Complement Component 8g (C8g)

The eighth component of complement (C8) consists of 3 nonidentical subunits arranged asymmetrically as a disulfide-linked alpha-gamma dimer and a noncovalently associated beta chain. Genetic studies of C8 polymorphisms established that alpha-gamma and beta are encoded at different loci. Implicit in this finding was the existence of 2 different genes and the likelihood that alpha-gamma is synthesized as a single-chain precursor.

The C8G belong to the lipocalin superfamily, a group of distantly related and similarly folded proteins that are able to carry small lipophilic molecules such as retinol, odorants, and steroids. The lipocalin superfamily has a very ancient origin since lipocalins are found in arthropods as well as in vertebrates.