Molecular basis of complement C3 deficiency in guinea pigs.

HS Auerbach, R Burger, A Dodds… - The Journal of clinical …, 1990 - Am Soc Clin Investig
HS Auerbach, R Burger, A Dodds, HR Colten
The Journal of clinical investigation, 1990Am Soc Clin Investig
In experiments to ascertain the biochemical basis of a genetically determined deficiency of
the third component of complement (C3) in guinea pigs, we found that C3-deficient liver and
peritoneal macrophages contain C3 messenger RNA of normal size (approximately 5 kb)
and amounts, that this mRNA programs synthesis of pro-C3 in oocytes primed with liver RNA
and in primary macrophage cultures. In each instance, heterodimeric native C3 protein was
secreted with normal kinetics but the C3 protein product of the deficient cells failed to …
In experiments to ascertain the biochemical basis of a genetically determined deficiency of the third component of complement (C3) in guinea pigs, we found that C3-deficient liver and peritoneal macrophages contain C3 messenger RNA of normal size (approximately 5 kb) and amounts, that this mRNA programs synthesis of pro-C3 in oocytes primed with liver RNA and in primary macrophage cultures. In each instance, heterodimeric native C3 protein was secreted with normal kinetics but the C3 protein product of the deficient cells failed to undergo autolytic cleavage and was unusually susceptible to proteolysis. These data and a selective failure of C3 in plasma of deficient animals to incorporate [14C]methylamine suggested either a mutation in primary structure of the C3 protein or a selective defect in co- or postsynthetic processing affecting the thiolester bridge, a structure important for C3 function. A mutation in the primary structure of C3 was ruled out by comparison of direct sequence analysis of C3 cDNA generated from two C3 deficient and two C3 sufficient guinea pig liver libraries. Three base pair differences, none resulting in derived amino acid sequence differences were identified. Finally, restriction fragment length polymorphisms were identified in the C3 gene that are independent of the deficiency phenotype. This marker of the C3 gene permits testing of these hypotheses using molecular biological and classical genetic methods.
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