游离氨基酸对Аβ多肽异常聚集作用的影响

Effect of Free Amino Acids on the Abnormal Accumulation of Amyloid-β Peptides

阿尔兹海默氏病的主要病因之一,是病人大脑的海马区和皮质区中Аβ多肽异常聚集形成了老年脑斑.本工作通过质谱方法研究游离氨基酸存在下铜离子和Аβ多肽的相互作用,发现由于其侧链极性和强配位能力,天冬氨酸、谷氨酸、亮氨酸、酪氨酸、苏氨酸和组氨酸6种氨基酸能够在较低浓度下明显抑制铜离子和Аβ多肽的结合,由此推测游离氨基酸可能是一种新的与Аβ多肽异常聚集相关的微环境因素.

A major hallmark of Alzheimer’s disease is the senile plaques in cerebral cortex and hippocampus,mainly composed of the abnormal accumulation of amyloid-β（Aβ） peptides.It was suggested that metal ions（such as copper ions） would be a possible key mediating factor for the formation of amyloid deposits by binding to Aβ peptides and triggering the involved aggregation process.Some previous studies have uncovered that the concentration levels of free amino acids（aa） in the brain of AD patients are different from that of normal controls.So we investigated the interactions between copper ions and Aβ peptides in the presence of free amino acids.The effects of sixteen amino acids on the copper-Aβ complexes were examined by electrospray-ionization mass spectrometry（ESI-MS）.Firstly,the mixture solution of Aβ（10-21） peptide（10 μmol/L） and Cu（Gly）2（40 μmol/L） was incubated for 1 h at 37 ℃ in 10 mmol/L ammonium acetate buffer（pH=6.5）.Then stock solution of each amino acid was added yielding Aβ/Cu2＋/aa mixture solution at the final concentration of 1∶4∶x（x= 0,1,2,3,4,5,10） for 200 μL total volume.After 1 h incubation,the samples were analyzed by ESI-MS.Different effects of these amino acids have been observed by comparing the mass spectrum of Aβ/Cu2＋/aa mixture solution with the spectrum of Aβ/Cu2＋mixture solution.Because of their side chain polarity and stronger coordination ability,Asp,Glu,Leu,Tyr,Thr and His can obviously inhibit the combination between copper ions and Aβ peptide at relative low concentrations,and Gln,Asn,Met,Ser and Cys can also inhibit the combination at moderate concentrations.However,Ala,Phe,Ile,Val and Lys can not inhibit at any concentration,and one of them,Lys,can even accelerate their combination.We infer that these amino acids which can inhibit the binding between Аβ peptides and copper ions may have relationships with the formation of the senile plaques and take into consideration that free amino acids may be a new kind of microenvironment factor related with the abnormal accumulation of Aβ peptides.