Coding and non-coding polymorphisms in the lectin pathway activator L-ficolin gene in 188 Dutch blood bank donors

Abstract number: 1733_1251

Herpers B.L., Immink M.M., de Jong B.A.W., van Velzen-Blad H., de Jongh B.M., van Hannen E.J.

Objective: Human L-ficolin (FCN) is a serum lectin characterised by a collagen-like and a fibrinogen-like domain that can activate the lectin pathway of complement. Structural and functional similarities to mannose-binding lectin (MBL) suggest a role for L-ficolin in innate immunity similar to MBL. Structural polymorphisms in the MBL2 gene, leading to functional deficiency of MBL, have been associated with disease. We screened the coding regions of the FCN2 gene for similar polymorphisms and determined their frequencies in a Dutch population.

Methods: We developed 10 denaturing gradient gel electrophoresis (DGGE) assays to screen a total of 188 Dutch Caucasians for polymorphisms in all exons of FCN2 and their flanking regions. Sequence variations detected with DGGE were confirmed with sequencing.

Results: Total gene screening in this large cohort revealed 10 single nucleotide polymorphisms (SNPs) in the FCN2 gene (table; (a) location and allele names, (b) nucleotide substitutiuon, (c) frequency and allele count). Non-coding SNPs were found in the 5'-UTR and 3'-UTR, in introns 2, 3 and 6 and in exons 3 and 8. Two highly conserved coding SNPs were found in exon 8, leading to amino acid substitutions within the fibrinogen-like domain

Conclusion: A total of ten polymorphisms were identified. Non-coding SNPs were found in the 5'-UTR and the 3'-UTR, in the introns 2, 3 and 6 and in exons 3 and 8. Although such polymorphisms have been described to influence translation or splicing events in other genes, the relevance of these SNPs in this particular gene has to be further investigated.

Three coding SNPs were found in exon 5 and exon 8 encoding the fibrinogen-like domain of L-ficolin. Fibrinogen-like domains are highly conserved throughout several proteins in many species. These domains consists of approximately 220–250 residues with 26 invariant, mostly hydrophobic residues and at least 46 highly conserved residues. The two SNPs found in exon 8 respectively result in the substitution of threonine with the hydrophobic methionine and alanine with serine in the near proximity of several conserved residues.

As the fibrinogen-like domain of L-ficolin is responsible for pattern recognition, it is of interest to investigate whether the genetic variation in this domain alters the affinity or specificity of carbohydrate binding. Such possible influence could affect the recognition of invading microorganisms and thereby influence one of the first lines of defence in innate immunity.

Location, amino acid substitution and frequency of SNPs in FCN2