Buchet R, Tavitian E, Ristig D, Swoboda R, Stauss U, Gremlich H U, de La Fournière L, Staufenbiel M, Frey P, Lowe D A
Sandoz Research Institute Berne Ltd, Switzerland.
Biochim Biophys Acta. 1996 Jan 17;1315(1):40-6. doi: 10.1016/0925-4439(95)00102-6.
The secondary structures of peptides beta 25-35 (the active toxic fragment) and beta 35-25 (reverse sequence and non-toxic fragment), as well as of the amidated beta (25-35)-NH2 peptide were investigated in aqueous solution and in the solid state by means of Fourier-transformed infrared spectroscopy and circular dichroism spectroscopy. The conformations of the beta 25-35 and beta 35-25 in solid state were identical and contained mostly beta-sheet structures. In solid state the amidated beta (25-35)-NH2 peptide also contained mostly beta-sheet structures. Freshly prepared aqueous solutions of the beta 25-32 (0.5 - 3.8 mM) contained a mixture of beta-sheet and random coil structures. Within 30-60 min incubation at 37 degrees C in water or in phosphate-buffered saline solution (PBS), beta 25-35 was almost fully converted to a beta-sheet structure. Decreasing the temperature from 37 degrees C to 20 degrees C decreased the rate of conversion from random coil to beta-sheet structures, 1-2 h being required for complete conversion. In contrast beta 35-25 in water or in PBS buffer had mostly a random coil structure and remained so for 6 days. The amidated beta(25-35)-NH2 peptide in water (2.7 mM) was also mostly random coil. However, when this peptide (2-2.7 mM) was dissolved in PBS (pH 7.4) or in 140 mM NaCl, a gel was formed and its conformation was mostly beta-sheet. Decreasing the concentration of beta (25-35)-NH2 peptide in 140 mM NaCl aqueous solution from 2 mM to 1 mM or below favored the conversion from beta-sheet structures to random coil structures. The beta 25-35 was toxic to PC12 cells while beta 35-25 was not. The amidated peptide beta (25-35)-NH2 was at least 500-fold less toxic than beta 25-35. Structural differences between these beta peptides in aqueous solutions may explain the difference in their respective toxicities.
通过傅里叶变换红外光谱和圆二色光谱，对β25 - 35（活性毒性片段）、β35 - 25（反向序列且无毒片段）以及酰胺化的β(25 - 35)-NH₂肽在水溶液和固态中的二级结构进行了研究。β25 - 35和β35 - 25在固态时的构象相同，且大多包含β折叠结构。在固态时，酰胺化的β(25 - 35)-NH₂肽也大多包含β折叠结构。新制备的β25 - 32（0.5 - 3.8 mM）水溶液包含β折叠和无规卷曲结构的混合物。在37℃于水或磷酸盐缓冲盐水溶液（PBS）中孵育30 - 60分钟后，β25 - 35几乎完全转变为β折叠结构。将温度从37℃降至20℃会降低从无规卷曲向β折叠结构的转变速率，完全转变需要1 - 2小时。相比之下，β35 - 25在水或PBS缓冲液中大多呈无规卷曲结构，并且6天内保持不变。酰胺化的β(25 - 35)-NH₂肽在水中（2.7 mM）时也大多为无规卷曲结构。然而，当该肽（2 - 2.7 mM）溶解于PBS（pH 7.4）或140 mM NaCl中时，会形成凝胶，其构象大多为β折叠结构。在140 mM NaCl水溶液中，将β(25 - 35)-NH₂肽的浓度从2 mM降至1 mM或更低有利于从β折叠结构向无规卷曲结构的转变。β25 - 35对PC12细胞有毒性而β35 - 25则无毒性。酰胺化肽β(25 - 35)-NH₂的毒性至少比β25 - 35低500倍。这些β肽在水溶液中的结构差异可能解释了它们各自毒性的差异。
