缓激肽多肽片段间非共价作用的质谱研究

Investigation of the Non-Covalent Interactions between Fragment Peptides of Bradykinin by Mass Spectrometry

以缓激肽(R1P2P3G4F5S6P7F8R9)分子作为研究模型,用电喷雾质谱研究缓激肽分子碎片片段之间的非共价相互作用,探讨了影响气相多肽分子构象稳定的氢键作用.合成了与缓激肽分子在位置1断裂形成的碎片一致的RPPGFS和PFR多肽序列,与在位置2断裂形成碎片一致的RPPGF和SPFR多肽,以及N端或者C端去掉精氨酸的相应碎片多肽.实验结果表明,上述两个断裂位置产生的碎片多肽分别进行反应后,都能发生非共价作用.在断裂方式1下,PFR多肽在去掉C端的精氨酸R后,与其他大多数多肽不发生非共价结合,表明PFR中的R在缓激肽气相分子的构象中发挥重要的作用.而在断裂方式2下,去掉N端或者C端精氨酸的多肽之间都存在非共价结合,即C端带有丝氨酸的SPF或SPFR多肽碎片仍然可以与N端碎片发生氢键结合,表明丝氨酸很可能处于转角的位置.通过对碰撞诱导解离(CID)的碰撞能量分析,发现多肽RPPGFS和PFR,以及多肽RPPGF和SPFR之间氢键结合较强,而同时去掉N端和C端精氨酸得到的多肽之间的氢键结合较弱.质谱滴定法定量测得的RPPGFS和PFR的结合常数为3.53×103,与RPPGF和SPFR的结合常数(3.16×103)相接近,它们均大于去除精氨酸的PPGF和SPF的结合常数(1.25×103).质谱滴定实验结果进一步确认了碰撞诱导解离的分析结果,表明缓激肽分子两端的精氨酸之间的氢键作用是气相缓激肽分子构象稳定的重要因素之一.

To explore the important factors affecting the stability of gas phase bradykinin （R1P2P3G4F5S6P7F8R9）, the non-covalent interactions between fragment peptides of bradykinin were investigated by electrospray ionization mass spectrometry （ESI-MS）. The fracture sites are S6P7 （mode 1） and F5S6 （mode 2）. The fragment peptides of bradykinin and its des-arginine analogues were synthesized. ESI-MS results showed that the fragment peptides of bradykinin obtained in the two modes can easily react by non-covalent interactions. In fracture mode 1, when R9 was removed, the peptide PF seldom bound to any other fragment peptide. While in fracture mode 2, non-covalent binding still occurred between fragment peptides when either R1 or R9 was removed, which indicates that serine is likely to be at the position of the β-turn. The collision induced dissociation （CID） revealed that the binding strength between RPPGFS and PFR, or RPPGF and SPFR, is stronger than for the peptides without R. For the complexes of RPPGFS with PFR, and RPPGF with SPFR, the binding constant （Kst） values determined by mass spectrometric titrations were 3.53x 103 and 3.16x 103, respectively, which are greater than the Kst value （1.25x 103） of the complexesof PPGF with SPF. The mass spectrometric titrations confirmed the results from CID, indicating that the hydrogen bonds between the arginine residues of the two terminals of bradykinin play an important role in stabilizing the conformation of gas phase bradykinin.