MOLECULAR-BASIS OF THE COMPLEMENT-C7 M N-POLYMORPHISM - A NEUTRAL AMINO-ACID SUBSTITUTION OUTSIDE THE EPITOPE OF THE ALLOSPECIFIC MONOCLONAL-ANTIBODY WU-4-15/
R. Wurzner et al., MOLECULAR-BASIS OF THE COMPLEMENT-C7 M N-POLYMORPHISM - A NEUTRAL AMINO-ACID SUBSTITUTION OUTSIDE THE EPITOPE OF THE ALLOSPECIFIC MONOCLONAL-ANTIBODY WU-4-15/, The Journal of immunology, 154(9), 1995, pp. 4813-4819
The allotypes of the C7 M/N polymorphism are determined by comparing t
he ELISA reaction pattern of the allospecific mAb WU 4-15 with polyclo
nal anti-C7 IgG. To characterize the molecular basis of this polymorph
ism, the WU 4-15 epitope was mapped by expression of cDNA fragments. I
t was found to be located within the boundary region of the two short
consensus repeats of C7 (amino acid residues 595-612). Coincidentally
an A or C substitution was found in the course of investigation of the
gene structure at nucleotide 1759. This leads to an electrically neut
ral Pro/Thr substitution at residue 565 and alternative Sau961 or Rsal
restriction sites, respectively. Enzymatic digestion or sequencing of
PCR-amplified genomic DNA from C7 M/N-typed individuals showed a perf
ect correspondence of the genotype with the phenotype of the C7 M/N po
lymorphism. In contrast, no association was found with the genotypes o
f a second polymorphic site at residue 367. Thus, a threonine at amino
acid residue 565 allows access of WU 4-15 to its epitope but its subs
titution with proline almost completely inhibits access in the native
molecule, although the epitope is about 40 amino acid residues distant
from the polymorphic site in the primary structure. Furthermore, the
different conformational structure is probably responsible for the hyp
omorphic appearance of C7N.