Sudha Rajagopalan, Kohtani Motoya, Jarrold Martin F
Chemistry Department, Indiana University, Bloomington, Indiana 47405-7102, USA.
J Phys Chem B. 2005 Apr 7;109(13):6442-7. doi: 10.1021/jp045490m.
We have used ion-mobility mass spectrometry to examine the conformations of the protonated complex formed between AcA(7)KA(6)KK and AcEA(7)EA(7), helical alanine-based peptides that incorporate glutamic acid (E) and lysine (K). Designed interactions between the acidic E and basic K residues help to stabilize the complex, which is generated by electrospray and studied in the gas phase. There are two main conformations: (1) a coaxial linear arrangement where the helices are tethered together by an EKK interaction between the pair of lysines at the C-terminus of the AcA(7)KA(6)KK peptide and a glutamic acid at the N-terminus of the AcEA(7)EA(7) peptide and (2) a coiled-coil arrangement with side-by-side antiparallel helices where there is an additional EK interaction between the E and K residues in the middle of the helices. The coiled-coil opens up to the coaxial linear structure as the temperature is raised. Entropy and enthalpy changes for the opening of the coiled-coil were derived from the measurements. The enthalpy change indicates that the interaction between the E and K residues in the middle of the helices is a weak neutral hydrogen bond. The EKK interaction is significantly stronger.
我们使用离子淌度质谱法研究了AcA(7)KA(6)KK与AcEA(7)EA(7)（两种含有谷氨酸（E）和赖氨酸（K）的基于丙氨酸的螺旋肽）之间形成的质子化复合物的构象。酸性E残基和碱性K残基之间设计的相互作用有助于稳定该复合物，该复合物通过电喷雾产生并在气相中进行研究。存在两种主要构象：（1）一种同轴线性排列，其中螺旋通过AcA(7)KA(6)KK肽C端的一对赖氨酸与AcEA(7)EA(7)肽N端的一个谷氨酸之间的EKK相互作用连接在一起；（2）一种具有并排反平行螺旋的卷曲螺旋排列，其中螺旋中间的E和K残基之间存在额外的EK相互作用。随着温度升高，卷曲螺旋会转变为同轴线性结构。从测量中得出了卷曲螺旋打开过程中的熵变和焓变。焓变表明螺旋中间的E和K残基之间的相互作用是一种弱的中性氢键。EKK相互作用明显更强。
