Lobley Anna, Pierron Valerie, Reynolds Lindsey, Allen Liz, Michalovich David
Target Discovery, Inpharmatica Ltd, 60 Charlotte Street, London W1T 2NU, UK.
Reprod Biol Endocrinol. 2003 Aug 1;1:53. doi: 10.1186/1477-7827-1-53.
CatSper1 and CatSper2 are two recently identified channel-like proteins, which show sperm specific expression patterns. Through targeted mutagenesis in the mouse, CatSper1 has been shown to be required for fertility, sperm motility and for cAMP induced Ca2+ current in sperm. Both channels resemble a single pore forming repeat from a four repeat voltage dependent Ca2+ /Na+ channel. However, neither CatSper1 or CatSper2 have been shown to function as cation channels when transfected into cells, singly or in conjunction. As the pore forming units of voltage gated cation channels form a tetramer it has been suggested that the known CatSper proteins require additional subunits and/or interaction partners to function.
Using in silico gene identification and prediction techniques, we have identified two further members of the CatSper family, CatSper3 and Catsper4. Each carries a single channel-forming domain with the predicted pore-loop containing the consensus sequence TxDxW. Each of the new CatSper genes has evidence for expression in the testis. Furthermore we identified coiled-coil protein-protein interaction domains in the C-terminal tails of each of the CatSper channels, implying that CatSper channels 1,2,3 and 4 may interact directly or indirectly to form a functional tetramer.
The topological and sequence relationship of CatSper1 and CatSper2 to the four repeat Ca2+ /Na+ channels suggested other members of this family may exist. We have identified a further two novel CatSper genes, conserved in both the human and mouse genomes. Furthermore, all four of the CatSper proteins are predicted to contain a common coiled-coil protein-protein interaction domain in their C-terminal tail. Coupled with expression data this leads to the hypothesis that the CatSper proteins form a functional hetero-tetrameric channel in sperm.
CatSper1和CatSper2是最近鉴定出的两种通道样蛋白，呈现精子特异性表达模式。通过对小鼠进行靶向诱变，已证明CatSper1是生育能力、精子活力以及精子中cAMP诱导的Ca2+电流所必需的。这两种通道都类似于四重复电压依赖性Ca2+/Na+通道中的单个孔形成重复序列。然而，当单独或联合转染到细胞中时，CatSper1和CatSper2均未显示出作为阳离子通道的功能。由于电压门控阳离子通道的孔形成单位形成四聚体，因此有人提出已知的CatSper蛋白需要额外的亚基和/或相互作用伙伴才能发挥功能。
利用计算机基因鉴定和预测技术，我们又鉴定出了CatSper家族的另外两个成员，即CatSper3和CatSper4。每个成员都带有一个单一的通道形成结构域，预测的孔环包含共有序列TxDxW。每个新的CatSper基因都有在睾丸中表达的证据。此外，我们在每个CatSper通道的C末端尾部鉴定出了卷曲螺旋蛋白-蛋白相互作用结构域，这意味着CatSper通道1、2、3和4可能直接或间接相互作用形成功能性四聚体。
CatSper1和CatSper2与四重复Ca2+/Na+通道的拓扑和序列关系表明该家族可能存在其他成员。我们又鉴定出了另外两个新的CatSper基因，它们在人类和小鼠基因组中均保守。此外，预计所有四种CatSper蛋白在其C末端尾部都含有一个共同的卷曲螺旋蛋白-蛋白相互作用结构域。结合表达数据，这导致了一个假设，即CatSper蛋白在精子中形成功能性异源四聚体通道。
