title: NMR solution structure of a Chymotrypsin inhibitor from the Taiwan cobra Naja naja atra.
abstract: The Taiwan cobra (Naja naja atra) chymotrypsin inhibitor (NACI) consists of 57 amino acids and is related to other Kunitz-type inhibitors such as bovine pancreatic trypsin inhibitor (BPTI) and Bungarus fasciatus fraction IX (BF9), another chymotrypsin inhibitor. Here we present the solution structure of NACI. We determined the NMR structure of NACI with a root-mean-square deviation of 0.37 Å for the backbone atoms and 0.73 Å for the heavy atoms on the basis of 1,075 upper distance limits derived from NOE peaks measured in its NOESY spectra. To investigate the structural characteristics of NACI, we compared the three-dimensional structure of NACI with BPTI and BF9. The structure of the NACI protein comprises one 310-helix, one α-helix and one double-stranded antiparallel β-sheet, which is comparable with the secondary structures in BPTI and BF9. The RMSD value between the mean structures is 1.09 Å between NACI and BPTI and 1.27 Å between NACI and BF9. In addition to similar secondary and tertiary structure, NACI might possess similar types of protein conformational fluctuations as reported in BPTI, such as Cys14-Cys38 disulfide bond isomerization, based on line broadening of resonances from residues which are mainly confined to a region around the Cys14-Cys38 disulfide bond.
authors.affiliation: Graduate Institute of Natural Products and Center of Excellence for Environmental Medicine, Kaohsiung Medical University, No.100, Shi-Chuan 1st Road, San-Ming District, Kaohsiung 807, Taiwan. yjlin@kmu.edu.tw
authors.forename: Yi-Jan
authors.initials: YJ
authors.lastname: Lin
authors.forename: Teppei
authors.initials: T
authors.lastname: Ikeya
authors.forename: Peter
authors.initials: P
authors.lastname: Güntert
authors.forename: Long-Sen
authors.initials: LS
authors.lastname: Chang
mesh_terms: D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002918:Chymotrypsin / Q000037:antagonists & inhibitors* / Q000737:chemistry*; D017815:Elapidae; D019906:Nuclear Magnetic Resonance, Biomolecular; D011480:Protease Inhibitors / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013624:Taiwan
chemical_list: D011480:Protease Inhibitors; D002918:Chymotrypsin
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