Granulocyte macrophage colony stimulating factor (GMCSF) is an immunomodulatory cytokine that is harnessed as a therapeutic. GMCSF is known to interact with other clinically important molecules, such as heparin, suggesting that endogenous and administered GMCSF has the potential to modulate orthogonal treatment outcomes. Thus, molecular level characterization of GMCSF and its interactions with biologically active compounds is critical to understanding these mechanisms and predicting clinical consequences. Here, we dissect the biophysical factors that facilitate the GMCSF–heparin interaction, previously shown to be pH-dependent, using nuclear magnetic resonance spectroscopy, surface plasmon resonance, and molecular dynamics simulations. We find that the affinity of GMCSF for heparin increases not only with a transition to acidic pH but also with an increase in heparin chain length. Changes in local flexibility, including a disruption of the N-terminal helix at acidic pH, also accompany the binding of heparin to GMCSF. We use molecular dynamics simulations to propose a mechanism in which a positive binding pocket that is not fully solvent accessible at neutral pH becomes more accessible at acidic pH, facilitating the binding of heparin to the protein.

中文翻译：

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映射pH敏感肝素结合粒细胞巨噬细胞集落刺激因子的结构和动态决定因素。

粒细胞巨噬细胞集落刺激因子（GMCSF）是一种免疫调节细胞因子，可用于治疗。已知GMCSF与其他临床上重要的分子（例如肝素）发生相互作用，这表明内源和给药的GMCSF具有调节正交治疗结果的潜力。因此，GMCSF的分子水平表征及其与生物活性化合物的相互作用对于理解这些机制和预测临床后果至关重要。在这里，我们使用核磁共振波谱，表面等离子体激元共振和分子动力学模拟来剖析了促进GMCSF-肝素相互作用的生物物理因素，以前证明这些作用是pH依赖性的。我们发现，GMCSF对肝素的亲和力不仅随着向酸性pH的过渡而增加，而且随着肝素链长的增加而增加。局部柔韧性的变化，包括在酸性pH下N末端螺旋的破坏，也伴随着肝素与GMCSF的结合。我们使用分子动力学模拟来提出一种机制，其中在中性pH下不能完全被溶剂完全吸收的正结合袋在酸性pH下变得更容易被利用，从而促进肝素与蛋白质的结合。