Center for Biotechnology, Federal University of Rio Grande do Sul (UFRGS), CP 15005, Porto Alegre, RS 91501-970, Brazil.
Glycobiology. 2017 Dec 1;27(12):1109-1119. doi: 10.1093/glycob/cwx080.
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.
植物生长素对于植物生长和发育至关重要。主要的天然植物生长素是吲哚-3-乙酸（IAA），而 1-萘乙酸（NAA）是一种合成形式。生长素结合蛋白 1（ABP1）特异性结合生长素，可能在非转录细胞反应中充当受体。先前已在玉米中以 1.9 Å 的分辨率确定了 ABP1 的结构。为了进一步深入了解 ABP1 的结构生物学，本研究对玉米和拟南芥的寡聚糖基化蛋白的完整模型进行了分子动力学模拟，这些模型存在或不存在生长素。在玉米中，Zn2+配位和糖基化都促进了构象稳定性，而大部分稳定效应都位于 N 端区域。两种物种的 ABP1 的 C 端区域的α螺旋在模拟过程中展开，在玉米中呈现出更伸展的结构。在拟南芥中，螺旋似乎更稳定，在大多数单体模拟中都得以保留，而在蛋白质呈二聚体形式时则展开。在拟南芥 ABP1 与 IAA 或 NAA 结合时，糖基化结构围绕着蛋白质排列，覆盖了生长素进入或离开的假定部位。与结合 IAA 的情况相比，NAA 结合的蛋白质折叠更类似于晶体结构，显示出更高的稳定性。在两种物种和生长素类型之间发现的 ABP1 的分子结构差异表明，这种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表现出功能特异性。
