A single amino acid substitution in a common African allele of the CD4 molecule ablates binding of the monoclonal antibody, OKT4.
The CD4 molecule is a relatively non-polymorphic 55 kDa glycoprotein expressed on a subset of T lymphocytes. A common African allele of CD4 has been identified by non-reactivity with the monoclonal antibody, OKT4. The genetic basis for the OKT4- polymorphism of CD4 is unknown. In the present paper, the structure of the CD4 molecule from an homozygous CD4OKT4- individual was characterized at the molecular level. The size of the CD4OKT4- protein and mRNA were indistinguishable from those of the OKT4+ allele. The polymerase chain reaction (PCR) was used to map the structure of CD4OKT4- cDNAs by amplifying overlapping DNA segments and to obtain partial nucleotide sequence after asymmetric amplification. PCR was then used to clone CD4OKT4- cDNAs spanning the coding region of the entire, mature CD4 protein by amplification of two overlapping segments followed by PCR recombination. The nucleotide sequence of CD4OKT4- cDNA clones revealed a G----A transition at bp 867 encoding an arginine----tryptophan substitution at amino acid 240 relative to CD4OKT4+. Expression of a CD4OKT4- cDNA containing only this transition, confirmed that the arginine----tryptophan substitution at amino acid 240 ablates the binding of the mAb OKT4. A positively charged amino acid residue at this position is found in chimpanzee, rhesus macaque, mouse and rat CD4 suggesting that this mutation may confer unique functional properties to the CD4OKT4- protein.
Lederman
S
S
Department of Medicine, Columbia University, New York, NY 10032.
DeMartino
J A
JA
Daugherty
B L
BL
Foeldvari
I
I
Yellin
M J
MJ
Cleary
A M
AM
Berkowitz
N
N
Lowy
I
I
Braunstein
N S
NS
Mark
G E
GE
D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D001483:Base Sequence; D015704:CD4 Antigens / Q000235:genetics*; D002144:Callithrix; D002460:Cell Line; D002874:Chromosome Mapping; D005434:Flow Cytometry; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D010957:Plasmids; D016133:Polymerase Chain Reaction; D011110:Polymorphism, Genetic; D011233:Precipitin Tests; D012689:Sequence Homology, Nucleic Acid; D014162:Transfection
D000911:Antibodies, Monoclonal; D015704:CD4 Antigens