Demir Ozlem, Roitberg Adrian E
Department of Chemistry and Quantum Theory Project, University of Florida, Gainesville, Florida 32611-8435, USA.
Biochemistry. 2009 Apr 21;48(15):3398-406. doi: 10.1021/bi802230y.
trans-Sialidase is an essential enzyme for Trypanosoma cruzi, the causative agent of Chagas' disease, to escape from the host immune system and to invade the host cells. Therefore, T. cruzi trans-sialidase (TcTS) presents a potential and appealing therapeutic target for this lethal disease. The availability of a structurally very similar enzyme with strict hydrolase activity (Trypanosoma rangeli sialidase, TrSA) provides us a unique opportunity to understand the determinants of their structure and catalytic mechanism. In this study, we compare the catalytic cleft plasticity of free (apo) and ligand-bound (holo) forms of the two enzymes using molecular dynamics simulations. We focus on the mouth of the catalytic cleft that is defined by two residues: W312 and Y119 in TcTS and W312 and S119 in TrSA. Our results indicate that TcTS has a very flexible, widely open catalytic cleft, mostly due to W312 loop motion, in apo form. However, when the catalytic cleft is occupied by a ligand, the flexibility and solvent exposure of TcTS is significantly reduced. On the other hand, TrSA maintains a more open catalytic cleft compared to its crystal structures in both apo and holo forms (and compared to TcTS in holo forms). The reduced solvent exposure of TcTS catalytic cleft might be partially or fully responsible for TcTS to be a less efficient hydrolase than TrSA.
转唾液酸酶是克氏锥虫（恰加斯病的病原体）逃避宿主免疫系统并侵入宿主细胞所必需的酶。因此，克氏锥虫转唾液酸酶（TcTS）是这种致命疾病潜在且有吸引力的治疗靶点。一种具有严格水解酶活性且结构非常相似的酶（兰氏锥虫唾液酸酶，TrSA）的存在，为我们提供了一个独特的机会来了解它们的结构和催化机制的决定因素。在本研究中，我们使用分子动力学模拟比较了这两种酶的游离（无配体）和配体结合（有配体）形式的催化裂隙可塑性。我们关注由两个残基定义的催化裂隙口：TcTS中的W312和Y119以及TrSA中的W312和S119。我们的结果表明，在无配体形式下，TcTS具有非常灵活、广泛开放的催化裂隙，这主要归因于W312环的运动。然而，当催化裂隙被配体占据时，TcTS的灵活性和溶剂暴露显著降低。另一方面，与无配体和有配体形式的晶体结构相比（以及与有配体形式的TcTS相比），TrSA保持更开放的催化裂隙。TcTS催化裂隙的溶剂暴露减少可能部分或完全导致TcTS作为水解酶的效率低于TrSA。
