Roelofs J, Snippe H, Kleineidam R G, Van Haastert P J
Department of Biochemistry, University of Groningen, Nijenborgh 4, 9747AG Groningen, The Netherlands.
Biochem J. 2001 Mar 15;354(Pt 3):697-706. doi: 10.1042/0264-6021:3540697.
The core of adenylate and guanylate cyclases is formed by an intramolecular or intermolecular dimer of two cyclase domains arranged in an antiparallel fashion. Metazoan membrane-bound adenylate cyclases are composed of 12 transmembrane spanning regions, and two cyclase domains which function as a heterodimer and are activated by G-proteins. In contrast, membrane-bound guanylate cyclases have only one transmembrane spanning region and one cyclase domain, and are activated by extracellular ligands to form a homodimer. In the cellular slime mould, Dictyostelium discoideum, membrane-bound guanylate cyclase activity is induced after cAMP stimulation; a G-protein-coupled cAMP receptor and G-proteins are essential for this activation. We have cloned a Dictyostelium gene, DdGCA, encoding a protein with 12 transmembrane spanning regions and two cyclase domains. Sequence alignment demonstrates that the two cyclase domains are transposed, relative to these domains in adenylate cyclases. DdGCA expressed in Dictyostelium exhibits high guanylate cyclase activity and no detectable adenylate cyclase activity. Deletion of the gene indicates that DdGCA is not essential for chemotaxis or osmo-regulation. The knock-out strain still exhibits substantial guanylate cyclase activity, demonstrating that Dictyostelium contains at least one other guanylate cyclase.
腺苷酸环化酶和鸟苷酸环化酶的核心由两个以反平行方式排列的环化酶结构域的分子内或分子间二聚体形成。后生动物膜结合型腺苷酸环化酶由12个跨膜区和两个作为异二聚体起作用并被G蛋白激活的环化酶结构域组成。相比之下，膜结合型鸟苷酸环化酶只有一个跨膜区和一个环化酶结构域，并被细胞外配体激活形成同二聚体。在细胞黏菌盘基网柄菌中，膜结合型鸟苷酸环化酶活性在cAMP刺激后被诱导；一种G蛋白偶联的cAMP受体和G蛋白对于这种激活至关重要。我们克隆了盘基网柄菌的一个基因DdGCA，它编码一种具有12个跨膜区和两个环化酶结构域的蛋白质。序列比对表明，相对于腺苷酸环化酶中的这些结构域，这两个环化酶结构域是转位的。在盘基网柄菌中表达的DdGCA表现出高鸟苷酸环化酶活性，且未检测到腺苷酸环化酶活性。该基因的缺失表明DdGCA对于趋化性或渗透调节并非必不可少。基因敲除菌株仍然表现出大量的鸟苷酸环化酶活性，这表明盘基网柄菌至少还含有另一种鸟苷酸环化酶。
