Thioester analogues of peptidoglycan fragment MurNAc-L-Ala-γ-D-Glu as substrates for peptidoglycan hydrolase MurNAc-L-Ala amidase
作者:Ross L. Harding、Joanne Henshaw、Joannah Tilling、Timothy D. H. Bugg
DOI:10.1039/b200921h
日期:2002.7.11
MurNAc-L-amidase is one of a family of peptidoglycan hydrolases which catalyses the breakdown of bacterial peptidoglycan. Analogues of the peptidoglycan fragment MurNAc-L-Ala-γ-D-Glu containing S-thiolactic acid in place of L-alanine were synthesised as thioester substrates for this enzyme. Triphenylmethanethiol was used to develop a stereoselective synthesis of S-thiolactic acid, which was elaborated synthetically into MurNAc-dipeptide analogues. MurNAc-S-thioacetyl-N-propylamide 13 and MurNAc-S-thiolactyl-2R-alaninamide 16 were found not to be substrates for recombinant MurNAc-L-Ala amidases CwlA from Bacillus subtilis and Ply21 from bacteriophage TP21, however, turnover of tripeptide thioester S-propionylthiolactyl-γ-D-Glu-L-Lys-OMe 21 was observed using amidase Ply21. Therefore, recognition of the amino acid at position 3 of the pentapeptide sidechain appears to be important for enzymatic turnover.
MurNAc-L-酰胺酶是催化细菌肽聚糖分解的肽聚糖水解酶家族之一。合成了一种硫酯底物,即将肽聚糖片段MurNAc-L-Ala-γ-D-Glu中的L-丙氨酸替换为S-硫乳酸的类似物。利用三苯基甲硫醇开发了S-硫乳酸的手性选择性合成方法,并进一步合成了MurNAc二肽类似物。发现MurNAc-S-硫乙酰基-N-丙基酰胺13和MurNAc-S-硫乳酰基-2R-丙氨酰胺16不是枯草芽孢杆菌重组MurNAc-L-Ala酰胺酶CwlA和噬菌体TP21的Ply21的底物,但观察到三肽硫酯S-丙酰基硫乳酰基-γ-D-Glu-L-赖氨酸甲酯21在Ply21酰胺酶的作用下发生了转氨反应。因此,对于酶促转氨反应来说,识别五肽侧链上第3位的氨基酸似乎很重要。