Moyle M, Napier M A, McLean J W
Department of Cardiovascular Research, Genentech, Inc., South San Francisco, California 94080.
J Biol Chem. 1991 Oct 15;266(29):19650-8.
Rabbit and human cDNA clones have been identified that encode a novel integrin beta subunit. The sequences that encode this subunit, which has been designated as beta 8, were isolated initially from rabbit placental cDNA libraries using an oligonucleotide probe derived from a highly conserved region of integrin beta subunit sequences. The rabbit clone was used to isolate human beta 8 cDNA clones from human placental and MG-63 osteosarcoma cell libraries. The putative beta 8 polypeptides, which comprise 769 and 768 residues in human and rabbit, respectively, show a high degree of inter-species conservation (approximately 90% identity). In contrast, beta 8 is distinct from the other integrin beta subunits. At the amino acid level human beta 8 ranges from 31 to 37% identity with human beta 1-7. The domain structure of beta 8 is typical of the integrin beta subunits. Human beta 8 has a 42-residue N-terminal signal peptide, a large extracellular domain (approximately 639 residues) that contains four cysteine-rich repeats, a transmembrane domain (approximately 30 residues), and a C-terminal cytoplasmic domain (approximately 58 residues). There are several structural features that are unique to the beta 8 polypeptide, as compared with the other integrin beta subunits. Six of the 56 cysteine residues that are conserved within the extracellular domains of beta 1, beta 2, beta 3, beta 5, beta 6, and the beta subunit from Drosophila are absent in the beta 8 polypeptide. Also, the cytoplasmic domain of the beta 8 subunit shares no homology with the cytoplasmic regions of any of the other integrin beta subunits. Northern analysis demonstrated an approximately 8-kilobase beta 8 mRNA in rabbit placenta, kidney, brain, ovary, and uterus. PCR analysis revealed that beta 8 mRNA is also present in several transformed human cell lines. The beta 8 polypeptide has been transiently expressed in 293 human embryonic kidney cells. A polyclonal antipeptide antibody specific for beta 8 and a polyclonal antibody that recognizes alpha v epitopes were used to show that beta 8 can complex with the endogenous alpha v subunit in 293 cells and that the resulting integrin is expressed as a cell surface complex.
已鉴定出编码一种新型整合素β亚基的兔和人cDNA克隆。编码该亚基（已命名为β8）的序列最初是使用源自整合素β亚基序列高度保守区域的寡核苷酸探针，从兔胎盘cDNA文库中分离出来的。该兔克隆用于从人胎盘和MG - 63骨肉瘤细胞文库中分离人β8 cDNA克隆。推测的β8多肽在人和兔中分别包含769和768个残基，显示出高度的种间保守性（约90%的同一性）。相比之下，β8与其他整合素β亚基不同。在氨基酸水平上，人β8与人β1 - 7的同一性在31%至37%之间。β8的结构域结构是整合素β亚基的典型结构。人β8有一个42个残基的N端信号肽、一个大的细胞外结构域（约639个残基），其中包含四个富含半胱氨酸的重复序列、一个跨膜结构域（约30个残基）和一个C端细胞质结构域（约58个残基）。与其他整合素β亚基相比，β8多肽有几个独特的结构特征。在β1、β2、β3、β5、β6以及果蝇的β亚基的细胞外结构域中保守的56个半胱氨酸残基中，有6个在β8多肽中不存在。此外，β8亚基的细胞质结构域与任何其他整合素β亚基的细胞质区域均无同源性。Northern分析显示兔胎盘组织、肾、脑、卵巢和子宫中有一条约8千碱基的β8 mRNA。PCR分析表明β8 mRNA也存在于几种转化的人细胞系中。β8多肽已在293人胚肾细胞中瞬时表达。使用针对β8的多克隆抗肽抗体和识别αv表位的多克隆抗体，证明β8可以与293细胞中的内源性αv亚基形成复合物，并且产生的整合素作为细胞表面复合物表达。
