Brameld K A, Shrader W D, Imperiali B, Goddard W A
Materials and Process Simulation Center, Beckman Institute, Pasadena CA 91125, USA.
J Mol Biol. 1998 Jul 31;280(5):913-23. doi: 10.1006/jmbi.1998.1890.
Based on first principles and molecular mechanics calculations, we conclude that the mechanism of hevamine (a family 18 chitinase) involves an oxazoline ion intermediate stabilized by the neighboring C2' acetamido group. In this intermediate, the acetamido carbonyl oxygen atom forms a covalent bond to C1' of N-acetyl-glucosamine and has a transferred positive charge from the pyranose ring onto the acetamido nitrogen atom, leading to an anchimeric stabilization of 38.1 kcal/mol when docked with hevamine. This double displacement mechanism involving an oxazoline intermediate distinguishes the family 18 chitinase (which have one acidic residue near the active site) from family 19 chitinase and from hen egg-white lysozyme, which have two acidic residues near the active site. The structural and electronic properties of the oxazoline intermediate are similar to the known chitinase inhibitor allosamidin, suggesting that allosamidins act as transition state analogs of an oxazoline intermediate. Structural and electronic features of the oxazoline ion likely to be important in the design of new chitinase inhibitors are discussed.
基于第一性原理和分子力学计算，我们得出结论：hevamine（一种18族几丁质酶）的作用机制涉及一种由相邻的C2'乙酰氨基基团稳定的恶唑啉离子中间体。在该中间体中，乙酰氨基羰基氧原子与N-乙酰葡糖胺的C1'形成共价键，并从吡喃糖环转移一个正电荷到乙酰氨基氮原子上，当与hevamine对接时，导致38.1千卡/摩尔的邻基参与稳定作用。这种涉及恶唑啉中间体的双取代机制将18族几丁质酶（其活性位点附近有一个酸性残基）与19族几丁质酶以及鸡蛋清溶菌酶区分开来，后两者在活性位点附近有两个酸性残基。恶唑啉中间体的结构和电子性质与已知的几丁质酶抑制剂别洛沙米定相似，这表明别洛沙米定作为恶唑啉中间体的过渡态类似物起作用。文中还讨论了恶唑啉离子在设计新型几丁质酶抑制剂中可能重要的结构和电子特征。
