Proteinase inhibitors from desert locust, Schistocerca gregaria: Engineering of both P1 and P1' residues converts a potent chymotrypsin inhibitor to a potent trypsin inhibitor

Zulfiquar Malik, Sumaira Amir, Gábor Pál, Zsuzsa Buzás, Éva Várallyay, József Antal, Zoltán Szilágyi, Károly Vékey, Bence Asbóth, András Patthy, László Gráf

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Two peptides, SGCI and SGTI, that inhibited chymotrypsin and trypsin, respectively, were isolated from the haemolymph of Schistocerca gregaria. Their primary structures were found to be identical with SGP-2 and SGP-1, two of a series of peptides isolated from ovaries of the same species (A. Hamdaoui et al., FEBS Lett. 422 (1998) 74-78). All these peptides are composed of 35-36 amino acid residues and contain three homologous disulfide bridges. The residues imparting specificity to SGCI and SGTI were identified as Leu-30 and Arg-29, respectively. The peptides were synthesised by solid- phase peptide synthesis, and the synthetic ones displayed the same inhibition as the natural forms: SGCI is a strong inhibitor of chymotrypsin (K(i)=6.2 x 10-12 M), and SGTI is a rather weak inhibitor of trypsin (K(i)=2.1 x 10- 7 M). The replacement of P1 then P1' residues of SGCI with trypsin- specific residues increased affinity towards trypsin 3600- and 1100-fold, respectively, thus SGCI was converted to a strong trypsin inhibitor (K(i)=5.0 x 10-12 M) that retained some inhibitory affinity towards chymotrypsin (K(i)=3.5 x 10-8 M). The documented role of both P1 and P1' highlights the importance of S1'P1' interactions in enzyme-inhibitor complexes.

Original languageEnglish (US)
Pages (from-to)143-150
Number of pages8
JournalBiochimica et Biophysica Acta - Protein Structure and Molecular Enzymology
Issue number1
StatePublished - Sep 14 1999
Externally publishedYes



  • Chymotrypsin
  • Insect peptide
  • Protein protease inhibitor
  • Schistocerca gregaria
  • Subsite specificity

ASJC Scopus subject areas

  • Structural Biology
  • Biophysics
  • Biochemistry
  • Molecular Biology

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