Patients with leukocyte adhesion molecule (CD11/CD18, β2 integrins) deficiency have structural defects in the common β subunit (CD18), which prevent heterodimer formation and normal cell surface expression of these receptors, leading to life-threatening bacterial infections. To elucidate the nature of these defects in a patient with partial (type II) deficiency, abnormal CD18 cDNA clones were isolated, using the polymerase chain reaction to amplify the patient's B cell-derived cDNAs. Sequence analysis revealed two mutant alleles. cDNA clones, representing a maternal allele, contained both a 12-base pair insertion resulting in an in-frame addition of four amino acids between P247 and E248 and a C1756 →T nucleotide transition, resulting in an R586 → W substitution in the normal CD18 protein. The inframe insertion arose by a single nucleotide C→A transversion in the 3' terminus of an intron, generating an aberrant splice acceptor site. Other cDNA clones contained an A1052 →G nucleotide transition not present in either parent which resulted in an N351 → S substitution. To determine the functional importance of these changes, cDNA encoding a normal α chain (CD11b) was cotransfected into COS with CD18 cDNAs encoding for wild-type, maternal mutant allele, or CD18 containing N351→S substitution. Immunostaining of transfectants with anti-CD18 monoclonal antibodies revealed no cell surface expression of the maternal mutant CD18, and 22% surface expression of N351→S CD18. Both the insertion and the N351→S mutations occurred in a 250 amino acid extracellular region of CD18 that is highly conserved among β integrins supporting a role for this region in heterodimer formation.
|Original language||English (US)|
|Number of pages||7|
|Journal||Journal of Biological Chemistry|
|State||Published - Jan 1 1992|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology