Instituto de Biología Molecular y Celular, Universidad Miguel Hernández, Elche, Alicante, Spain.
PLoS One. 2011 Feb 22;6(2):e17068. doi: 10.1371/journal.pone.0017068.
Thioredoxins (TRXs) are ubiquitous proteins involved in redox processes. About forty genes encode TRX or TRX-related proteins in plants, grouped in different families according to their subcellular localization. For instance, the h-type TRXs are located in cytoplasm or mitochondria, whereas f-type TRXs have a plastidial origin, although both types of proteins have an eukaryotic origin as opposed to other TRXs. Herein, we study the conformational and the biophysical features of TRXh1, TRXh2 and TRXf from Pisum sativum. The modelled structures of the three proteins show the well-known TRX fold. While sharing similar pH-denaturations features, the chemical and thermal stabilities are different, being PsTRXh1 (Pisum sativum thioredoxin h1) the most stable isoform; moreover, the three proteins follow a three-state denaturation model, during the chemical-denaturations. These differences in the thermal- and chemical-denaturations result from changes, in a broad sense, of the several ASAs (accessible surface areas) of the proteins. Thus, although a strong relationship can be found between the primary amino acid sequence and the structure among TRXs, that between the residue sequence and the conformational stability and biophysical properties is not. We discuss how these differences in the biophysical properties of TRXs determine their unique functions in pea, and we show how residues involved in the biophysical features described (pH-titrations, dimerizations and chemical-denaturations) belong to regions involved in interaction with other proteins. Our results suggest that the sequence demands of protein-protein function are relatively rigid, with different protein-binding pockets (some in common) for each of the three proteins, but the demands of structure and conformational stability per se (as long as there is a maintained core), are less so.
硫氧还蛋白（TRXs）是参与氧化还原过程的普遍存在的蛋白质。大约四十个基因在植物中编码 TRX 或 TRX 相关蛋白，根据它们的亚细胞定位分为不同的家族。例如，h 型 TRX 位于细胞质或线粒体中，而 f 型 TRX 具有质体起源，尽管这两种类型的蛋白质都具有真核起源，而不是其他 TRX。本文研究了豌豆（Pisum sativum）TRXh1、TRXh2 和 TRXf 的构象和生物物理特性。这三种蛋白质的模型结构显示了众所周知的 TRX 折叠。虽然它们具有相似的 pH 变性特征，但化学和热稳定性不同，PsTRXh1（豌豆硫氧还蛋白 h1）是最稳定的同工型；此外，三种蛋白质在化学变性过程中遵循三态变性模型。这些在热变性和化学变性中的差异源于蛋白质几个 ASA（可及表面积）的广泛变化。因此，尽管在 TRX 之间可以发现一级氨基酸序列和结构之间存在很强的关系，但在残基序列和构象稳定性和生物物理性质之间不存在这种关系。我们讨论了 TRX 生物物理性质的这些差异如何决定它们在豌豆中的独特功能，并展示了描述的生物物理特征（pH 滴定、二聚化和化学变性）涉及的残基如何属于涉及与其他蛋白质相互作用的区域。我们的结果表明，蛋白质-蛋白质功能的序列需求相对严格，三种蛋白质中的每一种都有其独特的蛋白结合口袋（有些是共同的），但结构和构象稳定性本身的需求（只要保持核心）则不那么严格。
