Identification of a partial cDNA clone for the C3d/Epstein-Barr virus receptor of human B lymphocytes: homology with the receptor for fragments C3b and C4b of the third and fourth components of complement.

Abstract

Human complement receptor type 2 (CR2) is the B-lymphocyte receptor both for the C3d fragment of the third component of complement and for the Epstein-Barr virus. Amino acid sequence analysis of tryptic peptides of CR2 revealed a strong degree of homology with the human C3b/C4b receptor, CR1. This homology suggested that CR1 gene sequences could be used to detect the CR2 sequences at conditions of low-stringency hybridization. Upon screening a human tonsillar cDNA library with CR1 cDNA sequences, two clones were identified that hybridized at low, but not at high, stringency. Redundant oligonucleotides specific for CR2 sequences were synthesized and used to establish that the two cDNA clones weakly hybridizing with the CR1 cDNA contained CR2 sequences. One of these CR2 cDNA clones hybridized to oligonucleotides derived from two distinct CR2 tryptic peptides, whereas the other, smaller cDNA clone hybridized to oligonucleotides derived from only one of the CR2 peptides. Nucleotide sequence analysis of the CR2 cDNA confirmed that the site of oligonucleotide hybridization was identical to that predicted from the peptide sequence, including flanking sequences not included within the oligonucleotide probes. The CR2-specific cDNA sequences identified a poly(A)+ RNA species of 5 kilobases in RNA extracted from human B cells but did not hybridize to any RNA obtained from the CR2-negative T-cell line HSB-2, thus confirming the appropriate size and tissue-specific distribution for the CR2 mRNA. The striking peptide sequence homology between CR2 and CR1 and the cross-hybridization of the CR2 cDNA with the CR1-specific sequences allow the placement of CR2 in a recently defmed gene family of C3-and C4-binding proteins consisting of CR1, C4-binding protein, factor H, and now, CR2.The C3d/Epstein-Barr virus (EBV) receptor (complement receptor type 2, CR2) of human B lymphocytes is a Mr 145,000 glycoprotein (1-3) comprised of a single polypeptide of Mr 110,000 and 8-11 N-linked oligosaccharides (4). It is expressed by B lymphocytes (5, 6) and follicular dendritic cells of the spleen (7). CR2 recognizes the d region of the C3 component of complement (5, 6) and also serves as the membrane receptor for the human herpesvirus EBV (8, 9), which induces polyclonal activation and immortalization of B lymphocytes and is associated with Burkitt lymphoma and nasopharyngeal carcinoma. CR2 may have a role in physiologic B-cell activation (10, 11) and is phosphorylated when B cells are treated with phorbol 12-myristate 13-acetate or antibody to surface immunoglobulin (12).The recent purification of CR2 permitted the demonstration (13) of significant similarities between its amino acid composition and that of three other proteins of the complement system: factor H, C4-binding protein, and the C3b receptor (complement receptor type 1, CR1). Factor H and C4-binding protein are plasma proteins and CR1 is a membrane glycoprotein found on erythrocytes, most leukocytes, and glomerular podocytes (14). These proteins share certain functions, s...

Molecular cloning of the cDNA encoding the Epstein-Barr virus/C3d receptor (complement receptor type 2) of human B lymphocytes.

“…1A, the XAll insert hybridized to a single 4.7-kb mRNA species from the Raji B cell line but did not recognize mRNA from the human T-cell-derived HSB-2 cell line. These results are in agreement with the reported size of CR2 mRNA (5 kb) derived from tonsil B cells and with the absence of detectable CR2 RNA in the HSB-2 cell line (14).…”

“…A cDNA library was constructed in Xgtll (Stratagene, San Diego, CA) as previously described (17) The cDNA library was initially probed with a 32P-kinase labeled 39-mer oligonucleotide probe (14). High-density screening was done by hybridization on replicative nitrocellulose filters as described (18,19).…”

“…A previous study (14) reported the isolation of a partial CR2 cDNA clone and indicated that CR2 is highly similar to CR1, the C3b/C4b receptor; however, relatively limited nucleotide and protein sequence information was presented in that publication. The genes encoding both CR1 and CR2 have been mapped to human chromosome 1, band q32 (15).…”

CD19 Can Regulate B Lymphocyte Signal Transduction Independent of Complement Activation

“…CD21 is composed of an extracellular domain containing 15 or 16 repeating structural elements termed short consensus repeats (SCRs), a transmembrane region, and a 34-aa cytoplasmic domain (23,24). CD21 and CD35 (complement receptor 1) are alternative splice products of the same Cr2 gene in mice, but are encoded by different genes in humans (25,26).…”

Mapping of the C3d Ligand Binding Site on Complement Receptor 2 (CR2/CD21) Using Nuclear Magnetic Resonance and Chemical Shift Analysis

“…Complement receptor 2 (CR2, CD21) is a 145-kDa Type I transmembrane protein composed of 15 or 16 short consensus repeat (SCR) 2 domains, a 28-amino acid transmembrane domain, and a short 34-amino acid intracellular tail (1)(2)(3)(4)(5). Human CR2 is a cell surface receptor that plays an integral role in the immune system (6 -9).…”