Auxin is critical for plant growth and development. The main natural auxin is indole-3-acetic acid (IAA), whereas 1-naphthalene acetic acid (NAA) is a synthetic form. Auxin-Binding Protein 1 (ABP1) specifically binds auxins, presumably playing roles as receptor in nontranscriptional cell responses. ABP1 structure was previously established from maize at 1.9 Å resolution. To gain further insight on ABP1 structural biology, this study was carried out employing molecular dynamics simulations of the complete models of the oligomeric glycosylated proteins from maize and Arabidopsis thaliana with or without auxins. In maize, both Zn²⁺ coordination and glycosylation promoted conformational stability and most of such stabilization effect was located on the N-terminal region. The α-helix of C-terminal regions in ABP1 of both species unfolded during simulations, assuming a more extended structure in maize. In Arabidopsis, the helix appeared more stable, being preserved in most of the monomeric simulations and unfolding when the protein was in the dimeric form. In Arabidopsis ABP1 bound to IAA or NAA, glycosylation structures arranged around the protein, covering the putative site of entrance or egress of auxin. NAA bound protein folding was more similar to the crystal structure showing higher stability compared to that of IAA bound. The molecular structural differences of ABP1 found between the species and auxin types indicate that this auxin-binding protein shows functional specificities in dicots and monocots, as well as in auxin type binding.

中文翻译：

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Zn2 +，二聚化和N-糖基化在生长素结合蛋白1（ABP1）与不同生长素相互作用中的作用

生长素对于植物生长和发育至关重要。主要的天然生长素是吲哚-3-乙酸（IAA），而1-萘乙酸（NAA）是合成形式。生长素结合蛋白1（ABP1）特异性结合生长素，大概在非转录细胞反应中起受体的作用。先前以1.9Å的分辨率从玉米建立了ABP1结构。为了获得对ABP1结构生物学的进一步了解，本研究利用分子动力学模拟玉米或拟南芥中含或不含生长素的寡聚糖基化蛋白的完整模型。玉米中Zn ²⁺配位和糖基化促进构象稳定性，并且大多数这种稳定作用位于N末端区域。假设玉米中的结构更扩展，则两个物种的ABP1的C端区域的α螺旋在模拟过程中均会展开。在拟南芥中，螺旋线似乎更稳定，在大多数单体模拟中都保留下来，并且当蛋白质为二聚体形式时会展开。在拟南芥中ABP1与IAA或NAA结合，糖基化结构围绕蛋白质排列，覆盖了生长素进入或流出的假定位点。与IAA结合的蛋白质折叠相比，NAA结合的蛋白质折叠与晶体结构更相似，显示出更高的稳定性。在种和生长素类型之间发现的ABP1的分子结构差异表明该生长素结合蛋白在双子叶植物和单子叶植物以及生长素类型结合中显示出功能特异性。