Structural Difference between Group I and Group II Cobra Cardiotoxins: X-ray, NMR, and CD Analysis of the Effect of cis-Proline Conformation on Three-Fingered Toxins

• Published in: Biochemistry (Easton) 2005-05, Vol.44 (20), p.7414-7426
• Main Authors: Chen, Ting-Shou, Chung, Fong-Yu, Tjong, Siu-Cin, Goh, King-Siang, Huang, Wei-Ning, Chien, Kun-Yi, Wu, Po-Long, Lin, Hua-Ching, Chen, Chun-Jung, Wu, Wen-guey
• Format: Article
• Language: English
• Subjects: Amino Acid Motifs; Amino Acid Sequence; Animals; Circular Dichroism; Cobra Cardiotoxin Proteins - chemistry; Cobra Cardiotoxin Proteins - classification; Cobra Cardiotoxin Proteins - isolation & purification; Crystallization; Crystallography, X-Ray; Elapid Venoms - chemistry; Elapid Venoms - classification; Elapid Venoms - isolation & purification; Models, Molecular; Molecular Sequence Data; Nuclear Magnetic Resonance, Biomolecular; Phosphatidylserines - chemistry; Proline - chemistry; Protein Binding; Protein Conformation; Solutions; Taiwan
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi050172e

Natural homologues of cobra cardiotoxins (CTXs) were classified into two structural subclasses of group I and II based on the amino acid sequence and circular dichroism analysis, but the exact differences in their three-dimensional structures and biological significance remain elusive. We show by circular dichroism, NMR spectroscopic, and X-ray crystallographic analyses of a newly purified group I CTX A6 from eastern Taiwan cobra (Naja atra) venoms that its loop I conformation adopts a type VIa turn with a cis peptide bond located between two proline residues of PPxY. A similar “banana-twisted” conformation can be observed in other group I CTXs and also in cyclolinopeptide A and its analogues. By binding to the membrane environment, group I CTX undergoes a conformational change to adopt a more extended hydrophobic domain with β-sheet twisting closer to the one adopted by group II CTX. This result resolves a discrepancy in the CTX structural difference reported previously between solution as well as crystal state and shows that, in addition to the hydrophobicity, the exact loop I conformation also plays an important role in CTX−membrane interaction. Potential protein targets of group I CTXs after cell internalization are also discussed on the basis of the determined loop I conformation.