Mutational analysis of the PRYSPRY domain of pyrin and implications for familial mediterranean fever (FMF)

Dynamic disequilibrium-based pathogenicity model in mutated pyrin’s B30.2 domain—Casp1/p20 complex

Background

The B30.2 variants lead to most relevant severity forms of familial Mediterranean fever (FMF) manifestations. The B30.2 domain plays a key role in protein-protein interaction (PPI) of pyrin with other apoptosis proteins and in regulation the cascade of inflammatory reactions. Pyrin-casp1 interaction is mainly responsible for the dysregulation of the inflammatory responses in FMF. Lower binding affinity was observed between the mutant B30.2 pyrin and casp1 without the release of the complete pathogenicity mechanism. The aim of this study was to identify the possible effects of the interface pocked residues in B30.2/SPRY-Casp1/p20 complex using molecular mechanics simulation and in silico analysis.

Results

It was found that Lys671Met, Ser703Ile, and Ala744Ser variants led mainly to shift of the binding affinity (∆G), dissociation constant (K_d), and root mean square deviation (RMSD) in B30.2/SPRY-Casp1/p20 complex leading to dynamic disequilibrium of the p20-B30.2/SPRY complex toward its complex form. The current pathogenicity model and its predicted implementation in the relevant colchicine dosage were delineated.

Conclusion

The molecular mechanics analysis of B30.2/SPRY-p20 complex harboring Lys671Met, Ser703Ile, and Ala744Ser variants showed dynamic disequilibrium of B30.2/SPRY-casp1/p20complex in context of the studied variants that could be a new computational model for FMF pathogenicity. This study also highlighted the specific biochemical markers that could be useful to adjust the colchicine dose in FMF patients.

The Frequency of MEFV Gene Mutations and Genotypes in Sanliurfa Province, South-Eastern Region of Turkey, after the Syrian Civil War by Using Next Generation Sequencing and Report of a Novel Exon 4 Mutation (I423T)

Background: Familial Mediterranean Fever (FMF) is a genetic disorder characterized by recurrent episodes of fever and abdominal pain. Mutations in the Mediterranean fever (MEFV) gene are localized on the p arm of chromosome 16. Over 333 MEFV sequence variants have been identified so far in FMF patients, which occur mostly in the 2nd and 10th exons of the gene. Methods: In this study, 296 unrelated patients with clinical suspicion of FMF, which were admitted during January–December 2017, were retrospectively reviewed to identify the frequency of MEFV gene mutations by using next generation sequencing. Results: Eighteen different mutations, 45 different genotypes and a novel exon 4 (I423T) mutation were identified in this study. This mutation is the fourth mutation identified in exon 4.The most frequent mutation was R202Q, followed by M694V, E148Q, M680I, R761H, V726A and R354W. Conclusions: One of the most important aims of this study is to investigate the MEFV mutation type and genotype of migrants coming to Sanliurfa after the civil war of Syria. This study also examines the effect of the condition on the region’s gene pool and the distribution of different types of mutations. Our results indicated that MEFV mutations are highly heterogeneous in our patient population, which is consistent with the findings of other studies in our region. Previously used methods, such as Restriction Fragment Length Polymorphism (RFLP), do not define uncommon or especially novel mutations. Therefore, Next Generation Sequencing (NGS) analysis of the MEFV gene could be useful for finding novel mutations, except for those located on exon 2 and 10.

The MEFV gene pathogenic variants and phenotype-genotype correlation in children with familial Mediterranean fever in the Çanakkale population

The aim of the current study was to determine the frequency of the Mediterranean fever (MEFV) gene pathogenic variants in 60 children diagnosed with familial Mediterranean fever (FMF) and to compare the phenotype-genotype correlation. Genomic DNA was isolated by the spin-column method from peripheral blood samples (collected in vacutainers containing EDTA) and buccal smears. The MEFV gene profiles for the current FMF cohort were genotyped by pyrosequencing and direct Sanger sequencing techniques for the target pathogenic variants. The most prominent clinical symptoms were abdominal pain (53.4%), fever (23.4%) and arthritis (23.3%). Eighteen different pathogenic variants were identified and the most frequent were p.Met694Val (20.0%), p.Glu148Gln (13.3%), p.Met680 Ile (11.7%) and p.Arg202Gln (11.7%). Abdominal pain, fever and arthritis were the most common presenting clinical characteristics. Results showed that not only clinical characteristics, but also genotyping of the MEFV gene is needed to establish the correct diagnosis of FMF in children and other family members.

Dysregulated production of interleukin-1β upon activation of the NLRP3 inflammasome in patients with familial Mediterranean fever

Familial Mediterranean fever (FMF) is caused by mutations in pyrin, a protein expressed in innate immune cells that interacts with caspase-1 and other inflammasome components to regulate interleukin (IL)-1β maturation. Since NLRP3 inflammasome represents major source of IL-1β, we studied its protein expression and function in FMF. We isolated peripheral white blood cells (WBCs) from 20 symptoms-free FMF patients and 21 healthy individuals. Intracellular protein expression of NLRP3, caspase-1, IL-1β at baseline and after LPS/ATP sequential treatment for NLRP3 activation was assessed by immunoblotting. Secreted IL-1β was quantified by ELISA. THP-1 cells were transfected with wild-type or mutant pyrin and IL-1β secretion was measured. FMF WBCs exhibited lower NLRP3 and active caspase-1 protein expression compared to healthy individuals, and LPS/ATP treatment resulted in significantly lower intracellular IL-1β levels in FMF patients. Likewise, LPS/ATP induced caspase-1-dependent IL-1β release at significantly lower amounts in the FMF group (1182±192 versus 2134±245pg/mL in controls, p=0.004). Consistently, THP-1 cells transfected with FMF-associated M694V mutant pyrin displayed lower LPS/ATP-induced IL-1β compared with wild-type pyrin-transfected cells. FMF WBCs demonstrate reduced NLRP3-mediated IL-1β production. Additional studies are needed to define whether this finding represents a compensatory mechanism to control inflammation or is directly linked to disease pathogenesis.

Crystal structure of TRIM20 C-terminal coiled-coil/B30.2 fragment: implications for the recognition of higher order oligomers

Many tripartite motif-containing (TRIM) proteins, comprising RING-finger, B-Box, and coiled-coil domains, carry additional B30.2 domains on the C-terminus of the TRIM motif and are considered to be pattern recognition receptors involved in the detection of higher order oligomers (e.g. viral capsid proteins). To investigate the spatial architecture of domains in TRIM proteins we determined the crystal structure of the TRIM20Δ413 fragment at 2.4 Å resolution. This structure comprises the central helical scaffold (CHS) and C-terminal B30.2 domains and reveals an anti-parallel arrangement of CHS domains placing the B-box domains 170 Å apart from each other. Small-angle X-ray scattering confirmed that the linker between CHS and B30.2 domains is flexible in solution. The crystal structure suggests an interaction between the B30.2 domain and an extended stretch in the CHS domain, which involves residues that are mutated in the inherited disease Familial Mediterranean Fever. Dimerization of B30.2 domains by means of the CHS domain is crucial for TRIM20 to bind pro-IL-1β in vitro. To exemplify how TRIM proteins could be involved in binding higher order oligomers we discuss three possible models for the TRIM5α/HIV-1 capsid interaction assuming different conformations of B30.2 domains.

Association analysis of three ABCB1 (MDR1) gene variants (C1236T, G2677A/T and C3435T) and their genotype/haplotype combinations with the familial Mediterranean fever

1. Familial Mediterranean fever (FMF) is considered an autosomal recessive disorder, associated with a single gene named Mediterranean fever (MEFV). The aim of this study was to perform genotyping and haplotyping analysis of the multidrug resistance (ATP-binding cassette, subfamily B, member 1 - ABCB1) gene in FMF patients. 2. Three ABCB1 gene polymorphisms (C1236T, G2677T/A and C3435T) were analyzed in 309 FMF patients and 250 healthy control subjects. All subjects were genotyped by PCR-restriction fragment length polymorphism analysis, and statistical analysis was performed using the Arlequin 3.1.1 and SPSS 16.0 software packages. 3. The CT genotype frequency of the C3435T polymorphism (p = 0.003), the CT-GT-CT (C1236T-G2677T/A-C3435T) triple genotype (p = 0.001) and the C-G (C1236T-G2677T/A) haplotype (p = 0.030) were more common in the FMF patients. The CT-GG-CC triple genotype and T-G-C, C-T-T and T-G-T haplotypes (C1236T-G2677T/A-C3435T) were higher in the control subjects (p = 0.011, 0.001, 0.009 and 0.000, respectively). The CT-GG binary genotype and C-T and T-G haplotypes for C1236T-G2677T/A polymorphisms may have a high degree of protective effect against FMF (p = 0.0005, 0.002 and 0.000, respectively). 4. Our study showed that genotypes and haplotypes of ABCB1 gene polymorphisms may affect patients' FMF susceptibility.

The role of the pro-apoptotic protein Siva in the pathogenesis of Familial Mediterranean fever: A structural and functional analysis

Familial Mediterranean fever (FMF) is an autosomal, recessive disease, attributed to mutations in MEFV gene encoding pyrin, which is characterized by recurrent, acute and self-limiting attacks of fever as well as an increased neutrophil and monocyte apoptosis. Most disease-associated mutations in MEFV gene reside on the C-terminal PRYSPRY (B30.2) domain of pyrin, an area found to interact with the pro-apoptotic protein Siva. Because apoptotic events may be contributing to endogenous inflammation we hypothesized that mutations in pyrin may affect Siva-mediated apoptosis. The confirmation of this hypothesis would be of a great biological significance since it would be demonstrated a connection between apoptosis and inflammation. We used homology modeling to construct a 3-D model of Siva protein and the constructed model of Siva defined structural elements with potential of binding other proteins to induce apoptosis. Given that Siva protein binds pyrin as shown by transfection and immunoprecipitation experiments, apoptosis was assessed by FACS and Western blotting. No differences in rates of apoptosis in myeloid cells (THP-1) upon transfection with either wt pyrin or mutant forms of pyrin were found. Patients with FMF did not display any mutations in the Siva-1 (full length) gene. Siva-1 was not linked to pyrin in the major predicted FMF gene network constructed using a literature-curated gene signature for FMF. These results suggest that Siva-mediated unprovoked apoptosis is not likely to be involved in the pathogenesis of FMF.

The crystal structure of human pyrin b30.2 domain: implications for mutations associated with familial Mediterranean fever

The inherited autoinflammatory syndrome familial Mediterranean fever (FMF) is characterized by recurrent episodes of fever, which are independent of any bacterial or viral infections. This disease is associated with point mutations in the mefv gene product pyrin. Although the precise molecular functions of pyrin are unknown, it seems to be involved in the maturation and secretion of interleukin-1beta. Approximately two thirds of all FMF-associated mutations cluster in the C-terminal B30.2 domain of pyrin. To investigate the molecular consequences of FMF-associated mutations, we determined the crystal structure of the pyrin B30.2 domain at 1.35-A resolution. The comparison with other B30.2/ligand complex structures revealed a shallow cavity, which seems to be involved in binding the pyrin ligand. The bottom of this cavity is covered mainly with hydrophobic amino acids, suggesting that pyrin recognizes its ligand by hydrophobic contacts and surface complementarities. FMF-associated mutations cluster around two sites on the B30.2 surface. Approximately two thirds, including those mutations with the most severe disease outcomes, are observed in the vicinity of the predicted peptide binding site, suggesting that they will have a direct impact on ligand binding. A second mutational hot spot was observed on the opposite side of the B30.2 domain in the neighbourhood of its artificial N-terminus. Although most FMF-associated mutations are solvent exposed, several will modify the main-chain conformation of loops. The experimental crystal structure of the pyrin B30.2 domain serves as a basis for an accurate modelling of these mutations.

Familial Mediterranean Fever: a review for clinical management

Familial Mediterranean Fever (FMF) is a hereditary autosomal recessive, autoinflammatory disorder characterized by recurrent, self-limiting episodes of short duration (mean 24-72 h) of fever and serositis. FMF is the most frequent periodic febrile syndrome among the autoinflammatory syndromes (AS), a heterogeneous group of recently identified diseases clinically characterized by recurrent febrile attacks, in the absence of autoantibodies and antigen-specific T lymphocytes. In FMF, periodic attacks show inter- and intra-individual variability in terms of frequency and severity. Usually, they are triggered by apparently innocuous stimuli and may be preceded by a prodromal period. The Mediterranean FeVer gene (MEFV) responsible gene maps on chromosome 16 (16p13) encoding the pyrin-marenostrin protein. The precise pathologic mechanism is still to be definitively elucidated; however a new macromolecular complex, called inflammasome, seems to play a major role in the control of inflammation and it might be involved in the pathogenesis of FMF. The most severe long-term complication is type AA amyloidosis, principally affecting the kidney and the cause of chronic renal failure. Two types of risk factors, genetic and non-genetic, have been identified for this complication. Currently, the only effective treatment of Familial Mediterranean Fever is the colchicine. New drugs in a few colchicine resistant patients have been tried, but additional studies on larger series are necessary to draw definitive conclusions.

Structural basis for PRYSPRY-mediated tripartite motif (TRIM) protein function

The human tripartite motif (TRIM) family comprises 70 members, including HIV restriction factor TRIM5alpha and disease-associated proteins TRIM20 (pyrin) and TRIM21. TRIM proteins have conserved domain architecture but diverse cellular roles. Here, we describe how the C-terminal PRYSPRY domain mediates diverse TRIM functions. The crystal structure of TRIM21 PRYSPRY in complex with its target IgG Fc reveals a canonical binding interface comprised of two discrete pockets formed by antibody-like variable loops. Alanine scanning of this interface has identified the hot-spot residues that control TRIM21 binding to Fc; the same hot-spots control HIV/murine leukemia virus restriction by TRIM5alpha and mediate severe familial Mediterranean fever in TRIM20/pyrin. Characterization of the IgG binding site for TRIM21 PRYSPRY reveals TRIM21 as a superantigen analogous to bacterial protein A and suggests that an antibody bipolar bridging mechanism may contribute to the pathogenic accumulation of anti-TRIM21 autoantibody immune complex in autoimmune disease.

Pathogenesis of familial periodic fever syndromes or hereditary autoinflammatory syndromes

Familial periodic fever syndromes, otherwise known as hereditary autoinflammatory syndromes, are inherited disorders characterized by recurrent episodes of fever and inflammation. The general hypothesis is that the innate immune response in these patients is wrongly tuned, being either too sensitive to very minor stimuli or turned off too late. The genetic background of the major familial periodic fever syndromes has been unraveled, and through research into the pathophysiology, a clearer picture of the innate immune system is emerging. After an introduction on fever, interleukin-1beta and inflammasomes, which are involved in the majority of these diseases, this manuscript offers a detailed review of the pathophysiology of the cryopyrin-associated periodic syndromes, familial Mediterranean fever, the syndrome of pyogenic arthritis, pyoderma gangrenosum and acne, Blau syndrome, TNF-receptor-associated periodic syndrome and hyper-IgD and periodic fever syndrome. Despite recent major advances, there are still many questions to be answered regarding the pathogenesis of these disorders.