Oh Kwang-Im, Fiorin Giacomo, Gai Feng
Department of Chemistry, University of Pennsylvania, 231 S. 34th Street, Philadelphia, PA, 19104-6323, USA.
Institute for Computational Molecular Science, Temple University, 1925 North 12th Street, Philadelphia, PA, 19122-1801, USA.
Chemphyschem. 2015 Dec 1;16(17):3595-8. doi: 10.1002/cphc.201500777. Epub 2015 Oct 12.
Site-selective isotopic labeling of amide carbonyls offers a nonperturbative means to introduce a localized infrared probe into proteins. Although this strategy has been widely used to investigate various biological questions, the dependence of the underlying amide I vibrational frequency on electric fields (or Stark tuning rate) has not been fully determined, which prevents it from being used in a quantitative manner in certain applications. Herein, through the use of experiments and molecular dynamics simulations, the Stark tuning rate of the amide I vibration of an isotopically labeled backbone carbonyl in a transmembrane α-helix is determined to be approximately 1.4 cm(-1) /(MV/cm). This result provides a quantitative basis for using this vibrational model to assess local electric fields in proteins, among other applications. For instance, by using this value, we are able to show that the backbone region of a dipeptide has a surprisingly low dielectric constant.
酰胺羰基的位点选择性同位素标记提供了一种将局部红外探针引入蛋白质的非扰动方法。尽管该策略已被广泛用于研究各种生物学问题，但酰胺I振动频率对电场的依赖性（或斯塔克调谐率）尚未完全确定，这使得它在某些应用中无法以定量方式使用。在此，通过实验和分子动力学模拟，确定了跨膜α-螺旋中同位素标记的主链羰基的酰胺I振动的斯塔克调谐率约为1.4 cm(-1) /(MV/cm)。该结果为使用该振动模型评估蛋白质中的局部电场等应用提供了定量基础。例如，通过使用该值，我们能够表明二肽的主链区域具有惊人的低介电常数。
