The crystallization of amidase, the ultimate enzyme in the Trp-dependent auxin-biosynthesis pathway, from Arabidopsis thaliana was attempted using protein samples with at least 95% purity. Cube-shaped crystals that were assumed to be amidase crystals that belonged to space group I4 (unit-cell parameters a = b = 128.6, c = 249.7 Å) were obtained and diffracted to 3.0 Å resolution. Molecular replacement using structures from the PDB containing the amidase signature fold as search models was unsuccessful in yielding a convincing solution. Using the Sequence-Independent Molecular replacement Based on Available Databases (SIMBAD) program, it was discovered that the structure corresponded to dihydrolipoamide succinyltransferase from Escherichia coli (PDB entry 1c4t), which is considered to be a common crystallization contaminant protein. The structure was refined to an Rwork of 23.0% and an Rfree of 27.2% at 3.0 Å resolution. The structure was compared with others of the same protein deposited in the PDB. This is the first report of the structure of dihydrolipoamide succinyltransferase isolated without an expression tag and in this novel crystal form.

中文翻译：

---

新型晶体形式的大肠杆菌二氢硫辛酰胺琥珀酰转移酶催化结构域的结构：常见蛋白质结晶污染物的故事。


尝试使用纯度至少为 95% 的蛋白质样品从拟南芥中结晶酰胺酶（Trp 依赖性生长素生物合成途径中的最终酶）。获得了被认为是属于空间群 I4 的酰胺酶晶体的立方体晶体（晶胞参数 a = b = 128.6，c = 249.7 Å），并衍射至 3.0 Å 分辨率。使用包含酰胺酶特征折叠的 PDB 结构作为搜索模型的分子替换未能成功产生令人信服的解决方案。使用基于可用数据库的序列独立分子替换（SIMBAD）程序，发现该结构对应于大肠杆菌的二氢硫辛酰胺琥珀酰转移酶（PDB条目1c4t），其被认为是常见的结晶污染蛋白。该结构在 3.0 Å 分辨率下精炼至 Rwork 为 23.0%，Rfree 为 27.2%。该结构与 PDB 中沉积的相同蛋白质的其他结构进行了比较。这是首次报道二氢硫辛酸酰胺琥珀酰转移酶的结构，该酶没有表达标签且以这种新颖的晶型分离。