Apparently non-expressed alleles of factor B (BF) code for hypomorphic proteins

Abstract

In three families with an apparent non-expressed factor B (BF) allele (BF*Q0), advanced methods of isoelectric focusing for the determination of BF F subtypes revealed different hypomorphic BF products (BF QL) with functional hemolytic activity expressed by the assumed BF*Q0 allele. A Taq I and a Msp I restriction fragment length polymorphism as well as the Ba fragment of the expression products showed banding patterns for the BF*QL alleles corresponding to BF S types, whereas an altered Bb fragment was seen in two BF QL products. In one family an intragenic recombination site within the Bb part of the BF gene was assumed. Investigations of factor B and its conversion fragments, as demonstrated by the used methods, allow to complement molecular genetic investigations of BF*Q0 alleles in heterozygous genotypes on a protein level. We conclude that apparently non-expressed alleles of factor B code for hypomorphic but functionally active proteins.

Improvement of BF typing and of BF F subtyping after neuraminidase treatment in the unconverted and converted factor B

“…Since BF allotypes are demonstrated without bands cathodic to their major band, BF QL products expressed by the other chromosome can be detected [24] if their respective major band is demonstrated more cathodically. Because of its high sensitivity, immunoblotting following IEF methods demonstrates banding intensity relations which are essential for BF allotyping of S, F and FS types, without the clear distinction possible with direct immunofixation.…”

“…From this it may be concluded that F types, after treatment with neuraminidase, show no structure, which allows focusing at the isoelectric point ofthe major S band. This makes it possible to use this Ba fragment demonstration when the existence of a Ba S in hypomorphic products of factor B is to be clarified [24]. Because of the great differences in the pattern between the FA subtype, which appears with two intensive bands, and the FB subtype after removal of neuraminic acid residues, these proteins could differ-besides differing in amino acid sequences [40] -in a posttranslational addition of a molecular group.…”

“…Hypomorphic products of so-called BF*QO alleles, not detectable by using established methods, are demonstrated in different positions cathodic to the major F band ( Fig. 4; for a detailed description see [24]). The bands characteristic both of types and of subtypes can also be demonstrated by immunoblotting.…”