Binding of factor VIII to membranes containing phosphatidyl-L-serine (Ptd-L-Ser) is mediated, in part, by a motif localized to the C2 domain. We evaluated a putative membrane-binding role of the C1 domain using an anti-C1 antibody fragment, KM33 scFv , and factor VIII mutants with an altered KM33 epitope. We prepared a dual mutant Lys2092/Phe2093 3 Ala/ Ala (fVIII YFP 2092/93) and 2 single mutants Lys2092 3 Ala and Phe2093 3 Ala. KM33 scFv inhibited binding of fluorescein-labeled factor VIII to synthetic membranes and inhibited at least 95% of factor Xase activity. fVIII YFP 2092/93 had 3-fold lower affinity for membranes containing 15% Ptd-L-Ser but more than 10-fold reduction in affinity for membranes with 4% Ptd-L-Ser. In a microtiter plate, KM33 scFv was additive with an anti-C2 antibody for blocking binding to vesicles of 15% Ptd-L-Ser, whereas either antibody blocked binding to vesicles of 4% Ptd-L-Ser. KM33 scFv inhibited binding to platelets and fVIII YFP 2092/93 had reduced binding to A23187-stimulated platelets. fVIII YFP 2092 exhibited normal activity at various Ptd-L-Ser concentrations, whereas fVIII YFP 2093 showed a reduction of activity with Ptd-L-Ser less than 12%. fVIII YFP 2092/93 had a greater reduction of activity than either single mutant. These results indicate that Lys 2092 and Phe 2093 are elements of a membrane-binding motif on the factor VIII C1 domain. (Blood. 2009;114:3938-3946) Introduction Factor VIII functions as a cofactor in the membrane-bound intrinsic factor Xase complex. Together with the enzyme factor IXa, activated factor VIII binds to phosphatidyl-L-serine (Ptd-L-Ser)-containing membranes 1,2 to form an enzyme complex that cleaves the zymogen factor X to factor Xa. 3,4 Factor Xa is thereafter responsible for catalyzing prothrombin cleavage to thrombin. 5 The importance of the factor Xase complex is illustrated by the disease hemophilia, in which a deficiency of factor VIII (hemophilia A) or factor IX (hemophilia B) leads to life-threatening bleeding. Despite the central importance of membrane binding, this aspect of factor VIII function remains poorly understood. Factor VIII is synthesized as a single polypeptide chain containing 2351 amino acids (molecular weight, 280 kDa) and shows a domain structure of A1-a1-A2-a2-B-a3-A3-C1-C2, where a1, a2, and a3 are spacer regions that separate the domains from each other. 6 Factor VIII is homologous to factor V in amino acid sequence and domain structure. 7 The A domains are homologous with ceruloplasmin, the C domains with discoidin I, and with lactadherin, 8,9 and the B domain is unique to each protein. 10 The A domains mediate the dominant interactions with factor IXa and factor X in the factor Xase complex, whereas binding to Ptd-L-Ser-containing membranes is mediated predominantly by the C2 domain. 11-15 The structure-function relationships of factor V resemble those of factor VIII in that the A domains mediate the dominant interactions with the enzyme and substrate and the C2 domain mediates the dominant membrane-binding inter...

Vinyl chloride reacts with cellular DNA producing 3,N4-etheno-2'-deoxycytidine (epsilonC) along with other exocyclic adducts. The solution structure of an oligodeoxynucleotide duplex containing an epsilonC.dG base pair was determined by high-resolution NMR spectroscopy and molecular dynamics simulations. NMR data indicated that the duplex adopts a right-handed helical structure having all residues in anti orientation around the glycosylic torsion angle. The epsilonC adduct has a sugar pucker in the C3'-endo/C4'-exo region while the rest of the residues are in the C2'-endo/C3'-exo range. NOE interactions established Watson-Crick alignments for canonical base pairs of the duplex. The imino proton of the lesion-containing base pair resonated as a sharp signal that was resistant to water exchange, suggesting hydrogen bonding. Restrained molecular dynamics simulations generated three-dimensional models in excellent agreement with the spectroscopic data. The refined structures are slightly bent at the lesion site without major perturbations of the sugar-phosphate backbone. The adduct is displaced and shifted toward the major groove of the helix while its partner on the complementary strand remains stacked. The epsilonC(anti).dG(anti) base pair alignment is sheared and stabilized by the formation of hydrogen bonds. The biological implications of structures of epsilonC-containing DNA duplexes are discussed.

The d(C-G-T-A-C-epsilon C-C-A-T-G-C).d(G-C-A-T-G-A-G-T-A-C-G) oligodeoxynucleotide duplex containing the 3, N4-etheno-2'-deoxycytidine adduct positioned opposite 2'-deoxyadenosine in the center of the helix has been analyzed by proton NMR spectroscopy and restrained molecular dynamics. The spectroscopic data establish a right-handed duplex, with sugar puckers in the C2'-endo/C3'-exo range, residues adopting an anti conformation around the glycosidic torsion angle and, with the exception of epsilon C.dA, Watson-Crick hydrogen bond alignment for all base pairs. Molecular dynamics simulations, restrained by the full relaxation matrix approach, produced a three-dimensional model with an NMR R-factor of 7%. The duplex structure shows no significant perturbation of the sugar-phosphate backbone, which remains in B-form. The exocyclic adduct and its partner dA are incorporated into the helix without producing a noticeable kink. The epsilon C.dA alignment adopts a staggered conformation with each residue displaced toward the 5'-terminus and intercalated between bases on the opposite strand, without increase of inter-phosphate distances. The partial intercalation of the epsilon C (anti).dA(anti) alignment allows stacking between the aromatic rings of epsilon C and dA and with base pairs adjacent to the lesion, suggesting an important role played by hydrophobic forces in the stabilization of the solution structure.

Factor VIII functions as a cofactor for Factor IXa in a membrane-bound enzyme complex. Membrane binding accelerates the activity of the Factor VIIIa–Factor IXa complex approx. 100000-fold, and the major phospholipid-binding motif of Factor VIII is thought to be on the C2 domain. In the present study, we prepared an fVIII-C2 (Factor VIII C2 domain) construct from Escherichia coli, and confirmed its structural integrity through binding of three distinct monoclonal antibodies. Solution-phase assays, performed with flow cytometry and FRET (fluorescence resonance energy transfer), revealed that fVIII-C2 membrane affinity was approx. 40-fold lower than intact Factor VIII. In contrast with the similarly structured C2 domain of lactadherin, fVIII-C2 membrane binding was inhibited by physiological NaCl. fVIII-C2 binding was also not specific for phosphatidylserine over other negatively charged phospholipids, whereas a Factor VIII construct lacking the C2 domain retained phosphatidyl-L-serine specificity. fVIII-C2 slightly enhanced the cleavage of Factor X by Factor IXa, but did not compete with Factor VIII for membrane-binding sites or inhibit the Factor Xase complex. Our results indicate that the C2 domain in isolation does not recapitulate the characteristic membrane binding of Factor VIII, emphasizing that its role is cooperative with other domains of the intact Factor VIII molecule.

The exocyclic 3,N4-etheno-2'-deoxycytidine adduct was incorporated at the center of the oligodeoxynucleotide duplex d(C-G-T-A-C-epsilon C-C-A-T-G-C).d (G-C-A-T-G-T-G-T-A-C-G), and its solution structure was analyzed using high-resolution proton NMR spectroscopy and molecular dynamics simulations. The experimental data indicate that the oligodeoxynucleotide duplex adopts a right-handed helical structure with sugar puckers in the C2'-endo/C3'-exo range and Watson-Crick hydrogen bond alignments for all base pairs. NOE connectivities established a syn orientation for the glycosidic torsion angle of the exocyclic adduct. Restrained molecular dynamics simulations, using the full relaxation matrix approach, produced a three-dimensional model in agreement with the experimental data. The structure shows only minor perturbations in the sugar-phosphate backbone and a 27 degrees bend of the helical axis at the lesion site. On the refined model a well-formed hydrogen bond between T (N3H) and epsilon C(N4) stabilizes the epsilon C(syn).T(anti) base pair alignment, reflecting the preference of the adduct for the syn orientation. Furthermore, the epsilon C(syn).T(anti) base pair stacks with flanking base pairs. We discuss a correlation between the mutagenic properties of the adduct and the three-dimensional structure of the epsilon C.dA and epsilon C.T duplexes.

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Hydrogen cyanide, cyanogen chloride and phosgene are produced in tremendously large quantities today by the chemical industry. The compounds are also particularly attractive to foreign states and terrorists seeking an inexpensive mass-destruction capability. Along with contemporary warfare agents, therefore, the US Army evaluates protective equipment used by warfighters and domestic emergency responders against the compounds, and requires their certification at > or = 95 carbon atom % before use. We have investigated the (13)C spin-lattice relaxation behavior of the compounds to develop a quantitative NMR method for characterizing chemical lots supplied to the Army. Behavior was assessed at 75 and 126 MHz for temperatures between 5 and 15 degrees C to hold the compounds in their liquid states, dramatically improving detection sensitivity. T(1) values for cyanogen chloride and phosgene were somewhat comparable, ranging between 20 and 31 s. Hydrogen cyanide values were significantly shorter at 10-18 s, most likely because of a (1)H--(13)C dipolar contribution to relaxation not possible for the other compounds. The T(1) measurements were used to derive relaxation delays for collecting the quantitative (13)C data sets. At 126 MHz, only a single data acquisition with a cryogenic probehead gave a signal-to-noise ratio exceeding that necessary for certifying the compounds at > or = 95 carbon atom % and 99% confidence. Data acquired at 75 MHz with a conventional probehead, however, required > or = 5 acquisitions to reach this certifying signal-to-noise ratio for phosgene, and >/= 12 acquisitions were required for the other compounds under these same conditions. In terms of accuracy and execution time, the NMR method rivals typical chromatographic methods.

Two-dimensional 1H-13C HSQC (heteronuclear single quantum correlation) and fast-HMQC (heteronuclear multiple quantum correlation) pulse sequences were implemented using a sensitivity-enhanced, cryogenic probehead for detecting compounds relevant to the Chemical Weapons Convention present in complex mixtures. The resulting methods demonstrated exceptional sensitivity for detecting the analytes at trace level concentrations. 1H-13C correlations of target analytes at < or = 25 microg/mL were easily detected in a sample where the 1H solvent signal was approximately 58,000-fold more intense than the analyte 1H signals. The problem of overlapping signals typically observed in conventional 1H spectroscopy was essentially eliminated, while 1H and 13C chemical shift information could be derived quickly and simultaneously from the resulting spectra. The fast-HMQC pulse sequences generated magnitude mode spectra suitable for detailed analysis in approximately 4.5 h and can be used in experiments to efficiently screen a large number of samples. The HSQC pulse sequences, on the other hand, required roughly twice the data acquisition time to produce suitable spectra. These spectra, however, were phase-sensitive, contained considerably more resolution in both dimensions, and proved to be superior for detecting analyte 1H-13C correlations. Furthermore, a HSQC spectrum collected with a multiplicity-edited pulse sequence provided additional structural information valuable for identifying target analytes. The HSQC pulse sequences are ideal for collecting high-quality data sets with overnight acquisitions and logically follow the use of fast-HMQC pulse sequences to rapidly screen samples for potential target analytes. Use of the pulse sequences considerably improves the performance of NMR spectroscopy as a complimentary technique for the screening, identification, and validation of chemical warfare agents and other small-molecule analytes present in complex mixtures and environmental samples.