Lindquist S, Galleni M, Lindberg F, Normark S
Department of Microbiology, University of Umeå, Sweden.
Mol Microbiol. 1989 Aug;3(8):1091-102. doi: 10.1111/j.1365-2958.1989.tb00259.x.
The cloned Citrobacter freundii ampC beta-lactamase is inducible in the presence of its regulatory gene ampR in Escherichia coli (Lindberg et al., 1985). The basal level of expression and inducibility are affected by two E. coli proteins encoded by the closely linked ampD and ampE genes. Deletion of both genes led to constitutive ampR-dependent overproduction of beta-lactamase, whereas an out-of-frame deletion in AmpD caused the basal expression to increase two-fold. This ampD1 mutant was inducible at lower beta-lactam concentrations than the wild type. An IS1 insertion in ampD was polar on ampE expression and increased basal beta-lactamase expression 30-fold while mediating a semi-constitutive phenotype. AmpE expressed from a recombinant plasmid in an ampD-ampE deletion mutant reduced basal beta-lactamase expression to wild-type levels but did not markedly reduce beta-lactam resistance since the cells became hyperinducible. In the absence of AmpD, increasing levels of AmpE therefore decrease the basal expression of AmpC beta-lactamase in an AmpR-dependent manner. AmpD modulated the response exerted on beta-lactamase expression by AmpE. The ampD gene encodes a 20.5kD cytoplasmic protein while the 32.1kD ampE gene product is an integral membrane protein with a likely ATP-binding site between the second and third putative transmembrane region. Since neither AmpD nor AmpE are needed for beta-lactam induction and since these proteins could not be covalently labelled by benzylpenicillin, they are not thought to act as beta-lactam-binding sensory transducers. Instead it is suggested that AmpD and AmpE sense the effect of beta-lactam action on peptidoglycan biosynthesis and relay this signal to AmpR.
克隆的弗氏柠檬酸杆菌AmpCβ-内酰胺酶在其调控基因ampR存在的情况下，在大肠杆菌中是可诱导的（Lindberg等人，1985年）。其基础表达水平和诱导性受紧密连锁的ampD和ampE基因编码的两种大肠杆菌蛋白影响。这两个基因的缺失导致β-内酰胺酶在ampR依赖的情况下组成型过量产生，而AmpD中一个移码缺失导致基础表达增加两倍。这个ampD1突变体在比野生型更低的β-内酰胺浓度下即可被诱导。ampD中的一个IS1插入对ampE表达具有极性影响，并使基础β-内酰胺酶表达增加30倍，同时介导一种半组成型表型。在ampD-ampE缺失突变体中，由重组质粒表达的AmpE将基础β-内酰胺酶表达降低到野生型水平，但由于细胞变得超诱导，并未显著降低β-内酰胺抗性。因此，在没有AmpD的情况下，AmpE水平的增加以ampR依赖的方式降低AmpCβ-内酰胺酶的基础表达。AmpD调节AmpE对β-内酰胺酶表达的作用。ampD基因编码一种20.5kD的细胞质蛋白，而32.1kD的ampE基因产物是一种整合膜蛋白，在第二个和第三个假定的跨膜区域之间可能有一个ATP结合位点。由于β-内酰胺诱导不需要AmpD和AmpE，且这些蛋白不能被苄青霉素共价标记，因此它们不被认为是作为β-内酰胺结合的传感转导器起作用。相反，有人认为AmpD和AmpE感知β-内酰胺作用对肽聚糖生物合成的影响，并将此信号传递给AmpR。
