Fushiki Daisuke, Hamada Yasuo, Yoshimura Ryoichi, Endo Yasuhisa
Department of Applied Biology, Kyoto Institute of Technology, Kyoto, Japan.
Biomed Res. 2010 Apr;31(2):133-42. doi: 10.2220/biomedres.31.133.
All multi-cellular animals, including hydra, insects and vertebrates, develop gap junctions, which communicate directly with neighboring cells. Gap junctions consist of protein families called connexins in vertebrates and innexins in invertebrates. Connexins and innexins have no homology in their amino acid sequence, but both are thought to have some similar characteristics, such as a tetra-membrane-spanning structure, formation of a channel by hexamer, and transmission of small molecules (e.g. ions) to neighboring cells. Pannexins were recently identified as a homolog of innexins in vertebrate genomes. Although pannexins are thought to share the function of intercellular communication with connexins and innexins, there is little information about the relationship among these three protein families of gap junctions. We phylgenetically and bioinformatically examined these protein families and other tetra-membrane-spanning proteins using a database and three analytical softwares. The clades formed by pannexin families do not belong to the species classification but do to paralogs of each member of pannexins. Amino acid sequences of pannexins are closely related to those of innexins but less to those of connexins. These data suggest that innexins and pannexins have a common origin, but the relationship between innexins/pannexins and connexins is as slight as that of other tetra-membrane-spanning members.
所有多细胞动物，包括水螅、昆虫和脊椎动物，都会形成间隙连接，间隙连接可与相邻细胞直接进行通讯。在脊椎动物中，间隙连接由称为连接蛋白的蛋白质家族组成，而在无脊椎动物中则由内向连接蛋白组成。连接蛋白和内向连接蛋白在氨基酸序列上没有同源性，但两者都被认为具有一些相似的特征，例如四跨膜结构、由六聚体形成通道以及将小分子（如离子）传递到相邻细胞。最近，泛连接蛋白被鉴定为脊椎动物基因组中内向连接蛋白的同源物。尽管泛连接蛋白被认为与连接蛋白和内向连接蛋白共享细胞间通讯功能，但关于间隙连接的这三个蛋白质家族之间的关系，目前所知甚少。我们使用一个数据库和三个分析软件，从系统发育和生物信息学角度对这些蛋白质家族以及其他四跨膜蛋白进行了研究。泛连接蛋白家族形成的进化枝不属于物种分类，而是属于泛连接蛋白每个成员的旁系同源物。泛连接蛋白的氨基酸序列与内向连接蛋白的密切相关，但与连接蛋白的关系较弱。这些数据表明，内向连接蛋白和泛连接蛋白有共同的起源，但内向连接蛋白/泛连接蛋白与连接蛋白之间的关系，与其他四跨膜成员的关系一样微弱。
