Vitamin K and the Biosynthesis of Prothrombin

Mini-Review: Electrochemical Sensors Used for the Determination of Water- and Fat-Soluble Vitamins: B, D, K

Vitamins are one of the most essential organic compounds that are necessary for the human body, in order to develop and grow in a healthy way. The aim of this mini-review is to bring together a series of electrochemical sensors (voltametric and amperometric) developed for the determination of vitamins from the families of B, D and K in biological, pharmaceutical or food-related samples. For this mini-review, 16 articles published between 2016 and 2021 were taken into consideration.

Hepatocellular carcinoma in acute hepatic porphyrias: A Damocles Sword

Porphyrias are inherited diseases with low penetrance affecting the heme biosynthesis pathway. Acute intermittent porphyria (AIP), variegate porphyria (VP) and hereditary coproporphyria (HCP) together constitute the acute hepatic porphyrias (AHP). These diseases have been identified as risk factors for primary liver cancers (PLC), mainly hepatocellular carcinoma (HCC: range 87-100%) but also cholangiocarcinoma, alone or combination with HCC. In AHP, HCC annual incidence rates range from 0.16 to 0.35% according to the populations studied. Annual incidence rates are higher in Swedish and Norwegian patients, due to a founder effect. It increases above age 50. The pathophysiology could include both direct toxic effects of heme precursors, particularly δ-aminolevulinic acid (ALA), compound heterozygosity for genes implied in heme biosynthesis pathway or the loss of oxidative stress homeostasis due to a relative lack of heme. The high HCC incidence justifies radiological surveillance in AHP patients above age 50. Efforts are made to find new biological non-invasive markers. In this respect, we describe here the first report of PIVKA-II clinical utility in the follow-up of an AIP patient that develop an HCC. In this manuscript we reviewed the epidemiology, the physiopathology, and the screening strategy of HCC in AHP.

Vitamin K and osteoporosis: Myth or reality?

Vitamin K is a liposoluble vitamin. The predominant dietary form, phylloquinone or vitamin K1, is found in plants and green vegetables; whereas menaquinone, or vitamin K2, is endogenously synthesized by intestinal bacteria and includes several subtypes that differ in side chain length. Aside from its established role in blood clotting, several studies now support a critical function of vitamin K in improving bone health. Vitamin K is in fact required for osteocalcin carboxylation that in turn regulates bone mineral accretion; it seems to promote the transition of osteoblasts to osteocytes and also limits the process of osteoclastogenesis. Several observational and interventional studies have examined the relationship between vitamin K and bone metabolism, but findings are conflicting and unclear. This systematic review aims to investigate the impact of vitamin K (plasma levels, dietary intake, and oral supplementation) on bone health with a particular interest in bone remodeling, mineral density and fragility fractures.

Effect of vitamin K on bone mineral density: a meta-analysis of randomized controlled trials

A number of randomized controlled trials (RCTs) examining the role of vitamin K on bone mineral density (BMD) have yielded inconsistent results. We performed a meta-analysis of these trials to assess the effect of vitamin K on BMD. We searched MEDLINE, EMBASE and CENTRAL for relevant studies of RCTs examining the role of vitamin K on BMD. Data on participants, interventions, and outcomes were extracted and the quality of all included trials assessed. Primary outcomes for analysis were absolute changes in BMD (mg/cm(2)) at the lumbar spine and femoral neck. Relative changes (percentage change) in BMD at the lumbar spine were also assessed. Vitamin K supplementation was shown to be efficacious in increasing BMD at the lumbar spine but not the femoral neck. The weighted mean difference (WMD) in BMD absolute change was 21.60 mg/cm(2) [95% confidence interval (CI) 3.63, 39.56] at the lumbar spine and 0.25 mg/cm(2) (95% CI -2.64, 3.14) at the femoral neck. The WMD in BMD relative change was 1.27% (95% CI 0.47, 2.06) at the lumbar spine and 0.17 (95% CI -0.21, 0.54) at the femoral neck. Subgroup analysis revealed that ethnic difference, gender, and vitamin K type were associated with variable effects on BMD at the lumbar spine. The modest overall treatment effects for vitamin K on BMD observed in this review may be biased and should be interpreted with caution. Further studies are required to address factors relating to the observed effects of vitamin K on BMD.

The vitamin K cycle

Vitamin K is a collective term for lipid-like naphthoquinone derivatives synthesized only in eubacteria and plants and functioning as electron carriers in energy transduction pathways and as free radical scavengers maintaining intracellular redox homeostasis. Paradoxically, vitamin K is a required micronutrient in animals for protein posttranslational modification of some glutamate side chains to gamma-carboxyglutamate. The majority of gamma-carboxylated proteins function in blood coagulation. Vitamin K shuttles reducing equivalents as electrons between two enzymes: VKORC1, which is itself reduced by an unknown ER lumenal reductant in order to reduce vitamin K epoxide (K>O) to the quinone form (KH2); and gamma-glutamyl carboxylase, which catalyzes posttranslational gamma-carboxylation and oxidizes KH2 to K>O. This article reviews vitamin K synthesis and the vitamin K cycle, outlines physiological roles of various vitamin K-dependent, gamma-carboxylated proteins, and summarizes the current understanding of clinical phenotypes caused by genetic mutations affecting both enzymes of the vitamin K cycle.

Computational study of coagulation factor VIIa's affinity for phospholipid membranes

The interaction between the gamma-carboxyglutamic acid-rich domain of coagulation factor VIIa (FVIIa), a vitamin-K-dependent enzyme, and phospholipid membranes plays a major role in initiation of blood coagulation. However, despite a high sequence and structural similarity to the Gla domain of other vitamin-K-dependent enzymes with a high membrane affinity, its affinity for negatively charged phospholipids is poor. A few amino acid differences are responsible for this observation. Based on the X-ray structure of lysophosphatidylserine (lysoPS) bound to the Gla domain of bovine prothrombin (Prth), models of the Gla domain of wildtype FVIIa and mutated FVIIa Gla domains in complex with lysoPS were built. Molecular dynamics (MD) and steered molecular dynamics (SMD) simulations on the complexes were applied to investigate the significant difference in the binding affinity. The MD simulation approach provides a structural and dynamic support to the role of P10Q and K32E mutations in the improvement of the membrane contact. Hence, rotation of the Gly11 main chain generated during the MD simulation results in a hydrogen bond with Q10 side chain as well as the appearance of a hydrogen bond between E32 and Q10 forcing the loop harbouring Arg9 and Arg15 to shrink and thereby enhances the accessibility of the phospholipids to the calcium ions. Furthermore, the application of the SMD simulation method to dissociate C6-lysoPS from a series of Gla domain models exhibits a ranking of the rupture force that can be useful in the interpretation of the PS interaction with Gla domains. Finally, adiabatic mapping of Gla6 residue in FVIIa with or without insertion of Tyr4 confirms the critical role of the insertion on the conformation of the side chain Gla6 in FVIIa and the corresponding Gla7 in Prth.

Models of blood coagulation

Our research aims to provide quantitatively transparent, biologically realistic descriptions of the processes involved in hemostasis which will permit predictions of the behavior of the coagulation system in normal and pathologic states. We use four models of coagulation: (1) numerical approximations of the tissue factor (Tf) pathway of thrombin generation based upon mechanism and dynamics; (2) Tf activation of the "blood coagulation proteome" from isolated cells and proteins; (3) Tf activated contact pathway inhibited whole blood in vitro; and (4) blood shed from standardized microvascular wounds in vivo. The results from these models are integrated in interactive assessments aimed at achieving convergence of biochemical rigor and biological authenticity. Microvascular injury is the most biologically secure but least accessible to mechanistic study. Numerical models while quantitatively transparent are biologically limited. By the integrated analyses of all four models, we establish observations which require inclusion or discovery of new parameters to achieve mechanistically interpretable biological reality. Discoveries made in this fashion have included thrombin's role in the initiation phase, TFPI/ATIII/APC synergy interactions, rfVIIa in fVII deficiency, the roles of fVIII and fIX in the Tf reaction, and the cleavage of fIX by fXa membrane. Ideally, our results will provide descriptions which predict the behavior of the biological blood coagulation system under normal and pathologic conditions.

Mutagenesis of the gamma-carboxyglutamic acid domain of human factor VII to generate maximum enhancement of the membrane contact site

Site-directed mutagenesis of the 40 N-terminal residues (gamma-carboxyglutamic acid domain) of blood clotting factor VII was carried out to identify sites that improve membrane affinity. Improvements and degree of change included P10Q (2-fold), K32E (13-fold), and insertion of Tyr at position 4 (2-fold). Two other beneficial changes, D33F (2-fold) and A34E (1.5-fold), may exert their impact via influence of K32E. The modification D33E (5.2-fold) also resulted in substantial improvement. The combined mutant with highest affinity, (Y4)P10Q/K32E/D33F/A34E, showed 150-296-fold enhancement over wild-type factor VIIa, depending on the assay used. Undercarboxylation of Glu residues at positions 33 and 34 may result in an underestimate of the true contributions of gamma-carboxyglutamic acid at these positions. Except for the Tyr(4) mutant, all other beneficial mutations were located on the same surface of the protein, suggesting a possible membrane contact region. An initial screening assay was developed that provided faithful evaluation of mutants in crude mixtures. Overall, the results suggest features of membrane binding by vitamin K-dependent proteins and provide reagents that may prove useful for research and therapy.

gamma -Glutamyl carboxylation: An extracellular posttranslational modification that antedates the divergence of molluscs, arthropods, and chordates

The posttranslational gamma-carboxylation of glutamate residues in secreted proteins to gamma-carboxyglutamate is carried out by the vitamin K-dependent enzyme gamma-glutamyl carboxylase. gamma-Carboxylation has long been thought to be a biochemical specialization of vertebrates, essential for blood clotting. Recently, a gamma-carboxylase was shown to be expressed in Drosophila, although its function remains undefined in this organism. We have characterized both cDNA and genomic clones for the gamma-glutamyl carboxylase from the marine mollusc, Conus, the only nonvertebrate organism for which gamma-carboxyglutamate-containing proteins have been biochemically and physiologically characterized. The predicted amino acid sequence has a high degree of sequence similarity to the Drosophila and vertebrate enzymes. Although gamma-carboxylases are highly conserved, the Conus and mammalian enzymes have divergent substrate specificity. There are striking parallels in the gene organization of Conus and human gamma-carboxylases. Of the 10 Conus introns identified, 8 are in precisely the same position as the corresponding introns in the human enzyme. This remarkable conservation of intron/exon boundaries reveals that an intron-rich gamma-carboxylase was present early in the evolution of the animal phyla; although specialized adaptations in mammals and molluscs that require this extracellular modification have been identified, the ancestral function(s) and wider biological roles of gamma-carboxylation still need to be defined. The data raise the possibility that most introns in the genes of both mammals and molluscs antedate the divergence of these phyla.

Oral anticoagulation thresholds

BACKGROUND

Monitoring patients on oral anticoagulation is essential to prevent hemorrhage and recurrent thrombosis. We studied tissue factor-induced whole-blood coagulation in patients on warfarin therapy with similar international normalized ratios (INRs).

METHODS AND RESULTS

Contact pathway-suppressed whole-blood coagulation initiated with tissue factor was studied in 8 male subjects (group W) and in 1 individual multiple times (subject A). Coagulation profiles for group W showed that subjects with similar INRs had widely varying clot times (6.2 to 23 minutes) and thrombin-antithrombin III (TAT) profiles with rates of 25 to 40 nmol. L(-1). min(-1) and maximum levels varying from 192 to 349 nmol/L. The normal control group exhibited clot times of 5.7+/-0.3 minutes and TAT rates of 57+/-13 nmol. L(-1). min(-1), reaching maximum levels of 742+/-91 nmol/L. Subject A, who was stably anticoagulated at an INR of 2.1+/-0.4 for 6 months, had widely ranging profiles with clot times of 9.0 to 22.7 minutes, TAT maximums varying from 141 to 345 nmol/L, and TAT formation rates of 10 to 57 nmol. L(-1). min(-1). INR did not correlate with TAT formation. Platelet activation was decreased by anticoagulants but also displayed variability. Fibrinopeptide A generation showed threshold variability independent of the INR. Factor VIII levels were increased (P=0.03) in group W (204+/-34.4%) compared with normal control subjects (149.4+/-37.4%). A significant correlation was identified between increasing factor VIII levels and years on warfarin therapy (r=0.78, P=0.01), suggesting a possible factor VIII compensatory mechanism.

CONCLUSIONS

These results suggest that control of anticoagulation in patients to a set INR therapeutic range may be less secure than anticipated. Patients with similar INRs show significant individual variability in their tissue factor coagulation response, suggesting different risks to anticoagulation when confronted with underlying vascular anomalies.

Identification of two novel transmembrane gamma-carboxyglutamic acid proteins expressed broadly in fetal and adult tissues

The proline-rich gamma-carboxyglutamic acid (Gla) proteins (PRGPs) 1 and 2 are the founding members of a family of vitamin K-dependent single-pass integral membrane proteins characterized by an extracellular amino terminal domain of approximately 45 amino acids that is rich in Gla. The intracellular carboxyl terminal region of these two proteins contains one or two copies of the sequence PPXY, a motif present in a variety of proteins involved in such diverse cellular functions as signal transduction, cell cycle progression, and protein turnover. In this report, we describe the cloning of the cDNAs for two additional human transmembrane Gla proteins (TMG) of 20-24 kDa named TMG3 and TMG4. These two proteins possess extracellular Gla domains with 13 or 9 potential Gla residues, respectively, followed by membrane-spanning hydrophobic regions and cytoplasmic carboxyl terminal regions that contain PPXY motifs. This emerging family of integral membrane Gla proteins includes proline-rich Gla protein (PRGP) 1, PRGP2, TMG3, and TMG4, all of which are characterized by broad and variable distribution in both fetal and adult tissues. Members of this family can be grouped into two subclasses on the basis of their gene organization and amino acid sequence. These observations suggest novel physiological functions for vitamin K beyond its known role in the biosynthesis of proteins involved in blood coagulation and bone development. The identification and characterization of these proteins may allow a more complete understanding of the teratogenic consequences of exposure in utero to vitamin K antagonists, such as warfarin-based anticoagulants.

Vitamin K-dependent proteins

Vitamin K is required for the synthesis of gamma-carboxyglutamate (Gla) during postribosomal protein modification. Substrates include blood clotting proteins, bone proteins, cell signaling, and receptor proteins. In addition, Gla is a component of short toxin peptides from the marine snail Conus. Studies of structure-function relationships are the most advanced for the blood coagulation proteins. Reviews of vitamin K action and blood coagulation are presented. Special focus is on the structure-function role of Gla in blood coagulation and the impact of this amino acid on enzyme reaction kinetics. This amino acid forms calcium and membrane binding sites for these proteins. Two proposed mechanisms of protein-membrane attachment are reviewed. One involves membrane attachment by protein insertion into the hydrocarbon region of the membrane, while another considers attachment by specific interactions with phospholipid head groups. Membrane attachment generates the potential for several forms of nonclassical enzyme kinetic behaviors, all of which have been observed in vitro. For example, the reaction may be limited by properties of the enzyme active site, a condition that allows use of classic steady-state enzyme kinetic parameters. However, the reaction may be limited by substrate binding to the membrane, by substrate flux through solution, and/or by solvent flow rates across the membrane surface. These states provide special mechanisms that are not anticipated by classical steady-state kinetic derivations. They may be used to regulate coagulation in vivo. Overall, vitamin K research spans the spectrum of biological research and experience. Exciting new ideas and findings continue to emanate from vitamin K-related research.

Primary structure and tissue distribution of two novel proline-rich gamma-carboxyglutamic acid proteins

Two human cDNAs that encode novel vitamin K-dependent proteins have been cloned and sequenced. The predicted amino acid sequences suggest that both are single-pass transmembrane proteins with amino-terminal gamma-carboxyglutamic acid-containing domains preceded by the typical propeptide sequences required for posttranslational gamma-carboxylation of glutamic acid residues. The polypeptides, with deduced molecular masses of 23 and 17 kDa, are proline-rich within their putative cytoplasmic domains and contain several copies of the sequences PPXY and PXXP, motifs found in a variety of signaling and cytoskeletal proteins. Accordingly, these two proteins have been called proline-rich Gla proteins (PRGP1 and PRGP2). Unlike the gamma-carboxyglutamic acid domain-containing proteins of the blood coagulation cascade, the two PRGPs are expressed in a variety of extrahepatic tissues, with PRGP1 and PRGP2 most abundantly expressed in the spinal cord and thyroid, respectively, among those tissues tested. Thus, these observations suggest a novel physiological role for these two new members of the vitamin K-dependent family of proteins.

Localization of the factor IX propeptide binding site on recombinant vitamin K dependent carboxylase using benzoylphenylalanine photoaffinity peptide inactivators

The propeptide binding/activation site on the vitamin K dependent carboxylase has been localized to a region of carboxylase between residues Arg +50 and Glu +225 by photoinactivation studies using [125I]tyrosyl-labeled benzoylphenylalanine (Bpa)-containing analogs of proFIX19, a peptide containing residues -18 to +1 of factor IX. Four proFIX19 analogs with Bpa substituents at -16, -13, -7, and -6 were synthesized. These peptides were specific photoinactivators of carboxylase and were used to label a His6-carboxylase construct produced in baculovirus-infected insect cells. Fragments of the labeled carboxylase produced by V8 protease digestion were analyzed by peptide-specific antibodies and by autoradiography. The propeptide recognition site was localized to the N-terminal one-third of the 94 kDa carboxylase. This is consistent with previous studies using a carboxylase substrate affinity label, N-(bromoacetyl)-FLEELY [Kuliopulos, A., Nelson, N.P., Yamada, M., Walsh, C.T., Furie, B., Furie, B.C., & Roth, D.A. (1994) J. Biol. Chem. 269, 21364-21370], indicating that the propeptide binding site and the FLEEL binding site are both located within the N-terminal one-third of the vitamin K dependent carboxylase.

Partially carboxylated prothrombins. II. Effect of gamma-carboxyglutamyl residues on the properties of prothrombin fragment 1

Purified prothrombin fragments 1 derived from normal (10-carboxyglutamyl) and dicoumarol-induced 7-, 5-, 2-, 1-, and 0-carboxyglutamyl prothrombins contained the same number of gamma-carboxyglutamyl residues as their respective parent molecules. The effect of gamma-carboxyglutamyl residues was more pronounced on the fragments 1 than on the prothrombins. Consequently, the pI values of the fragments 1 were very well differentiated, with normal fragment 1 focusing at pH 3.58, 7-carboxyglutamyl fragment 1 at 3.79, 5- at 3.97, and 2- at pH 4.29. Similarly, by agar gel electrophoresis, normal fragment 1 was the most mobile, followed by 7-, 5-, 2-, 1- and lastly 0-carboxyglutamyl fragment 1. Because of Ca2+ being bound to the carboxyglutamyl residues, the electrophoretic mobility of normal fragment 1, in the presence of Ca2+, was reduced the most, followed by 7-, 5- and then 2-carboxyglutamyl fragment 1, while the mobilities of the 1- and 0-carboxyglutamyl fragments 1 were not affected. In contrast to their parent molecules, all of the fragments 1 in the presence of EDTA gave negative immunoprecipitation reactions against antibodies produced against normal prothrombin. In the presence of Ca2+, conversely, the fragments 1 containing comparable amounts of antigenic activity all gave positive reactions. However, the intensity of the immunoprecipitates varied, as normal fragment 1 gave the most prominent immunoprecipitation reaction, consecutively followed by 7-, 5-, 2-, 1- and lastly 0-carboxyglutamyl fragment 1 where the precipitation was so faint that it was hardly visible.

Bovine prothrombin fragment 1, segment 1-10. Synthesis and immunological investigation

The N-terminal decapeptide methyl ester, H-Ala-Asn-Lys-Gly-Phe-Leu-Gla-Gla-Val-Arg-OCH3 (16) of bovine prothrombin fragment 1 has been prepared by standard solution techniques, via a fragment coupling strategy. Hexapeptide Boc-Ala-Asn-Lys epsilon (Boc)-Gly-Phe-Leu-OBzl (9) was obtained by coupling Boc-Ala-Asn-Lys epsilon (Boc)Gly-OH (6) to the trifluoroacetate salt of H-Phe-Leu-OBzl (8). Hydrogenolysis of (9) followed by coupling to HCl. H-Gla gamma (OtBu)2-Gla gamma (OtBu)2-Val-Arg(HCl)-OCH3 (14) gave the fully protected decapeptide (15). Treatment of 15 with 90% trifluoroacetic acid followed by ion exchange chromatography of 15 yielded the methyl ester (16). The decapeptide 16 labeled with 125I using the Bolton-Hunter reagent, did not bind to antibodies specific for the calcium ion-induced conformation of bovine fragment 1.

Mechanism of action of vitamin K: synthesis of gamma-carboxyglutamic acid

Vitamin K (2-methyl-3-phytyl-1,4-naphthoquinone) is required for the synthesis of prothrombin, Factor VII, Factor IX, Factor X, and a number of newly discovered proteins. These plasma proteins participate in calcium-dependent phospholipid membrane interactions which are mediated through the presence of gamma-carboxyglutamyl residues in their amino-terminal region. Vitamin K is required for the postribosomal conversion of glutamyl residues in liver precursors of these proteins to gamma-carboxyglutamyl residues in the completed plasma proteins. In the absence of vitamin K, or in the presence of vitamin K antagonists, animals produce plasma forms which lack the carboxylated residue. These proteins are nonfunctional because of their lack of phospholipid interaction. The vitamin K-dependent carboxylase which carries out this reaction has been studied in rat liver microsomal preparations where it will carboxylate the endogenous precursor proteins. Low-molecular-weight glutamyl-containing peptide substrates, such as Phe-Leu-Glu-Glu-Leu, which are homologous to regions of the prothrombin precursor, will also serve as substrates for the detergent-solubilized enzyme. This enzyme has been shown to require the reduced form of the vitamin and O2 but no ATP or a biotin-containing protein for its activity. The same microsomal preparations will also convert vitamin K to its 2,3-epoxide, and it is possible that activity may be related to the role of the vitamin in driving the carboxylase reaction.

The gamma-carboxy glutamic acid content of human and bovine prothrombin following warfarin treatment

A form of prothrombin induced by Warfarin therapy, has been isolated which is adsorbed onto insoluble barium salts, but has a reduced biological activity. This protein contains, on average, seven out of a possible ten gamma-carboxy glutamic acid residues. A second form of prothrombin is also described, which is not adsorbed into barium slats, and has less than 1% the activity of the normal protein, contains only four gamma-carboxy glutamic acid residues. The significance of these results is discussed.

gamma-Carboxyglutamic acid distribution

The distribution of the vitamin K-dependent amino acid, gamma-carboxyglutamic acid was examined in proteins from a variety of sources. Proteins examined include purified rat and bovine coagulation proteins, barium citrate-adsorbing proteins from trout plasma, lamprey plasma, earthworm hemolymph, army worm hemolymph, lobster hemolymph, E. coli B/5, soybean leaf, the protein lysate from the hemolymph cell of the horseshoe crab and parathyroid extract. Other purified proteins examined included human alpha-1-antitrypsin, pepsinogen, S-100, fetuin, tropomyosin-troponin and complement protein C-3. Of these, only the blood-cotting proteins and the vertebrate plasma samples were shown to contain gamma-carboxyglutamic acid.

Interactions of the components of the prothrombinase complex

The interaction of components of the prothrombinase complex, i.e. bovine Factor X or Factor Xa, bovine Factor V or Factor Va, phospholipid, and Ca2+, in various combinations was studied primarily by a gel filtration technique. In experiments, in which phospholipids ranging from those isolated from naturally occurring sources to those long chain (18 : 1) as well as short chain 6 : 0 and 7 : 0 fatty acids prepared by chemical and enzymatic synthesis were used, it was evident that a net negative surface charge on the lipid dispersions was one of the important requirements for interaction. Though the short chain fatty acid phospholipids interacted with the proteins of the prothrombinase complex, there was invariably a diminution in the activity of the enzyme complex. It was established that Factor V or Va did not bind Ca2+ and that the binding of either of these factors with phospholipids (with a net negative charge) was not dependent on Ca2+. However, the interaction of Factor X or Factor Xa with phospholipids with a negative charge required Ca2+. It was shown that Factor X could bind to the same type of lipid of lipid surface as that noted for Factor Xa. Of interest was the apparent difference in the phospholipid binding characteristics of the two variant forms of bovine plasma Factor X, i.e. X1 and X2, which might in part explain the differences in their specific activities. Of importance was the lack of demonstrable complex formation between Factors II, X and V in the absence of phospholipids and/or in the presence or absence of Ca2+. The significance of these results as they might apply to the configuration of the prothrombinase complex and its interaction with prothrombin plus the usefulness of the short chain fatty acid phospholipid in exploring these lipid-protein interactions are discussed.