The Isoelectric Point of Thrombin and its Behaviour Compared to Prothrombin at Some Solid Surfaces

An integrated microfluidic platform for selective and real-time detection of thrombin biomarkers using a graphene FET

Lab-on-a-chip technology offers an ideal platform for low-cost, reliable, and easy-to-use diagnostics of key biomarkers needed for early screening of diseases and other health concerns. In this work, a graphene field-effect transistor (GFET) functionalized with target-binding aptamers is used as a biosensor for the detection of thrombin protein biomarker. Furthermore, this GFET is integrated with a microfluidic device for enhanced sensing performances in terms of detection limit, sensitivity, and continuous monitoring. Under this platform, a picomolar limit of detection was achieved for measuring thrombin; in our experiment measured as low as 2.6 pM. FTIR, Raman and UV-Vis spectroscopy measurements were performed to confirm the device functionalization steps. Based on the concentration-dependent calibration curve, a dissociation constant of KD = 375.8 pM was obtained. Continuous real-time measurements were also conducted under a constant gate voltage (VGS) to observe the transient response of the sensor when analyte was introduced to the device. The target selectivity of the sensor platform was evaluated and confirmed by challenging the GFET biosensor with various concentrations of lysozyme protein. The results suggest that this device technology has the potential to be used as a general diagnostic platform for measuring clinically relevant biomarkers for point-of-care applications.

Laser-induced graphene interdigitated electrodes for label-free or nanolabel-enhanced highly sensitive capacitive aptamer-based biosensors

Highly porous laser-induced graphene (LIG) is easily generated in complex electrode configurations such as interdigitated electrodes (IDEs). Here, we demonstrate that their superior capacitive response at low frequencies can be exploited in affinity biosensors using thrombin aptamers as model biorecognition elements. Of specific interest was the effect of electrode surface area on capacitance detection, and the comparison between a label-free format and enhancement strategies afforded by carboxy group bearing polymeric nanoparticles or liposomes. Electrochemical impedance spectroscopy (EIS) was used to investigate the LIG performance and optimize the biosensor design. Interestingly, the label-free strategy performed extremely well and additional labels decreased the limit of detection or increased the sensitivity only minimally. It is assumed that the highly porous nature of the LIG structures dominates the capacitive response so that labels removed from the surface have only limited influence Also, while slight performance changes can be observed for smaller vs. larger electrode structures, the performance of a LIG IDE is reasonably independent of its size. In the end, a dynamic range of 5 orders of magnitude was obtained (0.01 nM-1000 nM) with a limit of detection as low as 0.12 pM. When measured in serum, this increased to 1.3 pM. The good reproducibility (relative standard deviation (RSD), 4.90%) and repeatability (RSD, 2.59%) and good long-term stability (>7 weeks at 4 °C) prove that a LIG-based capacitance sensor is an excellent choice for affinity-based biosensor. The ease-of-production, the simplicity of modification and the superior performance even in a label-free format indicate that LIG-based biosensors should be considered in point-of-care diagnostics in the future.

Oligonucleotide-based label-free detection with optical microresonators: strategies and challenges

This review targets diversified oligonucleotide-based biodetection techniques, focusing on the use of microresonators of whispering gallery mode (WGM) type as optical biosensors mostly integrated with lab-on-a-chip systems. On-chip and microfluidics combined devices along with optical microresonators provide rapid, robust, reproducible and multiplexed biodetection abilities in considerably small volumes. We present a detailed overview of the studies conducted so far, including biodetection of various oligonucleotide biomarkers as well as deoxyribonucleic acids (DNAs), ribonucleic acids (RNAs) and proteins. We particularly advert to chemical surface modifications for specific and selective biosensing.

From a Laboratory Exercise for Students to a Pioneering Biosensing Technology

Surface plasmon resonance (SPR) for biosensing was demonstrated 30 years ago. In the present contribution, its general background is described together with the necessary developments both in instrumentation and surface chemistry, leading to the final so-called BIAcore technology. The description is naturally colored by my personal opinion of the developments. SPR for the elucidation of organic mono- and multilayers introduced at the end of the 1970s formed the basis for the first biosensing demonstration of SPR in the beginning of the 1980s. It is pointed out how the need of an up-to-date laboratory exercise for the undergraduate students and the multidisciplinary environment at the Laboratory of Applied Physics at Linköping University led to this demonstration. The initial experiments are touched upon and the further developments at Pharmacia, which led to the BIAcore technology, are described in some details. Some of the present activities in Linköping related to optical biosensing with ubiquitous instrumentation are also described, including SPR detection with a computer screen and a web camera and most recently with a cellular phone.

Synthesis and characterization of recombinant factor VIIa-conjugated magnetic iron oxide nanoparticles for hemophilia treatment

Maghemite (gamma-Fe(2)O(3)) nanoparticles of 15.0 +/- 2.1 nm in diameter were prepared by nucleation, followed by controlled growth of magnetic iron oxide thin films onto gelatin nuclei. Functionalization of these magnetic nanoparticles with activated double bonds was accomplished by interacting divinyl sulfone with the gelatin coating of the gamma-Fe(2)O(3) nanoparticles. The activated double bonds were then used for covalent binding, via Michael addition reaction, of recombinant factor VIIa and human serum albumin to the surface of these nanoparticles. Recombinant factor VIIa was also physically bound to the magnetic nanoparticles by interacting this factor with the human serum albumin conjugated gamma-Fe(2)O(3) nanoparticles. The influence of factor VIIa concentration on the immobilization yield has been elucidated. Leakage of the bound factor VIIa into PBS containing 4% albumin was insignificant. The coagulant activity of the physically adsorbed recombinant factor VIIa was similar to that of the free one and was significantly better than that of the covalently bound. The blood half-life of free factor VIIa is short, about 2-3 h, because of digestion by proteolytic enzymes and inhibitory effects. Stabilization of factor VIIa against trypsin (a model proteolytic enzyme) and chloromethyl ketone-type inhibitor was accomplished by conjugation of the factor to the gamma-Fe(2)O(3) nanoparticles. This stabilization may extend the blood half-life of factor VIIa. Therefore, IV injection of factor VIIa conjugated gamma-Fe(2)O(3) nanoparticles instead of free factor may avoid the frequent dosing and reduce the cost of hemophilia treatment.

Effect of the immobilisation of DNA aptamers on the detection of thrombin by means of surface plasmon resonance

We report a multichannel surface plasmon resonance (SPR) sensor for detection of thrombin via DNA aptamers immobilized on the SPR sensor surface. A detailed investigation of the effect of the immobilisation method on the interaction between thrombin and DNA aptamers is presented. Three basic approaches to the immobilisation of aptamers on the surface of the SPR sensor are examined: (i) immobilisation based on chemisorption of aptamers modified with SH groups, (ii) immobilisation of biotin-tagged aptamers via previously immobilized avidin, neutravidin or streptavidin molecular linkers, and (iii) immobilisation employing dendrimers as a support layer for subsequent immobilisation of aptamers. A level of nonspecific binding of thrombin to immobilized human serum albumin (HSA) for each of the immobilisation methods is determined. Immobilisation of aptamers by means of the streptavidin-biotin system yields the best results both in terms of sensor specificity and sensitivity.

Influence of ionic strength, pH and aptamer configuration for binding affinity to thrombin

We used the methods of electrochemical indicators and the quartz crystal microbalance (QCM) for detection of thrombin-aptamer interactions. We analyzed how the method of immobilization of aptamer to a solid support, the aptamer configuration as well as variation in ionic strength and pH will affect the binding of thrombin to the aptamer. The immobilization of aptamer by means of avidin-biotin technology revealed best results in sensitivity in comparison with immobilization utilizing dendrimers of first generation and in comparison with chemisorption of aptamer to a gold surface. Linear and molecular beacon aptamers of similar structure of binding site revealed similar binding properties to thrombin. Increased concentration of NaCl resulted in weakening of the binding of thrombin to the aptamers, probably due to shielding effect of Na(+) ions. The binding of the thrombin to the aptamer depends on electrolyte pH, which is presumably connected with maintaining the three dimensional aptamer configuration, optimal for binding the protein.

Large-scale preparation of human thrombin: polyethylene glycol potentiates the factor Xa-mediated activation of prothrombin

We investigated the ability of polyethylene glycol 4000 to accelerate thrombin generation in a mixture of prothrombin and factor X at concentrations of 1-30%. In the presence of 5 mM of CaCl2, polyethylene glycol 4000 promoted prothrombin activation at concentrations above 1%. The peak of activation was seen at levels of 14 and 20% of polyethylene glycol 4000. The effect of the polyethylene glycol was remarkably dependent on its molecular weight; molecular weights greater than 2000 were required for accelerating thrombin generation. Under optimal conditions, polyethylene glycol 4000, in the presence of CaCl2, promoted conversion of all of the prothrombin into thrombin and its derivatives. We conclude that polyethylene glycol 4000, at concentrations ranging from 14 to 20%, effectively accelerates thrombin generation in the presence of 5 mM of CaCl2. This new method for preparing thrombin is based on the use of polyethylene glycol 4000 and CaCl2 and is applicable to the manufacture of thrombin.

A player of many parts: the spotlight falls on thrombin's structure

The wealth of structural information now available for thrombin, its precursors, its substrates, and its inhibitors allows a rationalization of its many roles. alpha-thrombin is a rather rigid molecule, binding to its target molecules with little conformational change. Comparison of alpha-thrombin with related trypsin-like serine proteinases reveals an unusually deep and narrow active site cleft, formed by loop insertions characteristic of thrombin. This canyon structure is one of the prime causes for the narrow specificity of thrombin. The observed modularity of thrombin allows a diversity in this specificity; its "mix-and-match" nature is exemplified by its interactions with macromolecules (Fig. 20). The apposition of the active site to a hydrophobic pocket (the apolar binding site) on one side and a basic patch (the fibrinogen recognition exosite) on the other allows for a fine tuning of enzymatic activity, as seen for fibrinogen. Thrombin receptor appears to use the same sites, but in a different way. Protein C seems only able to interact with thrombin if the recognition exosite is occupied by thrombomodulin. These two sites are also optimally used by hirudin, allowing the very tight binding observed; thrombin inhibition is effected by blocking access to the active site. On the other hand, antithrombin III makes little use of the recognition exosite; instead, its interactions are tightened with the help of heparin, which binds to a second basic site (the heparin binding site). Thrombin's modularity is a result of the conjunction of amino acid residues of like properties, such as charge or hydrophobicity. The charge distribution plays a role, not only in the binding of oppositely charged moieties of interacting molecules, but also in selection and preorientation of them. Nonproteolytic cellular properties are attributed to 1) the rigid insertion loop at Tyr60A, and 2) a partially inaccessible RGD sequence. The former can interact with cells in the native form; the latter would appear to be presented only in an (at least partially) unfolded state. The membrane binding properties of prothrombin can be understood from the ordered arrangement of calcium ions on binding to the Gla domain. Kringle F2 binds to thrombin at the heparin binding site through charge complementarity; a conformational change appears to occur on binding. The observed rigidity of the thrombin molecule in its complexes makes thrombin ideal for structure based drug design. Thrombin can be inhibited either at the active site or at the fibrinogen recognition exosite, or both.(ABSTRACT TRUNCATED AT 400 WORDS)

The refined 1.9-A X-ray crystal structure of D-Phe-Pro-Arg chloromethylketone-inhibited human alpha-thrombin: structure analysis, overall structure, electrostatic properties, detailed active-site geometry, and structure-function relationships

Thrombin is a multifunctional serine proteinase that plays a key role in coagulation while exhibiting several other key cellular bioregulatory functions. The X-ray crystal structure of human alpha-thrombin was determined in its complex with the specific thrombin inhibitor D-Phe-Pro-Arg chloromethylketone (PPACK) using Patterson search methods and a search model derived from trypsinlike proteinases of known spatial structure (Bode, W., Mayr, I., Baumann, U., Huber, R., Stone, S.R., & Hofsteenge, J., 1989, EMBO J. 8, 3467-3475). The crystallographic refinement of the PPACK-thrombin model has now been completed at an R value of 0.156 (8 to 1.92 A); in particular, the amino- and the carboxy-termini of the thrombin A-chain are now defined and all side-chain atoms localized; only proline 37 was found to be in a cis-peptidyl conformation. The thrombin B-chain exhibits the characteristic polypeptide fold of trypsinlike serine proteinases; 195 residues occupy topologically equivalent positions with residues in bovine trypsin and 190 with those in bovine chymotrypsin with a root-mean-square (r.m.s.) deviation of 0.8 A for their alpha-carbon atoms. Most of the inserted residues constitute novel surface loops. A chymotrypsinogen numbering is suggested for thrombin based on the topological equivalences. The thrombin A-chain is arranged in a boomeranglike shape against the B-chain globule opposite to the active site; it resembles somewhat the propeptide of chymotrypsin(ogen) and is similarly not involved in substrate and inhibitor binding. Thrombin possesses an exceptionally large proportion of charged residues. The negatively and positively charged residues are not distributed uniformly over the whole molecule, but are clustered to form a sandwichlike electrostatic potential; in particular, two extended patches of mainly positively charged residues occur close to the carboxy-terminal B-chain helix (forming the presumed heparin-binding site) and on the surface of loop segment 70-80 (the fibrin[ogen] secondary binding exosite), respectively; the negatively charged residues are more clustered in the ringlike region between both poles, particularly around the active site. Several of the charged residues are involved in salt bridges; most are on the surface, but 10 charged protein groups form completely buried salt bridges and clusters. These electrostatic interactions play a particularly important role in the intrachain stabilization of the A-chain, in the coherence between the A- and the B-chain, and in the surface structure of the fibrin(ogen) secondary binding exosite (loop segment 67-80).(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of NaC1 on inactivation of bovine thrombin by antithrombin III in the presence of low affinity-heparin or dextran sulfate

Heparin with low affinity (LA-heparin) to antithrombin III (AT III) enhanced the rate of inactivation of thrombin by AT III. The enhancement of the rate was saturable with AT III and was proportional to the LA-heparin concentration. Although the rate-enhancement in the presence of LA-heparin decreased with increase in NaC1 concentration, it was comparable with that in the presence of high affinity-heparin (HA-heparin) in the absence of NaC1. Inactivation of thrombin by AT III in the presence of dextran sulfate (DS) was also sensitive to NaC1 concentration. These findings indicate that free AT III is favorable for binding to the complexes of thrombin and highly sulfated polysaccharides having low affinities to AT III in the absence of NaC1.

A method for preparation of dry thrombin for topical application

Thrombin for topical hemostasis can be prepared from bovine or human blood plasma. The prothrombin is isolated by means of adsorption on DEAE-Sephadex A-50 and consecutively activated by CaCl2 and thromboplastin. Thrombin is precipitated and purified by acetone. The specific activity of the thrombin preparation is 122 + 23 IU/mg protein while the yield is 36,360 +/- 6623 IU/liter plasma.

In vivo attempt to consume antithrombin III by i.v. injection of a thrombin-heparin mixture

15 rabbits and 6 dogs were injected with a mixture of thrombin and heparin. Increasing amounts of thrombin, and various ratio of thrombin in relation to heparin, were used. It was found that huge amounts of thrombin could be perfused, under the protection of heparin, without untoward effects. But the high amount of thrombin needed to obtain a 50% reduction of the circulating AT III required a corresponding high amount of protective heparin. Since the secondary injection of protamin sulphate (after the end of the perfusion with the thrombin-heparin mixture) was precipitating the DIC syndrome, such attempts to decrease AT III in man are not feasible.

Effect of glycosaminoglycans and antithrombin III on uptake and inhibition of thrombin by the vascular wall

Thrombin binds to and is inactivated by the endothelium. The inactivation is potentiated by plasma. The present investigation was designed to clarify the role of vessel wall glycosaminoglycans (GAG) and plasma antithrombin III (AT III) in the inactivation and binding of thrombin by endothelium. Thrombin was shown to bind to vascular endothelium and artificial surfaces containing GAG:s. The binding could be inhibited on both types of surfaces by pretreating them with protamine. Thrombin bound to endothelium was rapidly inactivated in the presence of plasma but only slowly if the plasma was replaced by AT III, AT III-depleted plasma or a balanced salt solution. It is concluded that thrombin binds to vessel wall GAG:s and is inactivated by the endothelium. Potentiation of the inhibition of the endothelially bound thrombin by plasma is dependent upon presence of AT III but an additional plasma factor is also required.

The action of thrombin on peptide p-nitroanilide substrates. Substrate selectivity and examination of hydrolysis under different reaction conditions

Kinetic parameters for the action of bovine alpha-thrombin on 24 commercially available peptide p-nitroanilides have been determined. The selectivity constant, kcat/Km, ranges from 3.3 X 10(1) to 1.1 X 10(8) M-1 X S-1 for the poorest and the best substrates, respectively. The best substrates for thrombin were identified as those with arginine in the P1 position, proline or a proline homolog in the P2 position, and an apolar amino acid in the P3 position. Quantitative distinction between lysine and arginine in the P1 position and other amino acids in the P2-P4 positions of the substrate is reported from the changes in the kinetic parameters for substrates differing in only a single amino acid in these positions. Effects of NaCl, CaCl2 and poly(ethylene glycol) concentrations, pH and temperature on the action of thrombin on selected substrates have been assessed. A source of large systematic error in thrombin concentration estimates was identified as resulting from adsorption losses. These losses were eliminated by inclusion of poly(ethylene glycol) in dilution and reaction buffers.

Ellipsometric studies of film formation on tooth enamel and hydrophilic silicon surfaces

The uptake of salivary substances onto hydrophilic negatively charged surfaces of silicon or onto enamel surfaces was studied in vitro with ellipsometry. There was a rapid initial uptake of substances followed by a slow but continuous uptake probably of other substances, which could be removed from saliva by absorption with a S. mutans serotype c strain. the kinetics for the uptake onto enamel and silicon surfaces and the thicknesses of the layers were similar. The combination of ellipsometry and silicon surfaces is suggested as a model for obtaining increased information on dental pellicle formation.