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The Plasma Factor XIII Heterotetrameric Complex Structure: Unexpected Unequal Pairing within a Symmetric Complex. Biomolecules 2019; 9:biom9120765. [PMID: 31766577 PMCID: PMC6995596 DOI: 10.3390/biom9120765] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Revised: 11/15/2019] [Accepted: 11/19/2019] [Indexed: 02/07/2023] Open
Abstract
Factor XIII (FXIII) is a predominant determinant of clot stability, strength, and composition. Plasma FXIII circulates as a pro-transglutaminase with two catalytic A subunits and two carrier-protective B subunits in a heterotetramer (FXIII-A2B2). FXIII-A2 and -B2 subunits are synthesized separately and then assembled in plasma. Following proteolytic activation by thrombin and calcium-mediated dissociation of the B subunits, activated FXIII (FXIIIa) covalently cross links fibrin, promoting clot stability. The zymogen and active states of the FXIII-A subunits have been structurally characterized; however, the structure of FXIII-B subunits and the FXIII-A2B2 complex have remained elusive. Using integrative hybrid approaches including atomic force microscopy, cross-linking mass spectrometry, and computational approaches, we have constructed the first all-atom model of the FXIII-A2B2 complex. We also used molecular dynamics simulations in combination with isothermal titration calorimetry to characterize FXIII-A2B2 assembly, activation, and dissociation. Our data reveal unequal pairing of individual subunit monomers in an otherwise symmetric complex, and suggest this unusual structure is critical for both assembly and activation of this complex. Our findings enhance understanding of mechanisms associating FXIII-A2B2 mutations with disease and have important implications for the rational design of molecules to alter FXIII assembly or activity to reduce bleeding and thrombotic complications.
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Hethershaw EL, Adamson PJ, Smith KA, Goldsberry WN, Pease RJ, Radford SE, Grant PJ, Ariëns RAS, Maurer MC, Philippou H. The role of β-barrels 1 and 2 in the enzymatic activity of factor XIII A-subunit. J Thromb Haemost 2018; 16:1391-1401. [PMID: 29675848 PMCID: PMC6175083 DOI: 10.1111/jth.14128] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2017] [Indexed: 01/04/2023]
Abstract
Essentials The roles of β-barrels 1 and 2 in factor XIII (FXIII) are currently unknown. FXIII truncations lacking β-barrel 2, both β-barrels, or full length FXIII, were made. Removing β-barrel 2 caused total loss of activity, removing both β-barrels returned 30% activity. β-barrel 2 is necessary for exposure of the active site cysteine during activation. SUMMARY Background Factor XIII is composed of an activation peptide segment, a β-sandwich domain, a catalytic core, and, finally, β-barrels 1 and 2. FXIII is activated following cleavage of its A-subunits by thrombin. The resultant transglutaminase activity leads to increased resistance of fibrin clots to fibrinolysis. Objectives To assess the functional roles of β-barrels 1 and 2 in FXIII, we expressed and characterized the full-length FXIII A-subunit (FXIII-A) and variants truncated to residue 628 (truncated to β-barrel 1 [TB1]), residue 515 (truncated to catalytic core [TCC]), and residue 184 (truncated to β-sandwich). Methods Proteins were analyzed by gel electrophoresis, circular dichroism, fluorometric assays, and colorimetric activity assays, clot structure was analyzed by turbidity measurements and confocal microscopy, and clot formation was analyzed with a Chandler loop system. Results and Conclusions Circular dichroism spectroscopy and tryptophan fluorometry indicated that full-length FXIII-A and the truncation variants TCC and TB1 retain their secondary and tertiary structure. Removal of β-barrel 2 (TB1) resulted in total loss of transglutaminase activity, whereas the additional removal of β-barrel 1 (TCC) restored enzymatic activity to ~ 30% of that of full-length FXIII-A. These activity trends were observed with physiological substrates and smaller model substrates. Our data suggest that the β-barrel 1 domain protects the active site cysteine in the FXIII protransglutaminase, whereas the β-barrel 2 domain is necessary for exposure of the active site cysteine during activation. This study demonstrates the importance of individual β-barrel domains in modulating access to the FXIII active site region.
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Affiliation(s)
- E. L. Hethershaw
- Discovery and Translational Science DepartmentLeeds Institute for Cardiovascular and Metabolic MedicineFaculty of Medicine and HealthUniversity of LeedsLeedsUK
| | - P. J. Adamson
- Discovery and Translational Science DepartmentLeeds Institute for Cardiovascular and Metabolic MedicineFaculty of Medicine and HealthUniversity of LeedsLeedsUK
| | - K. A. Smith
- Discovery and Translational Science DepartmentLeeds Institute for Cardiovascular and Metabolic MedicineFaculty of Medicine and HealthUniversity of LeedsLeedsUK
| | | | - R. J. Pease
- Discovery and Translational Science DepartmentLeeds Institute for Cardiovascular and Metabolic MedicineFaculty of Medicine and HealthUniversity of LeedsLeedsUK
| | - S. E. Radford
- Astbury Centre for Structural Molecular BiologySchool of Molecular and Cellular BiologyUniversity of LeedsLeedsUK
| | - P. J. Grant
- Discovery and Translational Science DepartmentLeeds Institute for Cardiovascular and Metabolic MedicineFaculty of Medicine and HealthUniversity of LeedsLeedsUK
| | - R. A. S. Ariëns
- Discovery and Translational Science DepartmentLeeds Institute for Cardiovascular and Metabolic MedicineFaculty of Medicine and HealthUniversity of LeedsLeedsUK
| | - M. C. Maurer
- Chemistry DepartmentUniversity of LouisvilleLouisvilleKYUSA
| | - H. Philippou
- Discovery and Translational Science DepartmentLeeds Institute for Cardiovascular and Metabolic MedicineFaculty of Medicine and HealthUniversity of LeedsLeedsUK
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Hengsawas Surasarang S, Florova G, Komissarov AA, Shetty S, Idell S, Williams RO. Formulation for a novel inhaled peptide therapeutic for idiopathic pulmonary fibrosis. Drug Dev Ind Pharm 2017; 44:184-198. [PMID: 28835128 DOI: 10.1080/03639045.2017.1371736] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
A caveolin-1 scaffolding domain, CSP7, is a newly developed peptide for the treatment of idiopathic pulmonary fibrosis. To develop a CSP7 formulation for further use we have obtained, characterized and compared a number of lyophilized formulations of CSP7 trifluoroacetate with DPBS and in combination with excipients (mannitol and lactose at molar ratios 1:5, 70 and 140). CSP7 trifluoroacetate was stable (>95%) in solution at 5 and 25 °C for up to 48 h and tolerated at least 5 freeze/thaw cycles. Lyophilized cakes of CSP7 trifluoroacetate with excipients were stable (>96%) for up to 4 weeks at room temperature (RT), and retained more than 98% of the CSP7 trifluoroacetate in the solution at 8 h after reconstitution at RT. The lyophilized CSP7 formulations were stable for up to 10 months at 5 °C protected from moisture. Exposure of the lyophilized cakes of CSP7 to 75% relative humidity (RH) resulted in an increase in the absorbed moisture, promoted crystallization of the excipients and induced reversible formation of CSP7 aggregates. Increased molar ratio of mannitol slightly affected formation of the aggregates. In contrast, lactose significantly decreased (up to 20 times) aggregate formation with apparent saturation at the molar ratio of 1:70. The possible mechanisms of stabilization of CSP7 trifluoroacetate in solid state by lactose include physical state of the bulking agent and the interactions between lactose and CSP7 trifluoroacetate (e.g. formation of a Schiff base with the N-terminal amino group of CSP7). Finally, CSP7 trifluoroacetate exhibited excellent stability during nebulization of formulations containing mannitol or lactose.
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Affiliation(s)
| | - Galina Florova
- b School of Medical Biological Sciences , The University of Texas Health Science Center at Tyler , Tyler , TX , USA
| | - Andrey A Komissarov
- b School of Medical Biological Sciences , The University of Texas Health Science Center at Tyler , Tyler , TX , USA
| | - Sreerama Shetty
- b School of Medical Biological Sciences , The University of Texas Health Science Center at Tyler , Tyler , TX , USA
| | - Steven Idell
- b School of Medical Biological Sciences , The University of Texas Health Science Center at Tyler , Tyler , TX , USA
| | - Robert O Williams
- a Division of Pharmaceutics , College of Pharmacy, The University of Texas at Austin , Austin , TX , USA
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Ponce R, Armstrong K, Andrews K, Hensler J, Waggie K, Heffernan J, Reynolds T, Rogge M. Safety of Recombinant Human Factor XIII in a Cynomolgus Monkey Model of Extracorporeal Blood Circulation. Toxicol Pathol 2017; 33:702-10. [PMID: 16243775 DOI: 10.1080/15459620500330625] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Factor XIII (FXIII) is a thrombin-activated plasma coagulation factor critical for blood clot stabilization and longevity. Administration of exogenous FXIII to replenish depleted stores after major surgery, including cardiopulmonary bypass, may reduce bleeding complications and transfusion requirements. Thus, a model of extracorporeal circulation (ECC) was developed in adult male cynomolgus monkeys ( Macaca fascicularis) to evaluate the nonclinical safety of recombinant human FXIII (rFXIII). The hematological and coagulation profile in study animals during and after 2 h of ECC was similar to that reported for humans during and after cardiopulmonary bypass, including observations of anemia, thrombocytopenia, and activation of coagulation and platelets. Intravenous slow bolus injection of 300 U/kg (2.1 mg/kg) or 1000 U/kg (7 mg/kg) rFXIII after 2 h of ECC was well tolerated in study animals, and was associated with a dose-dependent increase in FXIII activity. No clinically significant effects in respiration, ECG, heart rate, blood pressure, body temperature, clinical chemistry, hematology (including platelet counts), or indicators of thrombosis (thrombin:antithrombin complex and D-Dimer) or platelet activation (platelet factor 4 and beta-thromboglobulin) were related to rFXIII administration. Specific examination of brain, heart, lung, liver, and kidney from rFXIII-treated animals provided no evidence of histopathological alterations suggestive of subclinical hemorrhage or thrombosis. Taken as a whole, the results demonstrate the ECC model suitably replicated the clinical presentation reported for humans during and after cardiopulmonary bypass surgery, and do not suggest significant concerns regarding use of rFXIII in replacement therapy after extracorporeal circulation.
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Affiliation(s)
- R Ponce
- ZymoGenetics, Inc, Seattle, Washington 98102, USA.
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Handrkova H, Schroeder V, Kohler HP. The activation peptide of coagulation factor XIII is vital for its expression and stability. J Thromb Haemost 2015; 13:1449-58. [PMID: 26083359 DOI: 10.1111/jth.13035] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2014] [Accepted: 05/31/2015] [Indexed: 01/31/2023]
Abstract
BACKGROUND The human activation peptide of factor XIII (AP-FXIII) comprises the first 37 amino acids of the N-terminus and holds the FXIII in an inactive state. FXIII is activated either proteolytically by cleavage of AP-FXIII by thrombin, or non-proteolytically by high calcium concentrations. OBJECTIVE To investigate the role of AP-FXIII in the expression and stability of FXIII. METHODS We cloned 13 FXIII variants with progressive truncations of AP-FXIII from the N-terminus (delN-FXIII-A), expressed them in mammalian cells, and measured their thermostability, activation, and transglutaminase activity. We also used in silico calculations to analyze the stability of hypothetical delN-FXIII dimers and to identify crucial motifs within AP-FXIII. RESULTS Variants with deletions longer than the first 10 amino acids and an R11Q point mutant were not expressed as proteins. In silico calculations indicated that the sequence (8) FGGR(12) R plays a substantial role in intersubunit interactions in FXIII-A2 homodimers. In agreement with this prediction, the temperature stability of delN-FXIII variants decreased with increasing length of deletion. These results may suggest a role of the N-terminus of AP-FXIII in dimer stability. Substantial sequence homology was found among activation peptides of vertebrate and even invertebrate (crustacean) FXIII-A orthologs, which further supports our conclusion. CONCLUSIONS We conclude that deletion of 11 or more N-terminal amino acids disrupts intersubunit interactions, which may prevent FXIII-A2 homodimer formation. Therefore, AP-FXIII plays an important role in the stability of the FXIII-A2 dimer.
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Affiliation(s)
- H Handrkova
- Hemostasis Research Laboratory, University Clinic of Hematology, University Hospital of Bern, Bern, Switzerland
- Department of Clinical Research, University of Bern, Bern, Switzerland
| | - V Schroeder
- Hemostasis Research Laboratory, University Clinic of Hematology, University Hospital of Bern, Bern, Switzerland
- Department of Clinical Research, University of Bern, Bern, Switzerland
| | - H P Kohler
- Hemostasis Research Laboratory, University Clinic of Hematology, University Hospital of Bern, Bern, Switzerland
- Department of Clinical Research, University of Bern, Bern, Switzerland
- Department of Medicine, Spital Netz Bern Hospitals Tiefenau Ziegler, Bern, Switzerland
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Muszbek L, Bereczky Z, Bagoly Z, Komáromi I, Katona É. Factor XIII: a coagulation factor with multiple plasmatic and cellular functions. Physiol Rev 2011; 91:931-72. [PMID: 21742792 DOI: 10.1152/physrev.00016.2010] [Citation(s) in RCA: 332] [Impact Index Per Article: 25.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Factor XIII (FXIII) is unique among clotting factors for a number of reasons: 1) it is a protransglutaminase, which becomes activated in the last stage of coagulation; 2) it works on an insoluble substrate; 3) its potentially active subunit is also present in the cytoplasm of platelets, monocytes, monocyte-derived macrophages, dendritic cells, chondrocytes, osteoblasts, and osteocytes; and 4) in addition to its contribution to hemostasis, it has multiple extra- and intracellular functions. This review gives a general overview on the structure and activation of FXIII as well as on the biochemical function and downregulation of activated FXIII with emphasis on new developments in the last decade. New aspects of the traditional functions of FXIII, stabilization of fibrin clot, and protection of fibrin against fibrinolysis are summarized. The role of FXIII in maintaining pregnancy, its contribution to the wound healing process, and its proangiogenic function are reviewed in details. Special attention is given to new, less explored, but promising fields of FXIII research that include inhibition of vascular permeability, cardioprotection, and its role in cartilage and bone development. FXIII is also considered as an intracellular enzyme; a separate section is devoted to its intracellular activation, intracellular action, and involvement in platelet, monocyte/macrophage, and dendritic cell functions.
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Affiliation(s)
- László Muszbek
- Clinical Research Center and Thrombosis, Haemostasis and Vascular Biology Research Group of the Hungarian Academy of Sciences, University of Debrecen, Medical and Health Science Center, Debrecen, Hungary.
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Wang W. Protein aggregation and its inhibition in biopharmaceutics. Int J Pharm 2005; 289:1-30. [PMID: 15652195 DOI: 10.1016/j.ijpharm.2004.11.014] [Citation(s) in RCA: 687] [Impact Index Per Article: 36.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2004] [Revised: 08/20/2004] [Accepted: 11/12/2004] [Indexed: 12/21/2022]
Abstract
Protein aggregation is arguably the most common and troubling manifestation of protein instability, encountered in almost all stages of protein drug development. Protein aggregation, along with other physical and/or chemical instabilities of proteins, remains to be one of the major road barriers hindering rapid commercialization of potential protein drug candidates. Although a variety of methods have been used/designed to prevent/inhibit protein aggregation, the end results are often unsatisfactory for many proteins. The limited success is partly due to our lack of a clear understanding of the protein aggregation process. This article intends to discuss protein aggregation and its related mechanisms, methods characterizing protein aggregation, factors affecting protein aggregation, and possible venues in aggregation prevention/inhibition in various stages of protein drug development.
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Affiliation(s)
- Wei Wang
- Biotechnology Division, Bayer HealthCare, 800 Dwight Way, Berkeley, CA 94701, USA.
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Affiliation(s)
- R Anwar
- Molecular Medicine Unit, University of Leeds, St. James University, UK
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Abstract
One of the most challenging tasks in the development of protein pharmaceuticals is to deal with physical and chemical instabilities of proteins. Protein instability is one of the major reasons why protein pharmaceuticals are administered traditionally through injection rather than taken orally like most small chemical drugs. Protein pharmaceuticals usually have to be stored under cold conditions or freeze-dried to achieve an acceptable shelf life. To understand and maximize the stability of protein pharmaceuticals or any other usable proteins such as catalytic enzymes, many studies have been conducted, especially in the past two decades. These studies have covered many areas such as protein folding and unfolding/denaturation, mechanisms of chemical and physical instabilities of proteins, and various means of stabilizing proteins in aqueous or solid state and under various processing conditions such as freeze-thawing and drying. This article reviews these investigations and achievements in recent years and discusses the basic behavior of proteins, their instabilities, and stabilization in aqueous state in relation to the development of liquid protein pharmaceuticals.
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Affiliation(s)
- W Wang
- Biotechnology, Bayer Corporation, 800 Dwight Way, Berkeley, CA 94701, USA.
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Affiliation(s)
- L Muszbek
- Department of Clinical Biochemistry and Molecular Pathology, University Medical School of Debrecen, Hungary.
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Kreilgaard L, Jones LS, Randolph TW, Frokjaer S, Flink JM, Manning MC, Carpenter JF. Effect of Tween 20 on freeze-thawing- and agitation-induced aggregation of recombinant human factor XIII. J Pharm Sci 1998; 87:1597-603. [PMID: 10189273 DOI: 10.1021/js980126i] [Citation(s) in RCA: 186] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Agitation- and freeze-thawing-induced aggregation of recombinant human factor XIII (rFXIII) is due to interfacial adsorption and denaturation at the air-liquid and ice-liquid interfaces. The aggregation pathway proceeds through soluble aggregates to formation of insoluble aggregates regardless of the denaturing stimuli. A nonionic surfactant, polyoxyethylene sorbitan monolaurate (Tween 20), greatly reduces the rate of formation of insoluble aggregates as a function of surfactant concentration, thereby stabilizing native rFXIII. Maximum protection occurs at concentrations close to the critical micelle concentration (cmc), independent of initial protein concentration. To study the mechanistic aspects of the surfactant-induced stabilization, a series of spectroscopic studies were conducted. Electron paramagnetic resonance spectroscopy indicates that binding is not occurring between Tween 20 and either the native state or a folding intermediate state of rFXIII. Further, circular dichroism spectroscopy suggests that Tween 20 does not prevent the secondary structural changes induced upon guanidinium hydrochloride-induced unfolding. Taken together, these results imply that Tween 20 protects rFXIII against freeze-thawing- and agitation-induced aggregation primarily by competing with stress-induced soluble aggregates for interfaces, inhibiting subsequent transition to insoluble aggregates.
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Affiliation(s)
- L Kreilgaard
- The Department of Pharmaceutics, Royal Danish School of Pharmacy, Copenhagen
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Molecular Mechanisms of Type II Factor XIII Deficiency: Novel Gly562-Arg Mutation and C-Terminal Truncation of the A Subunit Cause Factor XIII Deficiency as Characterized in a Mammalian Expression System. Blood 1998. [DOI: 10.1182/blood.v91.8.2830.2830_2830_2838] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To explore the biological and clinical implications of the structure/function relationships in factor XIII, mutations in two patients with type II deficiency were identified and characterized in a mammalian expression system. Nucleotide sequence analysis of the A subunit gene showed that case no. 1 had a deletion of 4 bp (AATT) in exon XI and that, in case no. 2, Gly562 (GGG) had been replaced by Arg(AGG). The deletion in case no. 1 leads to a premature termination at codon 464. Restriction digestion of amplified DNAs confirmed that both cases were homozygous for their respective mutations. Reverse transcription-polymerase chain reaction analysis demonstrated that the level of mRNA was greatly reduced in case no. 1, whereas the level of mutant mRNA expressed in case no. 2 was normal. Molecular modeling calculated that Arg562 changed the conformation of the A subunit, suggesting misfolding and/or destabilization of the molecule. To determine how these mutations impaired synthesis of the A subunit, recombinant A subunits bearing the mutations were expressed in mammalian cells. Pulse-chase experiments showed that the mutants were synthesized normally but disappeared rapidly, whereas the wild-type remained. These results indicate that both mutant proteins with an altered conformation become prone to rapid degradation, resulting in factor XIII deficiency in these patients.
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Matsuka YV, Migliorini MM, Ingham KC. Cross-linking of fibronectin to C-terminal fragments of the fibrinogen alpha-chain by factor XIIIa. JOURNAL OF PROTEIN CHEMISTRY 1997; 16:739-45. [PMID: 9365922 DOI: 10.1023/a:1026307731751] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Fibronectin binds specifically to fibrin and is covalently cross-linked to the fibrin alpha chain by activated factor XIII (XIIIa). This reaction is important for wound healing. Here we investigate XIIIa-catalyzed cross-linking of fibronectin and some of its fragments to a recombinant fragment representing the COOH-terminal 30 kDa of the fibrin alpha chain (alpha C30K:His 368-Val 610). Only fibronectin and those fragments containing an intact NH2-terminus were able to form cross-linked complexes. As many as 10 of the 17 lysines in alpha C30K can serve as amine donors in this reaction. Analysis of the rate of XIIIa-catalyzed cross-linking of fibronectin NH2-terminal peptides and fragments with alpha C30K revealed that the presence of the first type I "finger" module accelerates the cross-linking reaction; addition of fingers 2-5 had no further effect.
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Affiliation(s)
- Y V Matsuka
- Holland Laboratory, American Red Cross, Rockville, Maryland 20855, USA
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Conejero-Lara F, Parrado J, Azuaga AI, Smith RA, Ponting CP, Dobson CM. Thermal stability of the three domains of streptokinase studied by circular dichroism and nuclear magnetic resonance. Protein Sci 1996; 5:2583-91. [PMID: 8976567 PMCID: PMC2143313 DOI: 10.1002/pro.5560051221] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Streptococcus equisimilis streptokinase (SK) is a single-chain protein of 414 residues that is used extensively in the clinical treatment of acute myocardial infarction due to its ability to activate human plasminogen (Plg). The mechanism by which this occurs is poorly understood due to the lack of structural details concerning both molecules and their complex. We reported recently (Parrado J et al., 1996, Protein Sci 5:693-704) that SK is composed of three structural domains (A, B, and C) with a C-terminal tail that is relatively unstructured. Here, we report thermal unfolding experiments, monitored by CD and NMR, using samples of intact SK, five isolated SK fragments, and two two-chain noncovalent complexes between complementary fragments of the protein. These experiments have allowed the unfolding processes of specific domains of the protein to be monitored and their relative stabilities and interdomain interactions to be characterized. Results demonstrate that SK can exist in a number of partially unfolded states, in which individual domains of the protein behave as single cooperative units. Domain B unfolds cooperatively in the first thermal transition at approximately 46 degrees C and its stability is largely independent of the presence of the other domains. The high-temperature transition in intact SK (at approximately 63 degrees C) corresponds to the unfolding of both domains A and C. Thermal stability of domain C is significantly increased by its isolation from the rest of the chain. By contrast, cleavage of the Phe 63-Ala 64 peptide bond within domain A causes thermal destabilization of this domain. The two resulting domain portions (A1 and A2) adopt unstructured conformations when separated. A1 binds with high affinity to all fragments that contain the A2 portion, with a concomitant restoration of the native-like fold of domain A. This result demonstrates that the mechanism whereby A1 stimulates the plasminogen activator activities of complementary SK fragments is the reconstitution of the native-like structure of domain A.
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Affiliation(s)
- F Conejero-Lara
- Oxford Centre for Molecular Sciences, University of Oxford, United Kingdom
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Abstract
The availability of sensitive calorimetric instrumentation has led to a considerable increase in thermodynamic studies of proteins, nucleic acids, and their interactions. This article reviews some of the recent contributions of calorimetry to characterizing the thermodynamic origins of protein and nucleic acid stability and conformational preferences, as well as the interactions of proteins with each other, with small molecules, and with nucleic acids.
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Affiliation(s)
- G E Plum
- Department of Chemistry, Rutgers, State University of New Jersey, Piscataway 08855, USA
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