A staphylococcal GGDEF domain protein regulates biofilm formation independently of cyclic dimeric GMP
A staphylococcal GGDEF domain protein regulates biofilm formation independently of cyclic dimeric GMP
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DOI：
10.1128/jb.00375-08
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发表时间：
2008-08-01
影响因子：
3.2
通讯作者：
O'Gara, James P.
中科院分区：
文献类型：
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作者：
Holland, Linda M.;O'Donnell, Sinead T.;O'Gara, James P.
环二聚GMP（c-di-GMP）是重要的生物膜调节剂，其变构激活胞外多糖生物合成的酶。变形菌基因组通常编码负责c-di-GMP合成的多个含有GGDEF结构域的二鸟苷酸环化酶。相比之下，在测序的葡萄球菌基因组中仅存在一种保守的GGDEF结构域蛋白GdpS（来自葡萄球菌的GGDEF结构域蛋白）和具有高度修饰的GGDEF结构域的第二种蛋白GdpP。在这里，我们研究了GdpS在表皮葡萄球菌生物膜形成中的作用。失活gdpS受损的生物膜形成在培养基中补充NaCl在静态和流动细胞条件下，而gdpS过表达补充突变和增强野生型生物膜的发展。GdpS通过升高icaADBC mRNA水平增加icaADBC编码的胞外多糖聚-N-乙酰葡糖胺的产生。出乎意料的是，发现c-di-GMP合成与GdpS提高icaADBC表达的能力无关。二鸟苷酸环化酶活性所必需的GGEEF基序的突变没有损害GdpS，并且缺乏GGDEF结构域的GdpS的N-末端片段部分地补充了gdpS突变。此外，异源二鸟苷酸环化酶的反式表达未能补充的gdpS突变，并从GdpS纯化的GGDEF结构域在体外没有二鸟苷酸环化酶活性。金黄色葡萄球菌gdpS基因具有与S. epidermidis直系同源物，表明GdpS介导的信号转导在葡萄球菌中是保守的。因此，GdpS通过一种新的c-di-GMP-独立的机制影响生物膜形成，该机制涉及增加icaADBC mRNA水平和胞外多糖生物合成。我们的数据提高了葡萄球菌不能合成c-di-GMP，只有残余的c-di-GMP信号通路的可能性。
Cyclic dimeric GMP (c-di-GMP) is an important biofilm regulator that allosterically activates enzymes of exopolysaccharide biosynthesis. Proteobacterial genomes usually encode multiple GGDEF domain-containing diguanylate cyclases responsible for c-di-GMP synthesis. In contrast, only one conserved GGDEF domain protein, GdpS (for GGDEF domain protein from Staphylococcus), and a second protein with a highly modified GGDEF domain, GdpP, are present in the sequenced staphylococcal genomes. Here, we investigated the role of GdpS in biofilm formation in Staphylococcus epidermidis. Inactivation of gdpS impaired biofilm formation in medium supplemented with NaCl under static and flow-cell conditions, whereas gdpS overexpression complemented the mutation and enhanced wild-type biofilm development. GdpS increased production of the icaADBC-encoded exopolysaccharide, poly-N-acetyl-glucosamine, by elevating icaADBC mRNA levels. Unexpectedly, c-di-GMP synthesis was found to be irrelevant for the ability of GdpS to elevate icaADBC expression. Mutagenesis of the GGEEF motif essential for diguanylate cyclase activity did not impair GdpS, and the N-terminal fragment of GdpS lacking the GGDEF domain partially complemented the gdpS mutation. Furthermore, heterologous diguanylate cyclases expressed in trans failed to complement the gdpS mutation, and the purified GGDEF domain from GdpS possessed no diguanylate cyclase activity in vitro. The gdpS gene from Staphylococcus aureus exhibited similar characteristics to its S. epidermidis ortholog, suggesting that the GdpS-mediated signal transduction is conserved in staphylococci. Therefore, GdpS affects biofilm formation through a novel c-di-GMP-independent mechanism involving increased icaADBC mRNA levels and exopolysaccharide biosynthesis. Our data raise the possibility that staphylococci cannot synthesize c-di-GMP and have only remnants of a c-di-GMP signaling pathway.