Thunnissen A M, Rozeboom H J, Kalk K H, Dijkstra B W
Laboratory of Biophysical Chemistry, University of Groningen, The Netherlands.
Biochemistry. 1995 Oct 3;34(39):12729-37. doi: 10.1021/bi00039a032.
Bulgecins are O-sulfonated glycopeptides that are able to enhance the antibacterial activity of beta-lactam antibiotics. The 70-kDa soluble lytic transglycosylase (SLT70) from Escherichia coli forms a specific target of these compounds. Using X-ray crystallography, the three-dimensional structure of a complex of SLT70 with bulgecin A has been determined to 2.8-A resolution and refined to an R factor of 19.5%. The model contains all 618 amino acids of SLT70 and a single molecule of bound bulgecin, located in the active site of the enzyme. The glycopeptide inhibitor is bound in an extended conformation occupying sites analogous to the B, C, and D subsites of lysozyme. Upon binding of bulgecin, the three-stranded antiparallel beta-sheet in the C domain shows a pronounced shift toward the inhibitor. In subsite D, the proposed catalytic residue Glu478 forms a hydrogen bond to the hydroxymethyl oxygen of the proline part of bulgecin and interacts electrostatically with the proline NH2+ group. These interactions, in addition to the interactions observed for the 2-acetamido group of the N-acetylglucosamine residue bound in subsite C, may explain the strong inhibition of SLT70 activity by bulgecin, suggesting that bulgecin acts as an analogue of an oxocarbonium ion intermediate in the reaction catalyzed by SLT70. The structure of the SLT70--bulgecin A complex may be of assistance in the rational design of novel antibiotics.
凸起菌素是O-磺化糖肽，能够增强β-内酰胺抗生素的抗菌活性。来自大肠杆菌的70 kDa可溶性溶菌转糖基酶（SLT70）是这些化合物的一个特定靶点。利用X射线晶体学，已确定SLT70与凸起菌素A复合物的三维结构，分辨率达到2.8 Å，并精修至R因子为19.5%。该模型包含SLT70的所有618个氨基酸以及一个位于酶活性位点的结合态凸起菌素单分子。糖肽抑制剂以伸展构象结合，占据类似于溶菌酶B、C和D亚位点的位置。在凸起菌素结合后，C结构域中的三股反平行β-折叠向抑制剂方向发生明显移动。在亚位点D中，推测的催化残基Glu478与凸起菌素脯氨酸部分的羟甲基氧形成氢键，并与脯氨酸NH2+基团发生静电相互作用。除了在亚位点C中观察到的与结合的N-乙酰葡糖胺残基的2-乙酰氨基基团的相互作用外，这些相互作用可能解释了凸起菌素对SLT70活性的强烈抑制，表明凸起菌素在SLT70催化的反应中充当氧鎓离子中间体的类似物。SLT70-凸起菌素A复合物的结构可能有助于新型抗生素的合理设计。
