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Strong associations between RFLP and protein polymorphisms for CD46
A N Wilton1, R W Johnstone, I F McKenzie
1School of Biological Sciences, Macquarie University, NSW, Australia.
Abstract:
Human CD46 (membrane cofactor protein) is a cell surface glycoprotein with cofactor activity for the factor I mediated cleavage of components C3b and C4b. Using a CD46 cDNA clone, three restriction enzymes give simple two allele restriction fragment length polymorphisms (RFLPs) in samples of over 300 Caucasians. For Pvu II, P1 with a 16.5 kilobase (kb) fragment and P2 with 14.8 kb + 1.9 kb fragments have frequencies of .40 and .60. For Hin dIII, H1 with a 4.3 kb fragment and H2 with a 2.3 kb fragment have similar frequencies. For Bgl. II, B1 with a 10 kb fragment and B2 with 8.3 kb + 1.8 kb fragments have frequencies of 0.08 and 0.92. There is strong linkage disequilibrium between these polymorphic sites. Designating haplotypes by Hin dIII, Pvu II, Bgl II alleles, there are two common haplotypes P2, H2, B2 and P1, H1, B2, expected at frequencies of .6 and .32, one less common haplotype P1, H1, B1 expected at a frequency .08. The two major protein isoforms of CD46, as detected on peripheral blood lymphocytes by western blot, of Mr 66,000 (alpha) and 56,000 (beta) are determined by differential splicing in production of the mRNA. A strong association between protein isoform and RFLP haplotypes in 30 unrelated subjects suggests that the splicing preference site is in linkage disequilibrium with the RFLPs. The results are consistent with haplotypes P2, H2, B2 and P1, H1, B1 producing predominantly alpha; P1, H1, B2 producing predominantly beta in about 72% of cases and alpha in 28% of cases.
Insights
Researchers identified genetic variations in human CD46 (membrane cofactor protein) using restriction fragment length polymorphisms (RFLPs). These RFLPs are strongly associated with CD46 protein isoforms, suggesting a link between genetic makeup and protein expression.
Area of Science:
- Immunogenetics
- Molecular Biology
- Human Genetics
Background:
- Human CD46 (membrane cofactor protein) is a cell surface glycoprotein involved in complement regulation.
- CD46 plays a role in the factor I-mediated cleavage of C3b and C4b components.
- Understanding CD46 genetic variations is crucial for its role in immune responses.
Purpose of the Study:
- To investigate restriction fragment length polymorphisms (RFLPs) in human CD46.
- To determine the association between CD46 RFLPs and its major protein isoforms.
- To explore linkage disequilibrium between polymorphic sites and splicing preferences.
Main Methods:
- Utilized a CD46 cDNA clone to analyze RFLPs in over 300 Caucasians using Pvu II, Hin dIII, and Bgl. II restriction enzymes.
- Determined CD46 protein isoforms (alpha and beta) via western blot on peripheral blood lymphocytes.
- Analyzed the association between identified RFLP haplotypes and protein isoforms in 30 unrelated subjects.
Main Results:
- Identified two-allele RFLPs for Pvu II, Hin dIII, and Bgl. II with distinct allele frequencies.
- Observed strong linkage disequilibrium between these polymorphic sites, defining common haplotypes (e.g., P2, H2, B2; P1, H1, B2).
- Found a significant association between specific RFLP haplotypes and the predominant expression of CD46 alpha or beta protein isoforms.
Conclusions:
- Human CD46 exhibits genetic polymorphism detectable by RFLPs.
- These RFLPs are in linkage disequilibrium with sites influencing CD46 mRNA splicing.
- The study suggests a genetic basis for the differential expression of CD46 protein isoforms.