Solution structure of ascidian trypsin inhibitor determined by nuclear magnetic resonance spectroscopy

Biochemistry. 2002 Aug 27;41(34):10657-64. doi: 10.1021/bi026035o.


The three-dimensional solution structure of ascidian trypsin inhibitor (ATI), a 55 amino acid residue protein with four disulfide bridges, was determined by means of two-dimensional nuclear magnetic resonance (2D NMR) spectroscopy. The resulting structure of ATI was characterized by an alpha-helical conformation in residues 35-42 and a three-stranded antiparallel beta-sheet in residues 22-26, 29-32, and 48-50. The presence of an alpha-helical conformation was predicted from the consensus sequences of the cystine-stabilized alpha-helical (CSH) motif, which is characterized by an alpha-helix structure in the Cys-X(1)-X(2)-X(3)-Cys portion (corresponding to residues 37-41), linking to the Cys-X-Cys portion (corresponding to residues 12-14) folded in an extended structure. The secondary structure and the overall folding of the main chain of ATI were very similar to those of the Kazal-type inhibitors, such as Japanese quail ovomucoid third domain (OMJPQ3) and leech-derived tryptase inhibitor form C (LDTI-C), although ATI does not show extensive sequence homology to these inhibitors except for a few amino acid residues and six of eight half-cystines. On the basis of these findings, we realign the amino acid sequences of representative Kazal-type inhibitors including ATI and discuss the unique structure of ATI with four disulfide bridges.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Disulfides / chemistry
  • Models, Molecular
  • Molecular Sequence Data
  • Nuclear Magnetic Resonance, Biomolecular*
  • Protein Structure, Secondary
  • Sequence Alignment
  • Solutions
  • Structure-Activity Relationship
  • Trypsin Inhibitors / chemistry*
  • Urochordata / chemistry*


  • Disulfides
  • Solutions
  • Trypsin Inhibitors

Associated data

  • PDB/1IW4