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Human complement factor H: molecular cloning and cDNA expression reveals variability in the factor H-related mRNA
W Schwaeble1, E Feifel, C Estaller
1Institut für Hygiene, Innsbruck, Austria.
Abstract:
Previously, we have shown that three different mRNA species of 4.3 kb, 1.8 kb and 1.4 kb, related to human complement factor H, are constitutively expressed in the human liver. Probing with our cDNA clone H-46 which represents 920 bp of the 3' end of the 4.3 kb mRNA of factor H on human liver RNA, we always detected the 4.3 kb and the additional, abundantly expressed mRNA species of 1.4 kb in length, indicating that the 1.4 kb transcript is highly homologous to the 3' end of the classical factor H mRNA of 4.3 kb. Using H-46 as a probe, several cDNA clones were isolated from a liver cDNA library and sequenced. The open reading frame of the novel mRNA species encodes a peptide consisting of five internal short consensus repeat motifs (SCR), identifying the translational product to be a member of the SCR family. Sequence comparison with cDNA clones derived from liver RNA of a different donor provided evidence for variability in the factor H related proteins encoded by the 1.4 kb mRNA species. Interestingly, this variability was found to be restricted to the three carboxyterminal SCR domains. Expression data indicate that our variant is not recognized by the monoclonal antibody 3D11.
Insights
Researchers identified a novel 1.4 kb mRNA species related to human complement factor H. This transcript encodes a protein with short consensus repeat motifs and exhibits variability in its carboxyterminal domains.
Area of Science:
- Molecular Biology
- Immunology
Background:
- Three human complement factor H-related mRNA species (4.3 kb, 1.8 kb, 1.4 kb) are constitutively expressed in the liver.
- A 1.4 kb mRNA species is highly homologous to the 3' end of the classical 4.3 kb factor H mRNA.
Purpose of the Study:
- To characterize the novel 1.4 kb mRNA species related to human complement factor H.
- To investigate the protein product encoded by the 1.4 kb transcript and its variability.
Main Methods:
- Probing human liver RNA with a cDNA clone (H-46) representing the 3' end of the 4.3 kb factor H mRNA.
- Isolation and sequencing of cDNA clones from a liver cDNA library using H-46 as a probe.
- Sequence comparison of cDNA clones from different liver RNA donors.
Main Results:
- The 1.4 kb mRNA encodes a peptide with five short consensus repeat (SCR) motifs, identifying it as a member of the SCR protein family.
- Sequence analysis revealed variability in the factor H-related proteins encoded by the 1.4 kb mRNA, specifically within the carboxyterminal SCR domains.
- Expression data indicated that this variant is not recognized by the monoclonal antibody 3D11.
Conclusions:
- A novel, variable factor H-related protein, encoded by a 1.4 kb mRNA, is expressed in the human liver.
- The identified protein variant belongs to the short consensus repeat (SCR) protein family.
- This variant exhibits distinct immunological properties, as evidenced by its lack of recognition by monoclonal antibody 3D11.