Nemirovskiy O V, Gross M L
Chemistry Department, Washington University, St. Louis, MO 63130, USA.
J Am Soc Mass Spectrom. 1998 Oct;9(10):1020-8. doi: 10.1016/S1044-0305(98)00071-3.
Low-energy (LE) and high-energy (HE) collisionally activated decompositions (CAD) of calcium/peptide complexes of the form [M - H + Ca]+ and [M + Ca]2+ reflect the site of calcium binding in various gas-phase peptides that are models of the calcium binding site III of rabbit skeletal troponin C. The Ca2+ binding sites involve an aspartic acid, glutamic acid, and asparagine, which are in the metal-binding loops of calcium-binding proteins. Both fast atom bombardment (FAB) and electrospray ionization (ESI) were used to generate the metal/peptide complexes. When submitted to LE CAD, ESI-produced Ca2+/peptide complexes undergo fragmentations that are controlled by Ca2+ binding and provide information on the Ca2+ binding site. The LE CAD spectra are simple, indicating that Ca2+ binding involves specific oxygen ligands including acidic side chains and that only a few low-energy fragmentation channels exist. The HE CAD spectra of FAB-produced Ca2+/peptide complexes are more complex, owing to the introduction of high internal energy into the precursor ion. Interactions of the other alkaline-earth metal ions Mg2+ and Ba2+ with these peptides reveal that the ligand preferences of these metal ions are slightly different than those of Ca2+.
[M - H + Ca]+和[M + Ca]2+形式的钙/肽复合物的低能（LE）和高能（HE）碰撞活化分解（CAD）反映了各种气相肽中钙结合的位点，这些肽是兔骨骼肌肌钙蛋白C钙结合位点III的模型。Ca2+结合位点涉及天冬氨酸、谷氨酸和天冬酰胺，它们存在于钙结合蛋白的金属结合环中。快速原子轰击（FAB）和电喷雾电离（ESI）都用于生成金属/肽复合物。当进行LE CAD时，ESI产生的Ca2+/肽复合物会发生受Ca2+结合控制的碎片化，并提供有关Ca2+结合位点的信息。LE CAD光谱很简单，表明Ca2+结合涉及特定的氧配体，包括酸性侧链，并且只存在少数低能碎片化通道。由于将高内能引入前体离子，FAB产生的Ca2+/肽复合物的HE CAD光谱更复杂。其他碱土金属离子Mg2+和Ba2+与这些肽的相互作用表明，这些金属离子的配体偏好与Ca2+的略有不同。
