A proton nuclear magnetic resonance investigation of histidyl residues in sickle hemoglobin

Using high-resolution proton nuclear magnetic resonance spectroscopy at 250 MHz, we have determined the individual pK values of 22 surface histidyl residues (11 per alpha beta dimer) of sickle hemoglobin in both deoxy and carbon monoxy forms. Seven histidyl residues in the deoxy form and three in the carbon monoxy form are found to have pK values and chemical shifts different from the corresponding ones in human normal adult hemoglobin. Two of these histidyl residues are the beta 2 histidine and the beta 146 histidine, indicating that the conformations of the amino- and carboxyl-terminal regions of the beta chain in sickle hemoglobin are altered compared to those in human normal adult hemoglobin. The differences in the pK values of the additional surface histidyl residues between sickle and normal hemoglobins suggest that the effect of the amino acid substitution at the sixth position of the beta chain in sickle hemoglobin, namely, glutamic acid replaced by valine, is not restricted to the region around the mutation site but can extend to other regions in the protein molecule. In the deoxy form, the histidyl residues of sickle hemoglobin that have altered pK values and chemical shifts compared to the corresponding ones in human normal adult hemoglobin have been found to be sensitive to the early stages of the polymerization process [Russu, I.M., & Ho, C. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 6577-6581].

A proton nuclear magnetic resonance investigation of histidyl residues in human normal adult hemoglobin

High-resolution proton nuclear magnetic resonance (NMR) spectroscopy at 250 MHz has been used to titrate 22 individual surface histidyl residues (11 per alpha beta dimer) of human normal adult hemoglobin in both the deoxy and the carbon monoxy forms. The proton resonances of beta 2, beta 143, and beta 146 histidyl residues are assigned by a parallel 1H NMR titration of appropriate mutant and chemically modified hemoglobins. The pK values of the 22 histidyl residues investigated are found to range from 6.35 to 8.07 in the deoxy form and from 6.20 to 7.87 in the carbon monoxy form, in the presence of 0.1 M Bis-Tris or 0.1 M Tris buffer in D2O with chloride ion concentrations varying from 5 to 60 mM at 27 degrees C. Four histidyl residues in the deoxy form and one histidyl residue in the carbon monoxy form are found to have proton nuclear magnetic resonance titration curves that deviate greatly from that predicted by the simple proton dissociation equilibrium of a single ionizable group. The proton nuclear magnetic resonance data are used to ascertain the role of several surface histidyl residues in the Bohr effect of hemoglobin under the above-mentioned experimental conditions. Under these experimental conditions, we have found that (i) the beta 146 histidyl residues do not change their electrostatic environments significantly upon binding of ligand to deoxyhemoglobin and, thus, their contribution to the Bohr effect is negligible, (ii) the beta 2 histidyl residues have a negative contribution to the Bohr effect, and (iii) the total contribution of the 22 histidyl residues investigated here to the Bohr effect is, in magnitude, comparable to the Bohr effect observed experimentally. These results suggest that the molecular mechanism of the Bohr effect proposed by Perutz [Perutz, M.F. (1970) Nature (London) 228, 726-739] is not unique and that the detailed mechanism depends on experimental conditions, such as the solvent composition.

Proton longitudinal relaxation investigation of histidyl residues in human normal adult hemoglobin

The longitudinal relaxation of the C2 protons of surface histidyl residues as well as other aromatic protons of human normal adult deoxyhemoglobin investigated at 360 MHz is discussed in terms of the theory proposed by Kalk and Berendsen for the proton longitudinal relaxation in proteins (Kalk, A., and H.J.C. Berendsen. 1976. J. Magn. Reson. 24:343-366). The role of the four paramagnetic iron atoms of deoxyhemoglobin as fast-relaxing sinks for the overall proton longitudinal relaxation is evaluated according to the model proposed by Bloembergen for the relaxation of nuclei in crystals containing paramagnetic centers (Bloembergen, N. 1949. Physica. 15:386-426). The results suggest that the effectiveness of the paramagnetic iron atoms of deoxyhemoglobin for the overall proton longitudinal relaxation is reduced as a result of slower spin diffusion and wide distribution of methyl groups within the hemoglobin molecule. Thus, deoxyhemoglobin provides a good model for investigating the influence of cross relaxation on proton longitudinal relaxation in proteins at the slow motion limit and in the presence of paramagnetic centers. For the C2 protons of surface histidyl residues, we show that the cross relaxation resulting from the interresidue dipolar interaction makes an important contribution to their longitudinal relaxation.

A proton nuclear magnetic resonance investigation of proximal histidyl residues in human normal and abnormal hemoglobins. A probe for the heme pocket

Proton nuclear magnetic resonance spectroscopy at 250 MHz has been used to investigate the conformations of proximal histidyl residues of human normal adult hemoglobin, hemoglobin Kempsey [beta 99(G1) Asp leads to Asn], hemoglobin Osler [beta 145(HC2) Tyr leads to Asp], and hemoglobin McKees Rocks [beta 145(HC2) Tyr leads to Term] around neutral pH in H2O at 27 degrees C, all in the deoxy form. Two resonances that occur between 58 and 76 ppm downfield from the water proton signal have been assigned to the hyperfine shifted proximal histidyl NH-exchangeable protons of the alpha- and beta-chains of deoxyhemoglobin. These two resonances are sensitive to the quaternary state of hemoglobin, amino acid substitutions in the alpha 1 beta 2-subunit interface and in the carboxy-terminal region of the beta-chain, and the addition of organic phosphates. The experimental results show that there are differences in the heme pockets among these four hemoglobins studied. The structural and dynamic information derived from the hyperfine shifted proximal histidyl NH-exchangeable proton resonances complement that obtained from the ferrous hyperfine shifted and exchangeable proton resonances of deoxyhemoglobin over the spectral region from 5 to 20 ppm downfield from H2O. The relationship between these findings and Perutz's stereochemical mechanism for the cooperative oxygenation of hemoglobin is discussed.

Synthesis and in vitro antimicrobial activity of 5-substituted 2H-1,3,5-thiadiazine-2,4(3H)-diones

A series of 6-substituted 2H-1,3,5-thiadiazine-2,4(3H)-diones (1a-m) was prepared by treatment of alkyl, aryl, and heterocyclic primary thioamides with phenoxycarbonyl isocyanate to give N-(phenoxycarbonyl)-N'-thioacylureas, which gave 1 upon heating in refluxing xylene solution or upon treatment with aqueous sodium carbonate solution followed by acidification. 1H NMR and infrared spectral evidence indicates that the 6-alkyl derivatives 1a,b,l,m exist predominately in the exocyclic alkylidene tautomeric form. The major product obtained from alkaline and acid hydrolysis of the 6-phenyl derivative 1c was found to be benzoic acid and benzoylurea, respectively. The majority of compounds 1a-m exhibited in vitro antifungal activity against Candida albicans and Trichophyton mentagrophytes. Several derivatives, 1b-d,h,j, displayed minimum inhibitory concentration values below 2 micrograms/mL against Trichophyton mentagrophytes. Four derivatives, 1c,e,g,h, inhibited the growth of Seratia marcesens, Staphylococcus aureus, and Staphylococcus epidermis in an in vitro sensitivity disk assay. 2-Furyl derivative 1h displayed antileukemic activity against P-388 lymphocytic leukemia.

A biophysical study of protein-lipid interactions in membranes of Escherichia coli. Fluoromyristic acid as a probe

Fluorine-19 nuclear magentic resonance spectroscopy and transport assays have been used to investigate and compare the membrane properties of unsaturated fatty acid auxotrophs of two strains of Escherichia coli, K1060B5 and ML 308-225-UFA-8. A fluorinated analog of myristic acid, 8, 8-difluoromyristic acid, can be incorporated into the membrane phospholipids by substitution for oleate in the growth medium. Growth for one generation on 8, 8-difluoromyristate results in a 20% content of fluorinated fatty acid in the membranes, changes in the protein to lipid ratio, and altered transport of methyl beta-D-thiogalactopyranoside. The differences in membrane composition and transport behavior seen in oleate supplemented E. coli K1060B5 relative to ML 308-225-UFA-8 are enhanced by the incorporation of 8, 8-difluoromyristate. The phase transition behavior becomes distinctly different and some differences in lipid organization persist above the transition temperature. Concomitantly, the rate and extent of concentration of methyl beta-D-thiogalactopyranoside are reduced two-fold more in E. coli K1060B5 compared to ML 308-225-UFA-8. Such behavior suggests that these fluorinated fatty acid supplemented strains of E. coli are useful to study subtle differences in protein-lipid interactions and their effects on the function of membrane-bound enzymes.

Deuterium NMR of specifically deuterated fluorine spin probes

Deuterium nuclear magnetic resonance spectra (at 55.3 MHz) have been obtained of 19F-2H double-labeled phospholipids in pure lipid bilayers, and of 2H-labeled lipid in a 19F-labeled bilayer, as a function of concentration, to assess the perturbing influence of 19F sites in lipid hydrocarbon chains. Order parameters of 2H-labeled sites adjacent to C-8 myristic fluorine probes in pure lipid bilayers, and 19F spin label order parameters themselves, are about 30% lower than those deduced from the use of nonperturbing 2H probes. The effect is intramolecular rather than intermolecular and presumably represents increased gauche states due to the increased size of the 19F label. This effect is consistent with the view that difluoromethylene fatty acyl chains function in a manner approximating that of unsaturated fatty acyl chains. The differences disappear in the presence of cholesterol at very high order parameters (Smol approximately 0.8 to 0.9). These results represent the first attempt at elucidating the perturbing effects of a high sensitivity probe (19F) and indicate that caution must be used when using spectroscopic probes to deduce the absolute magnitude of hydrocarbon chain order parameters.

Proton longitudinal relaxation investigation of histidyl residues of normal human adult and sickle deoxyhemoglobin: evidence for the existence of pregelation aggregates in sickle deoxyhemoglobin solutions

Proton nuclear magnetic resonance longitudinal-relaxation-rate measurements have been used to investigate the molecular events that occur during the early stages of the polymerization process of sickle hemoglobin. The longitudinal relaxation rates (T1-1) of the C2 protons of 11 observable surface histidyl residues in normal human adult and sickle hemoglobin in the deoxy state were measured in 0.1 M bis[(2-hydroxyethyl)imino]tris(hydroxymethyl)methane (pH 6.8) in 2H2O. These proton resonances in hemoglobin occur at a position 1.5-5.0 ppm downfield from that of residual water in 2H2O. The T1-1 values for the C2 protons of several surface histidyl residues in sickle hemoglobin in the deoxy state were sensitive to the temperature and the concentration of hemoglobin, factors known to have a profound effect on the polymerization process of sickle hemoglobin. For hemoglobin concentrations of 13.5% or less and temperatures of 25 degrees C or less, the T1-1 values in sickle hemoglobin solutions were the same as the corresponding values in normal hemoglobin, except for the C2 proton of beta 2 histidine, which had a larger T1-1 value. When the temperature or the hemoglobin concentration was increased (i) several additional histidine resonances in sickle hemoglobin solutions had larger T1-1 values than the corresponding ones in normal hemoglobin and (ii) the differences between the T1-1 values (sickle versus normal hemoglobin) of these histidine resonances as well as that of the beta 2 histidine resonance gradually increased. It is proposed that these results reflect the formation of small aggregates in the deoxygenated sickle hemoglobin solutions before gelation. In this model, the histidyl residues for which the T1-1 values are greatly increased in sickle hemoglobin solutions as compared with those in normal hemoglobin are viewed as being located in or near the "contact" areas between sickle hemoglobin molecules within the pregelation aggregates. Thus, this magnetic resonance technique can also be used to identify the intermolecular contacts in the polymerization of sickle hemoglobin.

Role of the beta 146 histidyl residue in the alkaline Bohr effect of hemoglobin

High-resolution proton nuclear magnetic resonance spectroscopy has been used to investigate the effects of inorganic anions, such as phosphate or chloride, on the alkaline Bohr effect of normal human adult hemoglobin. By monitoring the chemical shift of the C2 proton of the beta 146 histidyl residue as a function of pH, we have determined its pK values in both ligated and unligated forms. In the presence of 0.1 M Bis-Tris buffer (with chloride ion concentration ranging from 0.005 to 0.06 M) in D2O at 27 degrees C, the pK value of the beta 146 histidine of deoxyhemoglobin is 7.98 +/- 0.03 and that of (carbon monoxy)hemoglobin is 7.85 +/- 0.03. However, in the presence of 0.2 M phosphate and 0.2 M NaCl in D2O at 27 degrees C, the corresponding pK values are 8.08 and 7.14, as previously reported by this laboratory [Kilmartin, J. V., Breen, J. J., Roberts, G. C. K., & Ho, C. (1973) Proc. Natl. Acad. Sci. U.S.A. 70, 1246-1249]. This large difference in the pK value between the deoxy and carbon monoxy forms in the presence of 0.2 M phosphate and 0.2 M NaCl was interpreted as direct support for (1) the breaking of an intrasubunit salt bridge between beta 146 histidine and beta 94 aspartate when the hemoglobin molecule undergoes the quaternary structural transition as proposed by Perutz [Perutz, M. F. (1970) Nature (London) 228, 726-739] and (2) Perutz's suggestion that the beta 146 histidine is one of the amino acid residues responsible for the alkaline Bohr effect. The absence of a large change in the pK value of the beta 146 histidine in the presence of 0.1 M Bis-Tris buffer implies that (1) the above-mentioned intrasubunit salt bridge is not broken in going from the deoxy to the carbon monoxy form and (2) the beta 146 histidyl residue does not contribute significantly to the alkaline Bohr effect under these conditions. We have also found that in measuring the oxygen affinity of hemoglobin as a function of pH in the presence of 0.1 M Bis-Tris or 0.2 M phosphate plus 0.2 M NaCl (both in D2O), there is no significant difference in the alkaline Bohr effect in these two media. Hence, our results suggest that the detailed molecular mechanism for the Bohr effect depends on the experimental conditions.

A proton nuclear magnetic resonance investigation of histidine-binding protein J of Salmonella typhimurium: a model for transport of L-histidine across cytoplasmic membrane

Genetic evidence suggests that the high-affinity L-histidine transport in Salmonella typhimurium requires the participation of a periplasmic binding protein (histidine-binding protein J) and two other proteins (P and Q proteins). The histidine-binding protein J binds L-histidine as the first step in the high-affinity active transport of this amino acid across the cytoplasmic membrane. High-resolution proton nuclear magnetic resonance spectroscopy at 600 MHz is used to investigate the conformations of this protein in the absence and presence of substrate. Previous nuclear magnetic resonance results reported by this laboratory have shown that there are extensive spectral changes in this protein upon the addition of L-histidine. When resonances from individual amino acid residues of a protein can be resolved in the proton nuclear magnetic resonance spectrum, a great deal of detailed information about substrate-induced structural changes can be obtained. In order to gain a deeper insight into the nature of these structural changes, deuterated phenylalanine or tyrosine has been incorporated into the bacteria. Proton nuclear magnetic resonance spectra of selectively deuterated histidine-binding protein J were obtained and compared to the normal protein. Several of the proton resonances have been assigned to the various aromatic amino acid residues of this protein. A model for the high-affinity transport of L-histidine across the cytoplasmic membrane of S typhimurium is proposed. This model, which is a version of the pore model, assumes that both P and Q proteins are membrane-bound and that the interface between these two proteins forms the channel for the passage of substrate. The histidine-binding protein J serves as the "key" for the opening of the channel for the passage of L-histidine. In the absence of substrate, this channel or gate is closed owing to a lack of appropriate interactions among these three proteins. The channel can be opened upon receiving a specific signal from the "key"; namely, the substrate-induced conformational changes in the histidine-binding protein J molecule. This model is consistent with available experimental evidence for the high-affinity transport of L-histidine across the cytoplasmic membrane of S typhimurium.

Proton nuclear magnetic resonance and biochemical studies of oxygenation of human adult hemoglobin in deuterium oxide

The proton nuclear magnetic resonance spectrum of human adult deoxyhemoglobin in D2O in the region from 6 to 20 ppm downfield from the proton resonance of residual water shows a number of hyperfine shifted proton resonances that are due to groups on or near the alpha and beta hemes. The sensitivity of these resonances to the ligation of the heme groups and the assignment of these resonances to the alpha and beta chains provide an opportunity to investigate the cooperative oxygenation of an intact hemoglobin molecule in solution. By use of the nuclear magnetic resonance correlation spectroscopy technique, at least two resonances, one at approximately 18 ppm downfield from HDO due to the beta chain and the other at approximately 12 ppm due to the alpha chain, can be used to study the binding of oxygen to the alpha and beta chains of hemoglobin. The present results using approximately 12% hemoglobin concentration in 0.1 M Bistris buffer at pD 7 and 27 degrees C with and without organic phosphate show that there is no significant line broadening on oxygenation (from 0 to 50% saturation) to affect the determination of the intensities or areas of these resonances. It is found that the ratio of the intensity of the alpha-heme resonance at 12 ppm to that of the beta-heme resonance at 18 ppm is constant on oxygenation in the absence of organic phosphate but decreases in the presence of 2,3-diphosphoglycerate or inositol hexaphosphate, with the effect of the latter being the stronger. On oxygenation, the intensities of the alpha-heme resonance at 12 ppm and of the beta-heme resonance at 18 ppm decreases more than the total number of deoxy chains available as measured by the degree of O2 saturation of hemoglobin. This shows the sensitivity of these resonances to structural changes which are believed to occur in the unligated subunits upon the ligation of their neighbors in an intact tetrameric hemoglobin molecule. A comparison of the nuclear magnetic resonance data with the populations of the partially saturated hemoglobin tetramers (i.e., hemoglobin with one, two, or three oxygen molecules bound) leads to the conclusion that in the presence of organic phosphate the hemoglobin molecule with one oxygen bound maintains the beta-heme resonance at 18 ppm but not the alpha-heme resonance at 12 ppm. These resluts suggest that some cooperativity must exist in the deoxy quaternary structure of the hemoglobin molecule during the oxygenation process. Hence, these results are not consistent with the requirements of two-state concerted models for the oxygenation of hemoglobin. In addition, we have investigated the effect of D2O on the oxygenation of hemoglobin by measuring the oxygen dissociation curves of normal adult hemoglobin as a function of pH in D2O andH2O media. We have found that (1) the pH dependence of the oxygen equilibrium of hemoglobin (the Bohr effect) in higher pH in comparison to that in H2O medium and (2) the Hill coefficients are essentially the same in D2O and H2O media over the pH range from 6.0 to 8.2...

Proton nuclear magnetic resonance investigation of structural changes associated with cooperative oxygenation of human adult hemoglobin

The structural changes associated with cooperative oxygenation of human adult hemoglobin as a function of oxygen saturation in aqueous media at neutral pH and at 25-27 degrees C have been investigated by high-resolution proton nuclear magnetic resonance spectroscopy at 250 and 360 MHz. By monitoring the intensities of two hyperfine shifted proton resonances (at about -12 and -18 ppm from H(2)O) and two exchangeable proton resonances (at about -6.4 and -9.4 ppm from H(2)O) as a function of oxygenation, the amount of oxygen bound to the alpha and beta chains of a hemoglobin molecule can be determined and the relationship between tertiary and quaternary structural changes under a given set of experimental conditions can be investigated. These results suggest that: (i) in the absence of organic phosphates, there is no preferential O(2) binding to the alpha or beta chains; (ii) in the presence of organic phosphates, the alpha hemes have a higher affinity for O(2) as compared to the beta hemes; (iii) the ligand-induced structural changes in the hemoglobin molecule are not concerted; and (iv) some cooperativity must be present within the deoxy quaternary state during the oxygenation process. The variations of the exchangeable proton resonances as a function of oxygenation strongly suggest that the breaking of one or more inter- or intrasubunit linkages of a ligated subunit can affect similar linkages in unligated subunits within a tetrameric hemoglobin molecule. Thus, the present results show that two-state allosteric models are not adequate to describe the cooperative oxygenation of hemoglobin. In addition, the present results provide direct correlation to the ligand-induced structural changes (such as in the heme pockets and subunit interfaces) observed to occur in the crystals of deoxy- and oxy-like hemoglobin molecules and in the solution state.

A phosphorus-31 nuclear magnetic resonance investigation of intracellular environment in human normal and sickle cell blood

Intracellular pH and 2,3-diphosphoglycerate concentration in sickle cell amenia and normal human blood samples were measured by means of phosphorus-31 nuclear magnetic resonance spectroscopy. To monitor the concentrations of various internal phosphorylated metabolites of intact red blood cells, heparinized blood samples were used and were incubated at 37 degrees C with 5.6% C92, 25% O2, and 69.4% N2. The 31P chemical shifts of phosphorylated compounds, such as 2,3-diphosphoglycerate, adenosine 5'-triphosp-ate, and inorganic phosphate, depend on pH, and by using an appropriate calibration curve, the intracellular pH of intact erythrocytes can be obtained. The intracellular pH values in fresh sickl cell blood and normal blood were found to be 7.14 and 7.29, respectively. However, the whole-blood pH, as measured by a standard pH meter, was found to be 7.54 for both types of blood. The initial concentration of 2,3-diphosphoglycerate in sickle cell blood was about 30% higher, but it was depleted much faster during incubation than that in normal blood. The difference in intracellular pH between these two types of blood samples remained constant during incubation, even after depletion of 2,3-diphosphoglycerate. These results suggest that there are differences in intracellular environment between normal and sickle cell blood. Thus, 31P nuclear magnetic resonance spectroscopy provides a fast, direct, continuous, and noninvasive way to monitor the intracellular environment of intact erythrocytes.

Thermotropic behavior of some fluorodimyristoylphosphatidylcholines

The thermotropic behavior of three fluorinated phospholipids has been studied by means of high-sensitivity differential scanning calorimetry. The three lipids are 1,2-di(X,X-difluoromyristovyl)phosphatidylcholine with X = 4,8, or 12. The compound with X = 4 has a higher transition temperature than dimyristoylphosphatidylcholine whereas the other two have lower values. All three lipids have transition enthalpies approximately twice that of the unsubstituted lipid. It was found the substituted lipids form strikingly nonideal mixtures with the parent compound. In view of these observations it is evident that results obtained using these or related compounds as probes of bilayer or membrane behavior must be interpreted with due caution. Some of the properties exhibited by geminal fluorine atoms in fluorinated phospholipids appear to be similar to those of cis double bonds in lipids.

Replication of the genes coding for 5 S RNA in synchronized HeLa cells

The duplication of the genes coding for 5-S RNA has been followed during the S phase of HeLa cell cultures synchronized by mitotic detechment. Replication was analyzed by exposing the cultures to bromodeoxyuridine (BrdUrd) for 3 h at successive intervals and analyzing the DNA product in CsCl density gradients. DNA containing the 5-S genes was detected in the gradients by molecular hybridization using purified 125I-labeled 5 S RNA. In addition, as an internal marker of S phase chronology, late DNA replication was followed by examining the incorporation of [3H]thymidine into repetitive DNA (C0t less than 0.01 fraction). The results indicated that greater than 85% of the cells in the culture were synchronously dividing and that greater than 80% of the 5-S genes replicate in the first half of S phase, whereas the rapidly reassociating fraction of the DNA replicates in the second half of S phase.

Tertiary structure variability within the quaternary states of hemoglobin: a spin label study

Using variable temperature techniques, the spin label spectral resolution of hemoglobin labeled at the beta93 cysteines with N-(1-oxyl-2,2,6,6-tetramethyl-4-piperidinyl)iodonacetamide has been greatly enhanced. The effects of different ligands, inositol hexaphosphate, pH and salt concentration upon spin labeled ferrous and ferric hemoglobin indicate that the beta chain tertiary structure exhibits considerable variability within the oxy and deoxy quaternary structures. From these studies ligand and spin state changes both appear to be of significance in producing structural changes; binding of inositol hexaphosphate then produces further structural changes secondary in amplitude.