Fixed charge chemical modifications on peptides and proteins can impact fragmentation behaviors in tandem mass spectrometry (MS/MS). In this study, we employed a thiol-specific cationic alkylation reagent, (4-iodobutyl)triphenylphosphonium (IBTP), to selectively modify cysteine thiol groups in mitochondrial proteome samples. Tandem mass spectrometric characteristics of butyltriphenylphosphonium (BTP)-modified peptides were evaluated by comparison to their carbamidomethylated (CAM) analogues using a quadrupole time-of-flight (Q-TOF) instrument under low energy collision-induced dissociation (CID) conditions. Introduction of the fixed charge modification resulted in the observation of peptide and fragment (bn and yn) ions with higher charge states than those observed for CAM-modified analogues. The charged BTP moiety had a significant effect on the neighboring amide bond fragmentation products. A decrease in relative abundances of the product ions at the corresponding cleavage sites was observed compared with those from the CAM-modified derivatives. This effect was particularly noticeable when an Xxx-Pro bond was in the vicinity of a BTP group. We hypothesized that the presence of a phosphonium moiety will reduce the tendency for protonation of the proximal amide bonds in the peptide backbone. Indeed, calculations indicated that proton affinities of backbone amide bonds close to the modified cysteine residues were generally 20–50 kcal/mol lower for BTP-modified peptides than for the unmodified or CAM-modified analogues with the sequence motif -Ala-Cys-Alan-Ala2-, -Ala-Cys-Alan-Pro-Ala-, and -Ala-Pro-Alan-Cys-Ala-, n = 0–3.
肽和蛋白质上的固定电荷
化学修饰会影响串联质谱(MS/MS)的碎片行为。在这项研究中,我们采用了一种
硫醇特异性阳离子烷基化试剂--(4-
碘丁基)
三苯基膦(IBTP)来选择性地修饰线粒体蛋白质组样品中的半胱
氨酸
硫醇基团。在低能量碰撞诱导解离(CID)条件下,使用四极杆飞行时间(Q-TOF)仪器,将丁基
三苯基膦(BTP)修饰的肽与其
氨基甲基化(CAM)类似物进行比较,评估了它们的串联质谱特性。引入固定电荷修饰后,肽和片段(bn 和 yn)离子的电荷状态高于 CAM 修饰类似物的电荷状态。带电的 BTP 分子对邻近的酰胺键碎片产物有显著影响。与 CAM 改性衍
生物相比,在相应的裂解位点上观察到的产物离子相对丰度有所下降。当 Xxx-Pro 键位于 BTP 基团附近时,这种影响尤为明显。我们推测,
鏻分子的存在会降低肽骨近端酰胺键的质子化倾向。计算结果表明,与未修饰或 CAM 修饰的类似物相比,BTP 修饰的肽在靠近修饰的半胱
氨酸残基的骨架酰胺键上的质子亲和力一般要低 20-50 kcal/mol,序列基序为 -Ala-Cys-Alan-Ala2-、-Ala-Cys-Alan-Pro-Ala- 和 -Ala-Pro-Alan-Cys-Ala-,n = 0-3。