Arnaout M A, Gupta S K, Pierce M W, Tenen D G
Renal Unit, Children's Hospital, Boston, Massachusetts.
J Cell Biol. 1988 Jun;106(6):2153-8. doi: 10.1083/jcb.106.6.2153.
Mo1 (complement receptor type 3, CR3; CD11b/CD18) is an adhesion-promoting human leukocyte surface membrane heterodimer (alpha subunit 155 kD [CD11b] noncovalently linked to a beta subunit of 95 kD [CD18]). The complete amino acid sequence deduced from cDNA of the human alpha subunit is reported. The protein consists of 1,136 amino acids with a long amino-terminal extracytoplasmic domain, a 26-amino acid hydrophobic transmembrane segment, and a 19-carboxyl-terminal cytoplasmic domain. The extracytoplasmic region has three putative Ca2+-binding domains with good homology and one with weak homology to the "lock washer" Ca2+-binding consensus sequence. These metal-binding domains explain the divalent cation-dependent functions mediated by Mo1. The alpha subunit is highly homologous to the alpha subunit of leukocyte p150,95 and to a lesser extent, to the alpha subunit of other "integrin" receptors such as fibronectin, vitronectin, and platelet IIb/IIIa receptors in humans and position-specific antigen-2 (PS2) in Drosophila. Mo1 alpha, like p150, contains a unique 187-amino acid stretch NH2-terminal to the metal-binding domains. This region could be involved in some of the specific functions mediated by these leukocyte glycoproteins.
Mo1（补体3型受体，CR3；CD11b/CD18）是一种促进黏附的人白细胞表面膜异二聚体（α亚基为155kD[CD11b]，与95kD[CD18]的β亚基非共价连接）。报道了从人α亚基cDNA推导的完整氨基酸序列。该蛋白质由1136个氨基酸组成，具有一个长的氨基末端胞外结构域、一个26个氨基酸的疏水跨膜片段和一个19个羧基末端胞质结构域。胞外区域有三个与“锁紧垫圈”Ca2+结合共有序列具有良好同源性的假定Ca2+结合结构域和一个同源性较弱的结构域。这些金属结合结构域解释了由Mo1介导的二价阳离子依赖性功能。α亚基与白细胞p150,95的α亚基高度同源，在较小程度上与人类其他“整合素”受体（如纤连蛋白、玻连蛋白和血小板IIb/IIIa受体）以及果蝇中的位置特异性抗原-2（PS2）的α亚基同源。与p150一样，Mo1α在金属结合结构域的氨基末端含有一个独特的187个氨基酸的片段。该区域可能参与这些白细胞糖蛋白介导的一些特定功能。
