Factor VII Deficiency Caused by a Structural Variant N57D of the First Epidermal Growth Factor Domain

Identification of two novel mutations in three children with congenital factor VII deficiency

Congenital factor VII deficiency (FVIID) is a rare F7 gene mutation causing bleeding disorder inherited in an autosomal recessive manner. In this study, we aimed to identify genetic defects and analyze their relationships with phenotype in three Chinese FVIID patients. The diagnosis of FVIID was made based on FVII coagulant activity (FVII:C) levels assessed through prothrombin time assay. Direct sequencing and protein modeling were performed to detect genetic mutations and the resulting protein expression. Patient 1, a 2-year-old girl, presented with mild bleeding and was found to have a FVII:C of 0.2% and a compound heterozygous F7 Cys389Gly/Cys115Arg mutation. Patient 2, a 7-year-old boy, consulted for moderate bleeding and was found to have a FVII:C of 0.8% and a compound heterozygous F7 Thr241Asn/Pro324Leu mutation. Patient 3, a 5-year-old boy who developed a mild bleeding after trauma was found to have a FVII:C of 1.8% and a compound heterozygous F7 Thr241Asn/ IVS5-2A>G mutation. We hereby report three congenital FVIID patients with FVII:C less than 2% and their respective F7 mutations, two of which (F7 Cys115Arg, Pro324Leu) are novel. The molecular model analysis of the two novel mutations F7 Cys115Arg and Pro324Leu respectively indicated impairment of the proper folding of epidermal growth factor 1 domain situated on F7 gene and impairment of the procoagulant function of FVII both leading to the congenital deficiency of FVII.

A clinical-pathogenetic approach on associated anomalies and chromosomal defects supports novel candidate critical regions and genes for gastroschisis

BACKGROUND

Gastroschisis has been assumed to have a low rate of syndromic and primary malformations. We aimed to systematically review and explore the frequency and type of malformations/chromosomal syndromes and to identify significant biological/genetic roles in gastroschisis.

METHODS

Population-based, gastroschisis-associated anomalies/chromosomal defects published 1950-2018 (PubMed/MEDLINE) were independently searched by two reviewers. Associated anomalies/chromosomal defects and selected clinical characteristics were subdivided and pooled by race, system/region, isolated, and associated cases (descriptive analysis and chi-square test were performed). Critical regions/genes from representative chromosomal syndromes including an enrichment analysis using Gene Ontology Consortium/Panther Classification System databases were explored. Fisher's exact test with False Discovery Rate multiple test correction was performed.

RESULTS

Sixty-eight articles and 18525 cases as a base were identified (prevalence of 17.9 and 3% for associated anomalies/chromosomal defects, respectively). There were 3596 associated anomalies, prevailing those cardiovascular (23.3%) and digestive (20.3%). Co-occurring anomalies were associated with male, female, American Indian, Caucasian, prenatally diagnosed, chromosomal defects, and mortality (P < 0.00001). Gene clusters on 21q22.11 and 21q22.3 (KRTAP), 18q21.33 (SERPINB), 18q22.1 (CDH7, CDH19), 13q12.3 (FLT1), 13q22.1 (KLF5), 13q22.3 (EDNRB), and 13q34 (COL4A1, COL4A2, F7, F10) were significantly related to biological processes: blood pressure regulation and/or vessel integrity, angiogenesis, coagulation, cell-cell and/or cell-matrix adhesion, dermis integrity, and wound healing (P < 0.05).

CONCLUSIONS

Our findings suggest that gastroschisis may result from the interaction of several chromosomal regions in an additive manner as a pool of candidate genes were identified from critical regions supporting a role for vascular disruption, thrombosis, and mesodermal deficiency in the pathogenesis of gastroschisis.

Biological functions of fucose in mammals

Fucose is a 6-deoxy hexose in the l-configuration found in a large variety of different organisms. In mammals, fucose is incorporated into N-glycans, O-glycans and glycolipids by 13 fucosyltransferases, all of which utilize the nucleotide-charged form, GDP-fucose, to modify targets. Three of the fucosyltransferases, FUT8, FUT12/POFUT1 and FUT13/POFUT2, are essential for proper development in mice. Fucose modifications have also been implicated in many other biological functions including immunity and cancer. Congenital mutations of a Golgi apparatus localized GDP-fucose transporter causes leukocyte adhesion deficiency type II, which results in severe developmental and immune deficiencies, highlighting the important role fucose plays in these processes. Additionally, changes in levels of fucosylated proteins have proven as useful tools for determining cancer diagnosis and prognosis. Chemically modified fucose analogs can be used to alter many of these fucose dependent processes or as tools to better understand them. In this review, we summarize the known roles of fucose in mammalian physiology and pathophysiology. Additionally, we discuss recent therapeutic advances for cancer and other diseases that are a direct result of our improved understanding of the role that fucose plays in these systems.

Interspecies exchange mutagenesis of the first epidermal growth factor-like domain of human factor VII

The first epidermal growth factor-like (EGF1) domain of human factor VII (FVII) is essential for binding to tissue factor (TF). We hypothesized that the previously observed increased coagulant activity of rabbit plasma (i.e. FVII) with human TF might be explained by the five non-conserved amino acids in the rabbit vs. the human FVII EGF1 domain. Accordingly, we 'rabbitized' the human FVII EGF1 domain either by exchanging the entire EGF1 domain creating human FVII(rabEGF1) or by the single amino acid substitutions S53N, K62E, P74A, A75D and T83K. After transient expression in HEK293 cells, the recombinant FVII (rFVII) mutant proteins were analyzed for biological activity and binding affinity to human TF by competitive enzyme-linked immunosorbent assay (ELISA). Biological activity of the unpurified rFVII mutant proteins was either depressed or statistically unchanged vs. rFVII(WT). However, three of six rFVII mutant proteins had increased affinity for human TF in the rank order rFVII(rabEGF1) (3.3-fold) > rFVII(K62E) (2.9-fold) > rFVII(A75D) (1.7-fold). The mutant protein rFVII(K62E) was then permanently expressed and purified. Fully activated, purified rFVIIa(K62E) had a twofold greater clotting activity and 2.8-fold greater direct FVIIa amidolytic activity when compared with rFVIIa(WT). Quantitation of the affinity of TF binding by surface plasmon resonance indicated that the KD of purified rFVII(K62E) for human soluble TF (sTF) was 1.5 nM compared with 7.5 nM for rFVII(WT), i.e. fivefold greater affinity. We conclude that substitution of selected amino acid residues of the FVII EGF1 domain facilitated the creation of human rFVII chimeric proteins with both enhanced biological activity and increased affinity for TF.

The significance of published polymorphisms in 14 cases of mild factor VII deficiency

Factor VII (FVII) plays a critical role in the initiation of blood coagulation, and patients with dysfunctional or reduced levels of this protein are susceptible to mucosal bleeding. There is poor correlation between the clinical presentation and the phenotypic data; and in cases of a mild bleeding tendency, mild to moderate reductions in both FVII antigen and activity may be overlooked. The prevalence of FVII deficiency may therefore be underestimated. Polymorphic differences throughout the FVII gene are associated with variations in plasma FVII antigen and activity levels. This study highlights the significance of mild FVII deficiency, and examines the importance of seven previously published polymorphisms in such patients.

Factor VII deficiency and the FVII mutation database

Factor VII (FVII) is a zymogen for a vitamin K-dependent serine protease essential for the initiation of blood coagulation. It is synthesized primarily in the liver and circulates in plasma at a concentration of approximately 0.5 microg/ml (10 nmol/L). The FVII gene (F7) is located on chromosome 13 (13q34), consists of 9 exons, and spans approximately 12kb. It encodes a mature protein of 406 amino acids, which has an N-terminal domain (Gla) post-translationally modified by gamma-carboxylation of glutamic acid residues, two domains with homology to epidermal growth factor (EGF1 and 2), and a C-terminal serine protease domain. The single chain zymogen is activated by proteolytic cleavage at Arg152-Ile153. There are 238 individuals described in the world literature with mutations in their F7 genes (FVII mutation database; europium.csc. mrc.ac.uk). Complete absence of FVII activity in plasma is usually incompatible with life, and individuals die shortly after birth due to severe hemorrhage. The majority of individuals with mutations in their F7 gene(s), however, are either asymptomatic or the clinical phenotype is unknown. In general, a severe bleeding phenotype is only observed in individuals homozygous for a mutation in their F7 genes with FVII activities (FVII:C) below 2% of normal, however, a considerable proportion of individuals with a mild-moderate bleeding phenotype have similar FVII:C by in vitro assay. The failure of in vitro tests to differentiate between these groups may be due to lack of sensitivity in the assays to the very low amounts of FVII:C, which are sufficient to initiate coagulation in vivo. A number of polymorphisms have been identified in the F7 gene and some have been shown to influence plasma FVII antigen levels.

Analysis of the genotypes and phenotypes of 37 unrelated patients with inherited factor VII deficiency

Severe inherited factor VII (FVII) deficiency is a rare autosomal recessive disorder with a poor relationship between FVII coagulant activity and bleeding tendency. Both clinical expression and mutational spectrum are highly variable. We have screened for mutations the FVII gene of 37 unrelated patients with a FVII coagulant activity less than 5% of normal pooled plasmas. The nine exons with boundaries and the 5' flanking region of the FVII gene were explored using a combination of denaturing gradient gel electrophoresis and direct DNA sequencing. This strategy allowed us to characterise 68 out of the 74 predicted FVII mutated alleles. They corresponded to a large panel of 40 different mutations. Among these, 18 were not already reported. Genotypes of the severely affected patients comprised, on both alleles, deleterious mutations which appeared to be related to a total absence of activated FVII. We suggest that this absence of functional FVII can explain the severe clinical expression. Whether a small release of FVII is sufficient to initiate the coagulation cascade and to prevent the expression of a severe phenotype, requires further investigations.

Activation and active site occupation alter conformation in the region of the first epidermal growth factor-like domain of human factor VII

The first epidermal growth factor-like domain (EGF-1) of factor VII (FVII) provides the region of greatest contact during the interaction of FVIIa with tissue factor. To understand this interaction better, the conformation-sensitive FVII EGF-1-specific monoclonal antibody (mAb) 231-7 was used to investigate the conformational effects occurring in this region upon both FVII activation and active site occupation. The binding affinity of mAb 231-7 was approximately 3-fold greater for the zymogen state than for the active state; a result affected by the presence of both calcium and the adjacent Gla domain. Once activated, active site inhibition of FVIIa with a variety of chloromethyl ketone inhibitors resulted in a 10-fold range of affinities of FVIIai molecules to mAb 231-7. Gla domain removal eliminated this variation in affinity, suggesting the involvement of a Gla/EGF-1 interaction in this conformational effect. In addition, the binding of mAb 231-7 to FVIIa EGF-1 stimulated the amidolytic activity of free FVIIa. Taken together, these results imply an allosteric interaction between the FVIIa active site and the EGF-1 domain that is sensitive to variation in active site occupant structure. Thus, these present studies indicate that the conformational change associated with FVII activation and active site occupation involves the EGF-1 domain and suggest potential functional consequences of these changes.

Probing the structural changes in the light chain of human coagulation factor VIIa due to tissue factor association

The crystallographic structure of human coagulation factor VIIa/tissue factor complex bound with calcium ions was used to model the solution structure of the light chain of factor VIIa (residues 1-142) in the absence of tissue factor. The Amber force field in conjunction with the particle mesh Ewald summation method to accommodate long-range electrostatic interactions was used in the trajectory calculations. The estimated TF-free solution structure was then compared with the crystal structure of factor VIIa/tissue factor complex to estimate the restructuring of factor VIIa due to tissue factor binding. The solution structure of the light chain of factor VIIa in the absence of tissue factor is predicted to be an extended domain structure similar to that of the tissue factor-bound crystal. Removal of the EGF1-bound calcium ion is shown by simulation to lead to minor structural changes within the EGF1 domain, but also leads to substantial relative reorientation of the Gla and EGF1 domains.

Linear analogues derived from the first EGF-like domain of human blood coagulation factor VII: enhanced inhibition of FVIIa/TF complex activity by backbone modification through aspartimide formation

Coagulation factor VII bound to its cofactor tissue factor is the physiological initiator of blood coagulation. The interaction between factor VII and tissue factor involves all four of the structural modules found in factor VII, with the most significant contribution coming from the first EGF-like domain. In this study, the synthesis and biological activity of several analogues derived from the first EGF-like domain of FVII comprising the sequence 45-83 are reported on. The six cysteine residues found in the native protein were replaced by Abu. The peptides were isolated from a multicomponent mixture following standard Fmoc solid phase synthesis. Purification and characterisation of the heterogeneous product showed that aspartimide formation was a major side-reaction, occurring predominantly at the Asp46-Gly47 and Asn57-Gly58 dipeptides. Although relatively common in peptide synthesis, the extent to which this side-reaction had taken place was considered surprising. Reported herein are the analytical methods used to isolate and characterise several of the modified products. Also, the inhibitory effect of these peptides on the formation and enzymatic activity of the factor VIIa/tissue factor complex have been compared. Surprisingly, the peptide containing an iso-Asp residue at position 57 possessed 66-fold higher inhibitory activity compared with the original target peptide. A possible explanation for this increase in observed activity is presented.

Coagulation factor VII Gln100 --> Arg. Amino acid substitution at the epidermal growth factor 2-protease domain interface results in severely reduced tissue factor binding and procoagulant function

We have used recombinant mammalian expression and purification of the factor VII (FVII) variant Gln100 --> Arg (Q100RFVII) to study FVII deficiency in subjects with this mutation. Q100RFVII was secreted poorly in comparison with wild-type FVII (WTFVII) in a stable mammalian expression system, and purified variant protein was found to have undetectable clotting activity. Following activation by immobilized factor Xa, Q100RFVIIa had amidolytic activity similar to WTFVIIa in the absence of soluble tissue factor (sTF); however, unlike WTFVIIa no typical increase in activity was seen after addition of sTF. In a factor X activation assay using relipidated transmembrane truncated tissue factor (residues 1-243), Q100RFVIIa showed less than 5% of the ability of WTFVIIa to activate factor X. We performed direct binding analysis of WT and Q100RFVII/FVIIa to immobilized sTF using surface plasmon resonance, and severely reduced binding of both non-activated and activated Q100RFVII to sTF was seen, indicating a pronounced defect in tissue factor (TF) interaction with this variant. In the sTF-FVIIa crystal structure the candidate residue Gln100 is not in contact with TF but is at the epidermal growth factor 2-protease domain interface. We suggest that the mutation results in a global fold change severely reducing tissue factor interaction; mutation of FVII residues not directly involved in the interaction with TF may still result in variant FVII unable to take part in the initiation of coagulation.