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Limited proteolysis of cytochrome c in trifluoroethanol
A Fontana1, M Zambonin, V De Filippis
1CRIBI Biotechnology Centre, University of Padua, Italy.
Insights
Thermolysin selectively cleaves horse heart cytochrome c in 50% aqueous TFE, indicating protein conformation dictates protease activity. This selective proteolysis offers insights into enzyme-substrate interactions and protein structure.
Area of Science:
- Biochemistry
- Proteomics
- Enzymology
Background:
- Thermolysin is a thermostable metalloprotease with broad substrate specificity.
- Cytochrome c is a crucial protein in cellular respiration.
- Protein conformation significantly influences enzymatic cleavage.
Purpose of the Study:
- To investigate the effect of aqueous trifluoroethanol (TFE) on thermolysin-mediated cleavage of horse heart cytochrome c.
- To understand how protein secondary structure influences protease substrate specificity.
Main Methods:
- Incubation of horse heart cytochrome c with thermolysin in 50% aqueous TFE at neutral pH.
- Analysis of peptide bond cleavage sites using protein sequencing techniques.
- Comparison of proteolysis in the presence and absence of TFE.
Main Results:
- Thermolysin selectively cleaved horse heart cytochrome c at the Gly56-Ile57 bond in 50% aqueous TFE.
- Minor cleavage occurred at Gly45-Phe46 and Met80-Ile81 peptide bonds.
- In buffer alone, thermolysin extensively digested cytochrome c into small peptides.
Conclusions:
- The conformational state of cytochrome c, induced by aqueous TFE, dictates selective proteolysis by thermolysin.
- A highly helical structure in TFE likely hinders protease binding, favoring cleavage at flexible segments.
- Thermolysin's substrate specificity is conformation-dependent, not solely sequence-dependent.
Abstract:
Horse heart cytochrome c is cleaved by thermolysin in 50% aqueous TFE (v/v) at neutral pH (25 degrees C, 24 h) at the Gly56-Ile57 peptide bond of the 104-residue chain of the protein. Additional, but anyway minor, fragmentation at the Gly45-Phe46 and Met80-Ile81 peptide bonds is also observed. On the other hand, in buffer only and in the absence of TFE, cytochrome c is digested by thermolysin to numerous small peptides. Considering the broad substrate specificity of the TFE-resistant thermolysin, clearly the conformational state of the protein substrate dictates the observed selective proteolysis. It is proposed that the highly helical secondary structure acquired by cytochrome c when dissolved in aqueous TFE hampers binding and adaptation of the protein substrate at the active site of the protease and that peptide bond fission occurs at flexible chain segments characterized by a low alpha-helix propensity.