugil cephalus). Food Chem. 1987, 24, 127-135.
  3. Mayer J, Rau B, Schoenberg MH, Beger HG. Mechanism and role of trypsinogen activation in acute pancreatitis. Hepatogastroenterology. 1999 Sep-Oct;46(29):2757-63.

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