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.
Amino acid sequence of the alpha subunit of human leukocyte adhesion receptor Mo1 (complement receptor type 3).
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M A Arnaout, S K Gupta, M W Pierce, D G Tenen; Amino acid sequence of the alpha subunit of human leukocyte adhesion receptor Mo1 (complement receptor type 3).. J Cell Biol 1 June 1988; 106 (6): 2153–2158. doi: https://doi.org/10.1083/jcb.106.6.2153
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