Michalska Karolina, Borek Dominika, Hernández-Santoyo Alejadra, Jaskolski Mariusz
Department of Crystallography, Faculty of Chemistry, A. Mickiewicz University, Poznan, Poland.
Acta Crystallogr D Biol Crystallogr. 2008 Mar;64(Pt 3):309-20. doi: 10.1107/S0907444907068072. Epub 2008 Feb 20.
Plant-type L-asparaginases hydrolyze the side-chain amide bond of L-asparagine or its beta-peptides. They belong to the N-terminal nucleophile (Ntn) hydrolases and are synthesized as inactive precursor molecules. Activation occurs via the autoproteolytic release of two subunits, alpha and beta, the latter of which carries the nucleophile at its N-terminus. Crystallographic studies of plant-type asparaginases have focused on an Escherichia coli homologue (EcAIII), which has been crystallized in several crystal forms. Although they all belong to the same P2 1 2 1 2 1 space group with similar unit-cell parameters, they display different crystal-packing arrangements and thus should be classified as separate polymorphs. This variability stems mainly from different positions of the EcAIII molecules within the unit cell, although they also exhibit slight differences in orientation. The intermolecular interactions that trigger different crystal lattice formation are mediated by ions, which represent the most variable component of the crystallization conditions. This behaviour confirms recent observations that small molecules might promote protein crystal lattice formation.
植物型L-天冬酰胺酶可水解L-天冬酰胺或其β-肽的侧链酰胺键。它们属于N-末端亲核体（Ntn）水解酶，以无活性前体分子形式合成。激活通过两个亚基α和β的自蛋白水解释放发生，后者在其N-末端携带亲核体。植物型天冬酰胺酶的晶体学研究集中在大肠杆菌同系物（EcAIII）上，它已以几种晶体形式结晶。尽管它们都属于具有相似晶胞参数的同一P2 1 2 1 2 1空间群，但它们显示出不同的晶体堆积排列，因此应归类为不同的多晶型物。这种变异性主要源于EcAIII分子在晶胞内的不同位置，尽管它们在取向上也表现出细微差异。引发不同晶格形成的分子间相互作用由离子介导，离子是结晶条件中最可变的成分。这种行为证实了最近的观察结果，即小分子可能促进蛋白质晶格形成。
