Selective gas-phase cleavage at the peptide bond terminal to aspartic acid in fixed-charge derivatives of asp-containing peptides
Selective gas-phase cleavage at the peptide bond terminal to aspartic acid in fixed-charge derivatives of asp-containing peptides
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DOI：
10.1021/ac000555c
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发表时间：
2000-12-01
影响因子：
7.4
通讯作者：
Wysocki, VH
中科院分区：
文献类型：
--
作者：
Gu, CG;Tsaprailis, G;Wysocki, VH
本研究聚焦于对质子化肽中天冬氨酸残基（Asp）选择性气相裂解的分子水平解释。通过固相合成，将Aφ3P + CH2C(=O)( - )基团（φ = 2,4,6 - 三甲氧基苯基）连接到所选肽LDIFSDF和LDIFSDFR的N端氮上，以“模拟”质子化精氨酸（Arg）残基紧密保持的电荷。对固定电荷肽衍生物的电喷雾产生的离子，在四极杆离子阱仪器中进行了碰撞诱导解离，在双四极杆仪器中进行了表面诱导解离。对于仅由固定电荷提供电荷的离子，或对于具有固定电荷以及一个Arg和一个外加质子的离子，观察到在Asp - Xxx处的选择性裂解。这支持了先前提出的一种机制，该机制表明当质子化肽中的电离质子被Arg强烈结合时，由Asp残基的酸性氢引发的在Asp - Xxx处的裂解变得显著。很明显，固定电荷确实起到了质子化Arg的“模拟”作用，并且质子化的Arg侧链不需要与Asp相互作用来诱导在Asp - Xxx处的裂解。当质子数量超过含有Arg和Asp的肽中Arg的数量时，会发生非选择性裂解。肽的裂解效率与这些非选择性裂解由可移动质子促进的观点一致。具有固定电荷和一个外加质子的肽[φ3P + CH2C(=O) - LDIFSDF + H](2 + )比具有固定电荷、一个Arg和一个外加质子的相应肽[φ3P + CH2C(=O) - LDIFSDFR + H](2 + )裂解效率高得多；这两种肽都比具有固定电荷且无外加质子的肽φ3P + CH2C(=O) - LDIFSDF裂解效率高。对来自φ3P + CH2C(=O) - LDIFSDF及其H/D交换衍生物φ3P + CH2C(=O) - LDIFSDF - d(11)在Asp - Xxx处形成的b(n)离子进行的MS/MS/MS（即MS3）实验结果与在Asp - Xxx处形成的b(n)离子具有琥珀酸酐环状结构一致。还对φ3P + CH2C(=O) - AAAA（一种仅在酰胺氮和C端含有活性氢的肽衍生物）及其活性H/D交换产物φ3P + CH2C(=O) - AAAA - d(5)进行了MS/MS实验。结果表明，在形成环状电荷远程b离子时，原本位于酰胺氮上的氢被转移走。
This study focuses on the molecular level interpretation of the selective gas-phase cleavage at aspartic acid residues (Asp) in protonated peptides, A phi 3P+CH2C(=O)(-) group (phi = 2,4,6-trimethoxyphenyl) is attached to the N-terminal nitrogen of the selected peptides LDIFSDF and LDIFSDFR, via solid-phase synthesis, to "mimic" the tightly held charge of a protonated arginine (Arg) residue. Collision-induced dissociation in a quadrupole ion trap instrument and surface-induced dissociation in a dual quadrupole instrument were performed for electrospray-generated ions of the fixed-charge peptide derivatives. Selective cleavages at Asp-Xxx are observed for those ions with charge provided only by the fixed charge or for those with a fixed charge and one Arg plus one added proton. This supports a previously proposed mechanism which suggests that the cleavages at Asp-Xxx, initiated by the acidic hydrogen of the Asp residue, become significant when ionizing protons are strongly bound by Arg in the protonated peptides, It is clear that the fixed charge is indeed serving as a "mimic" of protonated Arg and that a protonated Arg side chain is not required to interact with the Asp to induce cleavage at Asp-Xxx, When the number of protons exceeds the number of Arg in a peptide containing Arg and Asp, nonselective cleavages occur. The fragmentation efficiency of the peptides is consistent with the idea that these nonselective cleavages are promoted by a mobile proton. The peptide with a fixed charge and one added proton, [phi 3P+CH2C(=O)-LDIFSDF + H](2+), fragments much more efficiently than the corresponding peptide with a fixed charge, an Arg and one added proton, [phi 3P+CH2C(=O)-LDIFSDFR + H](2+); both of these fragment more efficiently than the peptide with a fixed charge and no added proton, phi 3P+CH2C(=O)-LDIFSDF, MS/MS/MS (i.e., MS3) experimental results for b(n) ions formed at Asp-Xxx from phi 3P+CH2C(=O)-LDIFSDF and its H/D exchange derivative, phi 3P+CH2C(=O)-LDIFSDF-d(11), are consistent with the b(n) ions formed at Asp-Xxx having a succinic anhydride cyclic structure, MS/MS experiments were also carried out for phi 3P+CH2C(=O)-AAAA, a peptide derivative containing active hydrogens only at amide nitrogens plus the C-terminus, and its active H/D exchange product, phi 3P+CH2C(=O)-AAAA-d(5), The results show that a hydrogen originally located at an amide nitrogen is transferred away in the formation of a cyclic charge remote b ion.