Suzuki S, Naitoh Y
Department of Ophthalmology, University of Southern California School of Medicine, Los Angeles 90038.
EMBO J. 1990 Mar;9(3):757-63. doi: 10.1002/j.1460-2075.1990.tb08170.x.
Using the polymerase chain reaction, we have isolated cDNA clones that encode a new integrin beta subunit--beta 4. Its cDNA, which is 5676 bp in length, has one long coding sequence (5256 bp), a polyadenylation signal and a poly(A) tail. The deduced sequence of 1752 amino acids is unique among the integrin beta subunits. It contains a putative signal sequence as well as a transmembrane domain that divides the molecule into an extracellular domain at the N-terminal side and a cytoplasmic domain at the C-terminal side. The extracellular domain exhibits a 4-fold repeat of cysteine-rich motif similar to those of other integrin beta subunits. Certain features of the extracellular domain, however, are unique to the beta 4 subunit sequence. Of the 56 conserved cysteine residues found within the extracellular domain of other mature beta subunits, eight such residues are deleted from the beta 4 subunit sequence. The cytoplasmic domain is much larger (approximately 1000 amino acids) than those of other beta subunits (approximately 50 amino acids) and has no significant homology with them. A protein homology search revealed that the beta 4 subunit cytoplasmic domain has four repeating units that are homologous to the type III repetition exhibited by fibronectin. The beta 4 subunit mRNA was expressed primarily in epithelial cells. The restricted expression and the new structural features distinguish the integrin beta 4 subunit from other integrin beta subunits.
利用聚合酶链反应，我们分离出了编码一种新的整合素β亚基——β4的cDNA克隆。其cDNA长度为5676 bp，有一个长编码序列（5256 bp）、一个聚腺苷酸化信号和一个聚（A）尾。推导的1752个氨基酸序列在整合素β亚基中是独特的。它包含一个推定的信号序列以及一个跨膜结构域，该结构域将分子分为N端侧的细胞外结构域和C端侧的细胞质结构域。细胞外结构域呈现出与其他整合素β亚基相似的富含半胱氨酸基序的4倍重复。然而，细胞外结构域的某些特征是β4亚基序列所特有的。在其他成熟β亚基的细胞外结构域中发现的56个保守半胱氨酸残基中，有8个这样的残基从β4亚基序列中缺失。细胞质结构域比其他β亚基的细胞质结构域大得多（约1000个氨基酸），且与它们没有明显的同源性。蛋白质同源性搜索显示，β4亚基细胞质结构域有四个与纤连蛋白III型重复序列同源的重复单元。β4亚基mRNA主要在上皮细胞中表达。这种受限的表达和新的结构特征使整合素β4亚基与其他整合素β亚基区分开来。
