Main-Chain Dynamics of Cardiotoxin II from Taiwan Cobra (Naja naja atra) as Studied by Carbon-13 NMR at Natural Abundance: Delineation of the Role of Functionally Important Residues

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• 作者：Chang-Shin Lee ; Thallampuranam Krishnaswamy S. Kumar ; Lu-Yun Lian ; Jya-Wei Cheng ; and Chin Yu
• 刊名：Biochemistry
• 出版年：1998
• 出版时间：January 6, 1998
• 年：1998
• 卷：37
• 期：1
• 页码：155 - 164
• 全文大小：224K
• 年卷期：v.37,no.1(January 6, 1998)
• ISSN：1520-4995

文摘

Cardiotoxin analogue II (CTX II) is an all MG SRC="/images/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-sheet, smallmolecular mass (6.8 kDa), basicprotein possessing a wide array of biological properties. Nearlycomplete assignment of the protonatedcarbon resonances has been achieved by heteronuclear NMR experiments.The study shows that thecorrelation between the carbon-13 chemical shifts and CTX II structureis good in general, but interestingdeviations are also noticed. To characterize the internal dynamicsof CTX II, longitudinal, transverserelaxation rates and heteronuclear ¹³C{¹H}NOEs were measured for mages/gifchars/alpha.gif" BORDER=0>-carbons at natural abundance bytwo-dimensional NMR spectroscopy. Relaxation measurements wereobtained in a 14.1 T spectrometerfor 50 residues, which are evenly spread along the CTX II polypeptidechain. Except for five mages/gifchars/alpha.gif" BORDER=0>-carbons,all data were analyzed from a simple two-parameter spectral densityfunction using the model free approachof Lipari and Szabo. The microdynamical parameters(S², mages/gifchars/tau.gif" BORDER=0 >_e, andR_ex) were calculated with anoverallrotational correlation time (mages/gifchars/tau.gif" BORDER=0 >_m) for the protein of 4.8ns. For most residues, the mages/gifchars/alpha.gif" BORDER=0>-carbons exhibit fast(mages/gifchars/tau.gif" BORDER=0 >_e< 30 ps) restricted libration motions (S² =0.79-0.89). The present study reveals that thefunctionallyimportant residues located at the tips of the three loops are flexible,and the flexibility of residues in thisregion could be important in the binding of cardiotoxins to theirputative "receptors" which are postulatedto be located on the erythrocyte membrane. In addition, theresults obtained in the present study supportthe earlier predictions on the relative role of the lysine residues inthe erythrocyte lytic activity ofcardiotoxins.