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首页> 外文期刊>Biochemistry >Thermodynamic analysis of the heparin interaction with a basic cyclic peptide using isothermal titration calorimetry
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Thermodynamic analysis of the heparin interaction with a basic cyclic peptide using isothermal titration calorimetry

机译：等温滴定热法分析肝素与碱性环肽相互作用的热力学

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摘要

Brain natriuretic peptide (BNP) was examined as part of a continuing study of the interaction of proteins and peptides with the glycosaminoglycan heparin. BNP was tentatively identified as a heparin-binding protein on the basis of its cyclic structure and the high frequency of the basic amino acid residues, lysine and arginine. Thermodynamic analysis using isothermal titration calorimetry confirmed heparin binding to BNP with a micromolar K-d. Surprisingly, despite the high frequency (22%) of basic residues in BNP, only a small portion of the free energy of this interaction resulted from ionic contributions under physiologic conditions. The contribution of polar amino acids, representing 28% of BNP, was next examined in a variety of different buffers. These experiments demonstrated the transfer of five protons from buffer to BNP on heparin binding, suggesting that hydrogen bonding between the polar residues of BNP and heparin is a major factor contributing to the free energy of BNP binding to heparin. Hydrophobic forces apparently play only a small role in binding. Heparin contains few nonpolar functional groups, and a positive change in heat capacity (Delta C-p = 1 kcal/mol) demonstrates the loss of polar residues on BNP-heparin binding. [References: 32]
机译：作为蛋白质和肽与糖胺聚糖肝素相互作用的持续研究的一部分，检查了脑利钠肽（BNP）。根据BNP的环状结构和碱性氨基酸残基（赖氨酸和精氨酸）的高频率，初步确定其为肝素结合蛋白。使用等温滴定量热法进行的热力学分析证实了肝素以微摩尔K-d结合BNP。令人惊讶的是，尽管BNP中碱性残基的频率很高（22％），但这种相互作用的自由能中只有一小部分是由生理条件下的离子贡献所致。下一步，在各种不同的缓冲液中检查了代表BNP 28％的极性氨基酸的贡献。这些实验证明了肝素结合后，五个质子从缓冲液转移到BNP，这表明BNP和肝素的极性残基之间的氢键是导致BNP结合肝素的自由能的主要因素。疏水力显然只在结合中起很小的作用。肝素包含很少的非极性官能团，并且热容量的正变化（Delta C-p = 1 kcal / mol）表明BNP-肝素结合时极性残基的损失。 [参考：32]

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