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Selective oxidation of methionine residues in Kunitz-type protease inhibitors

A Concetti1, M Angeletti, E Fioretti

  • 1Dipartimento di Biologia Cellulare, Università di Camerino.

Biological Chemistry Hoppe-Seyler
|July 1, 1989
PubMed

Insights

Oxidizing bovine pancreatic trypsin inhibitor (BPTI) and spleen inhibitor II (SI II) with chloramine T differently impacts their function. BPTI activity remains unchanged, while SI II shows reduced protease affinity due to methionine oxidation.

Area of Science:

  • Biochemistry
  • Protease Inhibitor Research
  • Protein Oxidation Studies

Background:

  • Bovine pancreatic trypsin inhibitor (BPTI), also known as aprotinin, is a mini-protein with 58 amino acids and one methionine residue.
  • Spleen inhibitor II (SI II) is an isoform of BPTI, featuring two methionine residues.
  • Methionine residues in proteins are susceptible to oxidation, potentially altering protein function.

Purpose of the Study:

  • To investigate the effects of selective oxidation on the functional properties of BPTI and SI II.
  • To compare the impact of methionyl sulfoxide formation on the antiproteolytic activities of BPTI and SI II.
  • To elucidate the role of specific methionine residues in protease binding and inhibition.

Main Methods:

  • Selective oxidation of BPTI and SI II using chloramine T under mild conditions.
  • Characterization of the resulting methionyl sulfoxide derivatives.
  • Assays to evaluate the antiproteolytic activity and protease binding affinity of native and oxidized inhibitors.

Main Results:

  • Oxidation of BPTI to its methionyl sulfoxide derivative did not alter its antiproteolytic activity against trypsin, chymotrypsin, kallikrein, and elastase.
  • Oxidation of SI II resulted in a decreased affinity for chymotrypsin and elastase compared to the native protein.
  • The observed functional changes in SI II were attributed to the oxidation of methionine at position 18 (Met18), located in the protease contact site.

Conclusions:

  • The functional consequences of methionine oxidation in Kunitz-type inhibitors vary depending on the inhibitor's structure and the location of methionine residues.
  • Met18 in SI II plays a crucial role in maintaining high affinity for chymotrypsin and elastase, as its oxidation significantly impairs binding.
  • This study highlights the differential impact of protein oxidation on the functional integrity of structurally related protease inhibitors.

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