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.
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 beta-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.
Chen
Ting-Shou
TS
Institute of Bioinformatics and Structural Biology, National Tsing Hua University, Hsinchu 300, Taiwan.
Chung
Fong-Yu
FY
Tjong
Siu-Cin
SC
Goh
King-Siang
KS
Huang
Wei-Ning
WN
Chien
Kun-Yi
KY
Wu
Po-Long
PL
Lin
Hua-Ching
HC
Chen
Chun-Jung
CJ
Wu
Wen-Guey
WG
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002942:Circular Dichroism; D004179:Cobra Cardiotoxin Proteins / Q000737:chemistry* / Q000145:classification* / Q000302:isolation & purification; D003460:Crystallization; D018360:Crystallography, X-Ray; D004546:Elapid Venoms / Q000737:chemistry* / Q000145:classification* / Q000302:isolation & purification; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010718:Phosphatidylserines / Q000737:chemistry; D011392:Proline / Q000737:chemistry*; D011485:Protein Binding; D011487:Protein Conformation; D012996:Solutions; D013624:Taiwan
D004179:Cobra Cardiotoxin Proteins; D004546:Elapid Venoms; D010718:Phosphatidylserines; D012996:Solutions; C042511:1,2-dioleoylphosphatidylserine; D011392:Proline