Terlau H, Heinemann S H, Stühmer W, Pusch M, Conti F, Imoto K, Numa S
Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany.
FEBS Lett. 1991 Nov 18;293(1-2):93-6. doi: 10.1016/0014-5793(91)81159-6.
The SS2 and adjacent regions of the 4 internal repeats of sodium channel II were subjected to single mutations involving, mainly, charged amino acid residues. These sodium channel mutants, expressed in Xenopus oocytes by microinjection of cDNA-derived mRNAs, were tested for sensitivity to tetrodotoxin and saxitoxin and for single-channel conductance. The results obtained show that mutations involving 2 clusters of predominantly negatively charged residues, located at equivalent positions in the SS2 segment of the 4 repeats, strongly reduce toxin sensitivity, whereas mutations of adjacent residues exert much smaller or no effects. This suggests that the 2 clusters of residues, probably forming ring structures, take part in the extracellular mouth and/or the pore wall of the sodium channel. This view is further supported by our finding that all mutations reducing net negative charge in these amino acid clusters cause a marked decrease in single-channel conductance.
对钠通道II的4个内部重复序列的SS2及其相邻区域进行了单突变，主要涉及带电荷的氨基酸残基。通过显微注射cDNA衍生的mRNA在非洲爪蟾卵母细胞中表达这些钠通道突变体，并测试它们对河豚毒素和石房蛤毒素的敏感性以及单通道电导。所得结果表明，涉及4个重复序列的SS2片段中同等位置的2个主要带负电荷残基簇的突变，会强烈降低毒素敏感性，而相邻残基的突变产生的影响要小得多或没有影响。这表明，这2个残基簇可能形成环状结构，参与钠通道的细胞外口和/或孔壁。我们的发现进一步支持了这一观点，即这些氨基酸簇中所有降低净负电荷的突变都会导致单通道电导显著降低。
