15 NMRによるホヤ体液中のトリプシンインヒビターの溶液構造解析(口頭発表の部)

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Ascidian trypsin inhibitor (ATI) from hemolymph of the solitary ascidian, Halocynthia roretzi, consists of a single polypeptide chain with 55 amino acid residues that shows no extensive homology to other known protease inhibitors. It has four disulfide bridges in a molecule. This is in marked contrast with the better characterized Kunitz-type and Kazal-type inhibitors, most of which contain three disulfide bridges in a molecule. In the present study, we analyzed the solution structure of ATI by means of 2D-NMR and simulated annealing calculations. The resulting structure of ATI is characterized by an α-helical conformation in the sequence, Asn35-His43, and a three-stranded antiparallel β-sheet in the sequence, Leu21-Ile26, Ala29-Arg34 and Glu48-Asn51. The secondary structure and the overall folding of main chain of ATI are similar to those of the third domain of Japanese quail ovomucoid and human pancreatic secretory trypsin inhibitor being a typical Kazal-type inhibitor. These results indicate that ATI is classified as a member of the Kazal-type inhibitor family on the basis of the tertiary structure. On the other hand, ATI has the CSH motif (cystine stabilized α-helical motif), the α-helix structure containing a Cys-X_1-X_2-X_3-Cys sequence stabilized by two disulfide bridges with Cys-X-Cys, which are found in a hormonal peptide (endothelin-1), a honey bee toxin (apamin), a scorpion toxin (charybdotoxin), and so on. It has never been found that Cys at the X_3 position forming the disulfide bridge with other Cys as shown in ATI. These results show that the presence of Cys at the X_3 position does not interfere with the formation of the helix of the CSH motif.
天然有機化合物討論会の論文
1994-09-20

15 NMRによるホヤ体液中のトリプシンインヒビターの溶液構造解析(口頭発表の部)

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