- 作者: 林婉真; 朱善德; 陳義雄
- 作者服務機構: 國立臺灣大學生物化學研究所; 中央研究院生物化學研究所
- 中文摘要:
β一雨傘節蛋白(β-bungarotoxin)由兩個蛋白分子鏈(A鏈和B鏈)以雙硫鍵連接而成,其中A蛋白鏈和磷酯酸水解
?的胺基酸排列次序相似。由分光光譜之分析,發現β-雨傘節蛋白分子中含有少量典型的α立體結構。進一步研究而
知有機溶劑不會造成β-雨傘節蛋白的變性。例如在乙二醇(1, 2-ethanediol)和水的混合液中(4:1),其立體結構維特
與水溶液之結構相似。但於6.0 M?酸胍(guanidine hydrochloride)中,則此蛋白變性(denaturation):蛋白中之規則結
構(ordered structure)變成不規則結構(unordered structure)。利用CNBr修飾法將A蛋白鏈近胺基末端的8個胺基
酸切除後,並不影響此蛋白的分子結構,但?使β-雨傘節蛋白失去其毒性。由helix-coil transition之比較研究而推測
,A和B蛋白分子鏈必需交互作用,才能維持β-雨傘節蛋白有效之立體結構(active conformation)。
n - 英文摘要: β-Bungarotoxin, which consists of two polypeptide chains (A- and B-chain), in the venom of Formo-san banded krait is stable in 7.5 M urea but can be denatured in 6.0 M guanidine hydrochloride. Its con-formation remains virtually the same in solvents of lower polarity than water such as a mixture of 1,2-ethanediol-water (4:1 by volume). The circular dichroism spectrum in water shows a double minima at222 and 209 nm, which is characteristic of the helical structure. The ellipticities at these two wavelengthsindicate that the helical content of this toxin is not high. Comparing how guanidine hydrochloride effectsthe helix-coil transition of the toxin with that of phospholipase A 's which are structurally homologous toA-chain implicates that the two polypeptide chains should be coexisted and interacted with each other inorder to maintain the active conformation of β-bungarotoxin. Removal of eight amino acid residues fromthe N-terminus of the A-chain by action of CNBr on β-bungarotoxin does not disrupt the polypeptidefolding but abolishes the neurotoxicitv.
- 中文關鍵字: circular dichrosim; presynaptical toxin; protein conformation
- 英文關鍵字: --