Jacobs C, Joris B, Jamin M, Klarsov K, Van Beeumen J, Mengin-Lecreulx D, van Heijenoort J, Park J T, Normark S, Frère J M
Centre d'Ingénierie des Protéines, Université de Liège, Belgium.
Mol Microbiol. 1995 Feb;15(3):553-9. doi: 10.1111/j.1365-2958.1995.tb02268.x.
In enterobacteria, the ampD gene encodes a cytosolic protein which acts as a negative regulator of beta-lactamase expression. It is shown here that the AmpD protein is a novel N-acetylmuramyl-L-alanine amidase (E.C.3.5.1.28) participating in the intracellular recycling of peptidoglycan fragments. Surprisingly, AmpD exhibits an exclusive specificity for substrates containing anhydro muramic acid. This anhydro bond is mainly found in the peptidoglycan degradation products formed by the periplasmic lytic transglycosylases and thus might behave as a 'recycling tag' allowing the enzyme to distinguish these fragments from the newly synthesized peptidoglycan precursors. The AmpD substrate (or substrates) which accumulates in the absence of the corresponding enzymatic activity acts as an intracellular positive effector for beta-lactamase expression and might represent an element of a communication network between the chromosome and the cell wall peptidoglycan.
在肠杆菌中，ampD基因编码一种胞质蛋白，该蛋白作为β-内酰胺酶表达的负调节因子。本文表明，AmpD蛋白是一种新型的N-乙酰胞壁酰-L-丙氨酸酰胺酶（E.C.3.5.1.28），参与肽聚糖片段的细胞内循环利用。令人惊讶的是，AmpD对含有脱水 muramic 酸的底物具有独特的特异性。这种脱水键主要存在于周质溶菌转糖基酶形成的肽聚糖降解产物中，因此可能作为一种“循环标签”，使该酶能够将这些片段与新合成的肽聚糖前体区分开来。在缺乏相应酶活性时积累的AmpD底物作为β-内酰胺酶表达的细胞内正效应物，可能代表染色体与细胞壁肽聚糖之间通讯网络的一个元件。
