精氨酸残基在质子化多肽RRMKWKK的气相碰撞诱导解离过程中的作用

用ESI/MS-MS方法研究了质子化多肽RRMKWKK 在低能气相碰撞诱导解离(CID)条件下的碰撞能和解离路径. 研究结果表明, M+2H]2+和M+3H]3+的CID断裂曲线和断裂位点相似. 但质子化多肽所含正电荷个数不同时, 产生同一碎片离子的初始碰撞能不同. 碱性氨基酸残基精氨酸(Arg)的支链是多肽RRMKWKK质子化时质子优先结合的位点, 导致含有Arg的多肽在气相碰撞诱导解离条件下解离时需要较高的碰撞能. 在用质谱方法研究含精氨酸残基的多肽时应选择质子个数比多肽中Arg个数多1个的母体离子. 质子化多肽RRMKWKK的结构AM1计算结果表明, 质子化RRMKWKK中两个相邻精氨酸在空间上相互分离, 库伦斥力的影响不足以改变质子的优先结合位点.

Effect of Arginine Residue on the Fragmentation of Protonated Peptide RRMKWKK Under Collision-induced Dissociation

Collision energy and fragmentation pathways of doubly-and triply-protonated peptide RRMKWKK upon low-energy collision-induced dissociation(CID) were investigated with ESI-MS/MS. Triply-protonated ion dissociated more easily than the doubly-protonated ion,with a dependence of the number of charges vs. the number of the arginine residues in the peptide. The two basic Arg residues were the primary charge location,resulted in a high dissociation energy for Arg-contained peptides. The protonated ions with one more proton than the number of Arg residues in the peptides were suggested when Arg-containing peptides were studied by using mass spectroscopy. Secondary structures of the protonated RRMKWKK calculated by AM1 method indicate that the two protons locating at the basic side chains of the two adjacent Arg were separated in space,so that Coulomb repulsion did not affect the proton location.