Solution structure of ascidian trypsin inhibitor determined by nuclear magnetic resonance spectroscopy.
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.
National Food Research Institute, 2-1-12 Kannondai, Tsukuba, Ibaraki 305-8642, Japan.
Hikaru
H
Hemmi
Takuya
T
Yoshida
Takashi
T
Kumazaki
Nobuaki
N
Nemoto
Jun
J
Hasegawa
Fujio
F
Nishioka
Yoshimasa
Y
Kyogoku
Hideyoshi
H
Yokosawa
Yuji
Y
Kobayashi
D000595:Amino Acid Sequence; D000818:Animals; D004220:Disulfides / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D012996:Solutions; D013329:Structure-Activity Relationship; D014361:Trypsin Inhibitors / Q000737:chemistry*; D014561:Urochordata / Q000737:chemistry*
D004220:Disulfides; D012996:Solutions; D014361:Trypsin Inhibitors