Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, Elche, Spain.
PLoS One. 2013;8(2):e56904. doi: 10.1371/journal.pone.0056904. Epub 2013 Feb 15.
Phasins are intracellular polyhydroxyalkanoat4e (PHA)-associated proteins involved in the stabilization of these bacterial carbon storage granules. Despite its importance in PHA metabolism and regulation, only few reports have focused so far on the structure of these proteins. In this work we have investigated the structure and stability of the PhaF phasin from Pseudomonas putida KT2440, a protein that is involved in PHA granule stabilization and distribution to daughter cells upon cell division. A structural, three-dimensional model of the protein was built from homology modeling procedures and consensus secondary structure predictions. The model predicts that PhaF is an elongated protein, with a long, amphipathic N-terminal helix with PHA binding capacity, followed by a short leucine zipper involved in protein oligomerization and a superhelical C-terminal domain wrapped around the chromosomal DNA. Hydrodynamic, spectroscopical and thermodynamic experiments validated the model and confirmed both that free PhaF is a tetramer in solution and that most part of the protein is intrinsically disordered in the absence of its ligands. The results lay a molecular basis for the explanation of the biological role of PhaF and, along with an exhaustive analysis of phasin sequence databases, suggest that intrinsic disorder and oligomerization through coiled-coils may be a widespread mechanism among these proteins.
phasins 是细胞内多羟基烷酸酯 4e (PHA) 相关蛋白，参与这些细菌碳储存颗粒的稳定。尽管它在 PHA 代谢和调节中很重要，但迄今为止，只有少数报道集中在这些蛋白质的结构上。在这项工作中，我们研究了来自假单胞菌 KT2440 的 PhaF 相蛋白的结构和稳定性，该蛋白参与 PHA 颗粒的稳定和在细胞分裂时向子细胞的分配。通过同源建模程序和共识二级结构预测，构建了该蛋白的结构三维模型。该模型预测 PhaF 是一种长形蛋白，具有带 PHA 结合能力的长、两亲性 N 端螺旋，其后是短亮氨酸拉链，参与蛋白寡聚化，以及围绕染色体 DNA 的超螺旋 C 端结构域。流体力学、光谱学和热力学实验验证了该模型，并证实游离 PhaF 在溶液中是一个四聚体，并且在没有其配体的情况下，大部分蛋白是无规卷曲的。这些结果为 PhaF 的生物学作用的解释奠定了分子基础，并且通过对相蛋白序列数据库的详尽分析，表明无规卷曲和通过卷曲螺旋的寡聚化可能是这些蛋白中的一种广泛机制。
