JM2, encoding a fork head-related protein, is mutated in X-linked autoimmunity-allergic disregulation syndrome

X-linked autoimmunity-allergic disregulation syndrome (XLAAD) is an X-linked recessive immunological disorder characterized by multisystem autoimmunity, particularly early-onset type 1 diabetes mellitus, associated with manifestations of severe atopy including eczema, food allergy, and eosinophilic inflammation. Consistent with the allergic phenotype, analysis of two kindreds with XLAAD revealed marked skewing of patient T lymphocytes toward the Th2 phenotype. Using a positional-candidate approach, we have identified in both kindreds mutations in JM2, a gene on Xp11.23 that encodes a fork head domain-containing protein. One point mutation at a splice junction site results in transcripts that encode a truncated protein lacking the fork head homology domain. The other mutation involves an in-frame, 3-bp deletion that is predicted to impair the function of a leucine zipper dimerization domain. Our results point to a critical role for JM2 in self tolerance and Th cell differentiation.

The effect of HFE genotypes on measurements of iron overload in patients attending a health appraisal clinic

BACKGROUND

The gene that causes most cases of hereditary hemochromatosis is designated HFE. Three mutations exist at this locus at a relatively high gene frequency.

OBJECTIVE

To determine the gene frequency of the three HFE mutations and to relate genotypes to various clinical and laboratory variables.

DESIGN

Observational study.

SETTING

Health appraisal clinic.

PATIENTS

10,198 adults who registered for health appraisal and consented to DNA examination for hemochromatosis. Consenting patients were slightly older and had attained a slightly higher educational level than nonconsenting patients.

MEASUREMENTS

Extensive medical history and laboratory tests, including complete blood count, transferrin saturation, and other chemistries; serum ferritin levels; and HFE genotype.

RESULTS

In white participants, the gene frequencies were 0.063 for the C282Y mutation, 0.152 for the H63D mutation, and 0.016 for the S65C mutation. Gene frequencies were lower in other ethnic groups. In participants with HFE mutations, the average serum transferrin saturation and ferritin levels were slightly increased, as were mean hemoglobin levels and mean corpuscular volume. A transferrin saturation of 50% had a sensitivity of only 0.52 (95% CI, 0.345 to 0.686) and a specificity of 0.908 (CI, 0.902 to 0.914) for detection of homozygosity. A ferritin level of 200 microg/L in women and 250 microg/L in men had a sensitivity of 0.70 (CI, 0.540 to 0.854) and a specificity of 0.803 (CI, 0.796 to 0.811). The prevalence of iron deficiency anemia was lower in women who carried HFE mutations.

CONCLUSIONS

Screening for transferrin saturation and ferritin levels does not detect all homozygotes for the major hemochromatosis mutation. Heterozygotes for HFE mutations had a lower prevalence of iron deficiency anemia.

Ca(2+)-dependent gene expression mediated by MEF2 transcription factors

Ca(2+) induction of a subset of cellular and viral immediate-early activation genes in lymphocytes has been previously mapped to response elements recognized by the MEF2 family of transcription factors. Here, we demonstrate that Ca(2+) activation of MEF2 response elements in T lymphocytes is mediated in synergy by two Ca(2+)/calmodulin-dependent enzymes, the phosphatase calcineurin, and the kinase type IV/Gr (CaMKIV/Gr), which promote transcription by the MEF2 family members MEF2A and MEF2D. Calcineurin up-regulates the activity of both factors by an NFAT-dependent mechanism, while CaMKIV/Gr selectively and independently activates MEF2D. These results identify MEF2 proteins as effectors of a pathway of gene induction in T lymphocytes which integrates diverse Ca(2+) activation signals and may be broadly operative in several tissues.

Production of unmodified human adult hemoglobin in Escherichia coli

We have constructed a plasmid (pHE2) in which the synthetic human alpha- and beta-globin genes and the methionine aminopeptidase (Met-AP) gene from Escherichia coli are coexpressed under the control of separate tac promoters. The Hbs were expressed in E. coli JM109 and purified by fast protein liquid chromatography, producing two major components, a and b. Electrospray mass spectrometry shows that at least 98% and about 90% of the expressed alpha and beta chains of component a, respectively, have the expected masses. The remaining 10% of the beta chain in component a corresponds in mass to the beta chain plus methionine. In component b, both alpha and beta chains have the correct masses without detectable N-terminal methionine (< 2%). These results have been confirmed by Edman degradation studies of the amino-terminal sequences of the alpha and beta chains of these two recombinant Hb (rHb) samples. rHbs from components a and b exhibit visible optical spectra identical to that of human normal adult Hb (Hb A). Component a and Hb A have very similar oxygen-binding properties, but component b shows somewhat altered oxygen binding, especially at low pH values. 1H-NMR spectra of component a and Hb A are essentially identical, whereas those of component b exhibit altered ring current-shifted and hyperfine-shifted proton resonances, indicating altered heme conformation in the beta chain. These altered resonance patterns can be changed to those of Hb A by converting component b to the ferric state and then to the deoxy state and finally back to either the carbonmonoxy or oxy form. Thus, our E. coli expression system produces native, unmodified Hb A in high yield and can be used to produce desired mutant Hbs.

A unique phosphorylation-dependent mechanism for the activation of Ca2+/calmodulin-dependent protein kinase type IV/GR

The activity of the Ca2+/calmodulin-dependent protein kinase IV/Gr (CaMKIV/Gr) is shown to be strictly regulated by phosphorylation of three residues both in vitro and in response to antigen receptor-mediated signaling in lymphocytes. One residue, Thr-200, is indispensable for enhancement of Ca2+/calmodulin-dependent basal activity by CaMKIV/Gr kinase. This event requires Ca2+/calmodulin in the full-length CaMKIV/Gr but is Ca2+/calmodulin-independent when a truncated version of CaMKIV/Gr is used as a substrate (DeltaCaMKIV/Gr1-317 (Delta1-317)). The other two residues, Ser12 and Ser13, are apparently autophosphorylated by the Ca2+/calmodulin-bound CaMKIV/Gr. Phosphorylation of neither Ser12-Ser13 nor Thr312 (the residue in a homologous position to Thr286 of CaMKIIalpha influences the development of Ca2+/calmodulin-independent activity or any other property of CaMKIV/Gr examined. Similarly, removal of the NH2-terminal 20 amino acids has no effect on the activation or function of CaMKIV/Gr. However, mutation of both Ser12 and Ser13 residues to Ala in Delta1-317 completely abrogates activity, while individual substitutions have no effect. These results indicate that the NH2-terminal Ser cluster mediates a novel type of intrasteric inhibition and suggest that three events are required for CaMKIV/Gr activation: 1) Ca2+/calmodulin binding; 2) phosphorylation of the Ca2+/calmodulin-bound enzyme on Thr200 by a Ca2+/calmodulin-dependent protein kinase kinase; and 3) autophosphorylation of Ser12-Ser13. This three-step requirement is unique among the multifunctional Ca2+/calmodulin-dependent kinases.

Production of human normal adult and fetal hemoglobins in Escherichia coli

A hemoglobin expression system in Escherichia coli is described. In order to produce authentic human hemoglobin, we need to co-express both methionine aminopeptidase and globin genes under the control of a strong promoter. We have constructed three plasmids, pHE2, pHE4 and pHE7, for the expression of human normal adult hemoglobin and a plasmid, pHE9, for the expression of human fetal hemoglobin, in high yields. The globin genes can be derived from either synthetic genes or human globin cDNAs. The extra amino-terminal methionine residues of the expressed globins can be removed by the co-expressed methionine aminopeptidase. The heme is inserted correctly into the expressed alpha-globin from our expression plasmids. A fraction (approximately 25%) of the heme is not inserted correctly into the expressed beta- or gamma-globin. However, the incorrectly inserted hemes can be converted into the correct conformation by carrying out a simple oxidation-reduction process on the purified hemoglobin molecule. We have investigated the functional properties of the expressed hemoglobins by measuring their oxygen-binding properties and their structural features by obtaining their 1H-NMR spectra. Our results show that authentic human normal adult and fetal hemoglobins can be produced from our expression plasmids in E. coli and in high yields. Our expression system allows us to design and to produce any recombinant hemoglobins needed for our research on the structure-function relationship in 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.

Conservation of the Caenorhabditis elegans timing gene clk-1 from yeast to human: a gene required for ubiquinone biosynthesis with potential implications for aging

Mutations in the Caenorhabditis elegans gene clk-1 have a major effect on slowing development and increasing life span. The Saccharomyces cerevisiae homolog COQ7 encodes a mitochondrial protein involved in ubiquinone biosynthesis and, hence, is required for respiration and gluconeogenesis. In this study, RT-PCR and 5' RACE were used to isolate both human and mouse clk-1/COQ7 homologs. Human CLK-1 was mapped to Chr 16(p12-13.1) by Radiation Hybrid (RH) and fluorescence in situ hybridization (FISH) methods. The number and location of human CLK1 introns were determined, and the location of introns II and IV are the same as in C. elegans. Northern blot analysis showed that three different isoforms of CLK-1 mRNA are present in several tissues and that the isoforms differ in the amount of expression. The functional equivalence of human CLK-1 to the yeast COQ7 homolog was tested by introducing either a single or multicopy plasmid containing human CLK-1 cDNA into yeast coq7 deletion strains and assaying for growth on a nonfermentable carbon source. The human CLK-1 gene was able to functionally complement yeast coq7 deletion mutants. The protein similarities and the conservation of function of the CLK-1/clk-1/COQ7 gene products suggest a potential link between the production of ubiquinone and aging.

A test of the role of the proximal histidines in the Perutz model for cooperativity in haemoglobin

Human haemoglobin has long been a paradigm for cooperative ligand binding and allostery. Through analysis of the crystal structures of deoxyhaemoglobin and liganded haemoglobin, Perutz proposed a model for cooperativity in which the bond between the proximal histidine and the protein couples haem rearrangements to protein structure rearrangements. Here we test this model by deleting the bonds between the histidine imidazole side chain and the polypeptide. This detachment method allows us to determine directly the contribution of proximal histidine coupling to cooperativity of distal ligand binding. Proximal detachment significantly increases ligand affinity, reduces cooperativity, and prevents quaternary structure switching, in accord with the Perutz model. Residual cooperativity indicates that additional haem communication pathways exist that do not involve the proximal histidine coupling mechanism.

NMR reveals hydrogen bonds between oxygen and distal histidines in oxyhemoglobin

Compared with free heme, the proteins hemoglobin (Hb) and myoglobin (Mb) exhibit greatly enhanced affinity for oxygen relative to carbon monoxide. This physiologically vital property has been attributed to either steric hindrance of CO or stabilization of O(2) binding by a hydrogen bond with the distal histidine. We report here the first direct evidence of such a hydrogen bond in both alpha- and beta-chains of oxyhemoglobin, as revealed by heteronuclear NMR spectra of chain-selectively labeled samples. Using these spectra, we have assigned the imidazole ring (1)H and (15)N chemical shifts of the proximal and distal histidines in both carbonmonoxy- and oxy-Hb. Because of their proximity to the heme, these chemical shifts are extremely sensitive to the heme pocket conformation. Comparison of the measured chemical shifts with values predicted from x-ray structures suggests differences between the solution and crystal structures of oxy-Hb. The chemical shift discrepancies could be accounted for by very small displacements of the proximal and distal histidines. This suggests that NMR could be used to obtain very high-resolution heme pocket structures of Hb, Mb, and other heme proteins.

Chain-selective isotopic labeling for NMR studies of large multimeric proteins: application to hemoglobin

Multidimensional, multinuclear NMR has the potential to elucidate the mechanisms of allostery and cooperativity in multimeric proteins under near-physiological conditions. However, NMR studies of proteins made up of non-equivalent subunits face the problem of severe resonance overlap, which can prevent the unambiguous assignment of resonances, a necessary step in interpreting the spectra. We report the application of a chain-selective labeling technique, in which one type of subunit is labeled at a time, to carbonmonoxy-hemoglobin A (HbCO A). This labeling method can be used to extend previous resonance assignments of key amino acid residues, which are important to the physiological function of hemoglobin. Among these amino acid residues are the surface histidyls, which account for the majority of the Bohr effect. In the present work, we report the results of two-dimensional heteronuclear multiple quantum coherence (HMQC) experiments performed on recombinant (15)N-labeled HbCO A. In addition to the C2-proton (H epsilon(1)) chemical shifts, these spectra also reveal the corresponding C4-proton (H delta(2)) resonances, correlated with the N epsilon(2) and N delta(1) chemical shifts of all 13 surface histidines per alpha beta dimer. The HMQC spectrum also allows the assignment of the H delta(1), H epsilon(1), and N epsilon(1) resonances of all three tryptophan residues per alpha beta dimer in HbCO A. These results indicate that heteronuclear NMR, used with chain-selective isotopic labeling, can provide resonance assignments of key regions in large, multimeric proteins, suggesting an approach to elucidating the solution structure of hemoglobin, a protein with molecular weight 64.5 kDa.

Assessment of roles of surface histidyl residues in the molecular basis of the Bohr effect and of beta 143 histidine in the binding of 2,3-bisphosphoglycerate in human normal adult hemoglobin

Site-directed mutagenesis has been used to construct two mutant recombinant hemoglobins (rHbs), rHb(betaH116Q) and rHb(betaH143S). Purified rHbs were used to assign the C2 proton resonances of beta116His and beta143His and to resolve the ambiguous assignments made over the past years. In the present work, we have identified the C2 proton resonances of two surface histidyl residues of the beta chain, beta116His and beta143His, in both the carbonmonoxy and deoxy forms, by comparing the proton nuclear magnetic resonance (NMR) spectra of human normal adult hemoglobin (Hb A) with those of rHbs. Current assignments plus other previous assignments complete the assignments for all 24 surface histidyl residues of human normal adult hemoglobin. The individual pK values of 24 histidyl residues of Hb A were also measured in deuterium oxide (D(2)O) in 0.1 M N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid (HEPES) buffer in the presence of 0.1 M chloride at 29 degrees C by monitoring the shifts of the C2 proton resonances of the histidyl residues as a function of pH. Among those surface histidyl residues, beta146His has the biggest contribution to the alkaline Bohr effect (63% at pH 7.4), and beta143His has the biggest contribution to the acid Bohr effect (71% at pH 5.1). alpha20His, alpha112His, and beta117His have essentially no contribution; alpha50His, alpha72His, alpha89His, beta97His, and beta116His have moderate positive contributions; and beta2His and beta77His have a moderate negative contribution to the Bohr effect. The sum of the contributions from 24 surface histidyl residues accounted for 86% of the alkaline Bohr effect at pH 7.4 and about 55% of the acid Bohr effect at pH 5.1. Although beta143His is located in the binding site for 2,3-bisphosphoglycerate (2,3-BPG) according to the crystal structure of deoxy-Hb A complexed with 2, 3-BPG, beta143His is not essential for the binding of 2,3-BPG in the neutral pH range according to the proton NMR and oxygen affinity studies presented here. With the accurately measured and assigned individual pK values for all surface histidyl residues, it is now possible to evaluate the Bohr effect microscopically for novel recombinant Hbs with important functional properties, such as low oxygen affinity and high cooperativity. The present study further confirms the importance of a global electrostatic network in regulating the Bohr effect of the hemoglobin molecule.

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.

Activation protein 1-dependent transcriptional activation of interleukin 2 gene by Ca2+/calmodulin kinase type IV/Gr

The Ca2+/calmodulin-dependent protein kinase (CaMK) type IV/Gr is selectively expressed in T lymphocytes and is activated after signaling via the T cell antigen receptor (TCR), indicating that it mediates some of the Ca(2+)-dependent transcriptional events that follow TCR engagement. Here we show that CaMKIV/Gr induces the transcription factor activation protein 1 (AP-1) alone or in synergy with T cell mitogens and with the p21ras oncoprotein. CaMKIV/ Gr signaling is associated with transcriptional activation of c-fos but is independent of p21ras or calcineurin. AP-1 is an integral component of the nuclear factor of activated T cells (NFAT) transcriptional complex, which is required for interleukin 2 gene expression in T cells. We demonstrate that CaMKIV/Gr reconstitutes the capacity of the cytosolic component of NFAT to direct transcription from NFAT sites in non-T cells. These results reveal a central role for CaMKIV/Gr as a Ca(2+)-regulated activator of gene transcription in T lymphocytes.

Contribution of surface histidyl residues in the alpha-chain to the Bohr effect of human normal adult hemoglobin: roles of global electrostatic effects

We have applied site-directed mutagenesis to our Escherichia coli hemoglobin expression plasmid and constructed five recombinant mutant hemoglobins (r Hbs): r Hb(alpha20His-->Gln or alpha:H20Q); r Hb(alpha:H50Q); r Hb(alpha:H72Q); r Hb(alpha:H89Q); and r Hb(alpha:H112Q). We have constructed these r Hbs to help us assess the contribution of the surface histidyl residues in the alpha-chain to the alkaline Bohr effect of human normal adult hemoglobin (Hb A). In our laboratory, we have monitored the variation of proton nuclear magnetic resonances arising from the C2 protons of the histidyl residues of Hb A as a function of pH and buffer conditions. Several of these resonances have been assigned to the individual histidyl residues on the surface of the hemoglobin molecule using naturally occurring mutant hemoglobins and chemically modified hemoglobins. In the present work, we have identified the C2 proton resonances of five surface histidyl residues of the alpha-chain, alpha20, alpha50, alpha72, alpha89, and alpha112, in both the carbonmonoxy and deoxy forms, by comparing the proton nuclear magnetic resonance spectra of Hb A with those of the r Hbs. For the assignment of the C2 proton resonances of alpha20His and alpha112His, we have used combinations of mutations to compensate for the spectral perturbations resulting from the single mutations, which obscure the resonance assignment. On the basis of the new findings, in solvent containing 0.1 M chloride, the overall contributions from surface histidyl residues of both the alpha- and beta-chain and from other previously identified alkaline Bohr groups account for approximately 75% of the observed Bohr effect at pH 7.3 (the maximum Bohr effect under the prescribed solvent conditions). Our results show that some histidyl residues contribute to the Bohr effect and some oppose the net Bohr effect. In some cases, the addition of anions can diminish or reverse the contributions of specific histidyl residues to the overall Bohr effect. Thus, the Bohr effect, a heterotropic effect, depends on the intricate arrangement and interactions of all hydrogen and anion binding sites in the hemoglobin molecule. It is an excellent example of global electrostatic effects in proteins.

A proton nuclear Overhauser effect investigation of the subunit interfaces in human normal adult hemoglobin

High-resolution proton nuclear magnetic resonance spectroscopy and nuclear Overhauser effects for the low-field exchangeable proton resonances of human normal adult hemoglobin in aqueous solvents are being used to confirm and extend the assignments of these resonances to specific protons at the intersubunit interfaces of the molecule. Most of these exchangeable proton resonances of human normal adult hemoglobin have been found to be absent in the spectra of isolated alpha or beta subunits. This finding indicates that they are specific spectral markers for the quaternary structure of the hemoglobin tetramer. Based on the nuclear Overhauser effect results, we have assigned the exchangeable proton resonance at +7.4 ppm downfield from H2O to the hydrogen-bonded proton between alpha 103(G10)His and beta 108(G10)Asn at the alpha 1 beta 1 interface. The nuclear Overhauser effect results have also confirmed the assignments of the exchangeable proton resonances at +9.4 and +8.2 ppm downfield from H2O previously proposed by workers in this laboratory based on a comparison of human normal adult hemoglobin and appropriate mutant hemoglobins. This independent confirmation of previously proposed assignments is necessary in view of the possible long-range conformational effects of single amino-acid substitutions in mutant hemoglobin molecules.

Mutations of CTSK result in pycnodysostosis via a reduction in cathepsin K protein

Pycnodyostosis, an autosomal recessive osteosclerosing skeletal disorder, has recently been shown to result from mutations in the cathepsin K gene. Cathepsin K, a lysosomal cysteine protease with an abundant expression in osteoclasts, has been implicated in osteoclast-mediated bone resorption and remodeling. DNA sequence analysis of the cathepsin K gene in a nonconsanguineous family demonstrated compound heterozygozity for mutations in two affected siblings. We have identified a missense mutation with a single base G-->A transition at cDNA nucleotide 236, resulting in conversion of a conserved glycine to a glutamine residue (G79E). The other mutation is an A-->T transition at nucleotide 154, leading to the substitution of a lysine residue by a STOP codon (K52X) predicting premature termination of the precursor cathepsin K polypeptide. Sequencing of genomic and cDNAs from the parents demonstrated that the missense mutation was inherited from the father and the nonsense mutation from the mother. Protein expression in both affected children was virtually absent, while in the parents was reduced by 50-80% compared with controls. The protein studies demonstrate that even significantly reduced cathepsin K levels do not have any phenotypic effect, whereas absent cathepsin K results in pycnodysostosis.

Determination of partial solubility parameters of lactose by gas-solid chromatography

On the basis of the Snyder/Karger-Hansen interaction model, where delta EA = Vi(delta di delta dj + delta pi delta pi + delta hi delta nj), the partial solubility parameters of a solid used as the stationary phase may be determined through gas-solid chromatography by null-injection of solutes with known solubility parameters. Using n-decane, acetonitrile, and 1-propanol as molecular probes, the values found for unhydrated lactose were 9.6, 12.8, 11.3, and 19.5 (cal1/2/cm3/2) for delta d, delta p, delta h, and delta t, respectively; relative standard errors were better than 3%. The choice and the minimum number of the best molecular probes were determined by optimization of the experimental matrix according to the D-criterion, which permits considerable reduction of experimental time yet enhances total precision.

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...

Effects of substitutions of lysine and aspartic acid for asparagine at beta 108 and of tryptophan for valine at alpha 96 on the structural and functional properties of human normal adult hemoglobin: roles of alpha 1 beta 1 and alpha 1 beta 2 subunit interfaces in the cooperative oxygenation process

Using our Escherichia coli expression system, we have produced five mutant recombinant (r) hemoglobins (Hbs): r Hb (alpha V96 W), r Hb Presbyterian (beta N108K), r Hb Yoshizuka (beta N108D), r Hb (alpha V96W, beta N108K), and r Hb (alpha V96W, beta N108D). These r Hbs allow us to investigate the effect on the structure-function relationship of Hb of replacing beta 108Asn by either a positively charged Lys or a negatively charged Asp as well as the effect of replacing alpha 96Val by a bulky, nonpolar Trp. We have conducted oxygen-binding studies to investigate the effect of several allosteric effectors on the oxygenation properties and the Bohr effects of these r Hbs. The oxygen affinity of these mutants is lower than that of human normal adult hemoglobin (Hb A) under various experimental conditions. The oxygen affinity of r Hb Yoshizuka is insensitive to changes in chloride concentration, whereas the oxygen affinity of r Hb Presbyterian exhibits a pronounced chloride effect. r Hb Presbyterian has the largest Bohr effect, followed by Hb A, r Hb (alpha V96W), and r Hb Yoshizuka. Thus, the amino acid substitution in the central cavity that increases the net positive charge enhances the Bohr effect. Proton nuclear magnetic resonance studies demonstrate that these r Hbs can switch from the R quaternary structure to the T quaternary structure without changing their ligation states upon the addition of an allosteric effector, inositol hexaphosphate, and/or by reducing the temperature. r Hb (alpha V96W, beta N108K), which has the lowest oxygen affinity among the hemoglobins studied, has the greatest tendency to switch to the T quaternary structure. The following conclusions can be derived from our results: First, if we can stabilize the deoxy (T) quaternary structure of a hemoglobin molecule without perturbing its oxy (R) quaternary structure, we will have a hemoglobin with low oxygen affinity and high cooperativity. Second, an alteration of the charge distribution by amino acid substitutions in the alpha 1 beta 1 subunit interface and in the central cavity of the hemoglobin molecule can influence the Bohr effect. Third, an amino acid substitution in the alpha 1 beta 1 subunit interface can affect both the oxygen affinity and cooperativity of the oxygenation process. There is communication between the alpha 1 beta 1 and alpha 1 beta 2 subunit interfaces during the oxygenation process. Fourth, there is considerable cooperativity in the oxygenation process in the T-state of the hemoglobin molecule.

The Epstein-Barr virus-induced Ca2+/calmodulin-dependent kinase type IV/Gr promotes a Ca(2+)-dependent switch from latency to viral replication

The switch from latency to viral replication in Epstein-Barr virus (EBV)-transformed human B cells is mediated by Zta, the protein product of immediate-early EBV gene BZLF1. BZLF1 transcription is normally suppressed in EBV-transformed B cells but can be induced in some cell lines upon ligation of surface immunoglobulin by mechanisms that include the activation of Ca(2+)-dependent signaling pathways. The multifunctional Ca2+/calmodulin-dependent kinase type IV/Gr (CaMKIV/Gr) is normally absent in primary human B cells, but its expression is induced by the EBV oncoprotein LMP1 in the course of B-cell growth transformation by EBV. In this study, we demonstrate that activated CaMKIV/Gr induces transcription from the BZLF1 promoter and upregulates the expression of Zta in permissive cells. Transcriptional activation of the BZLF1 promoter by CaMKIV/Gr is dependent on the CREB/AP1 binding element ZII and is greatly augmented by the Ca2+/calmodulin-dependent phosphatase calcineurin. These results outline a virus-regulated mechanism involving CaMKIV/Gr which promotes transition from latency to productive viral replication in response to Ca(2+)-mobilizing extracellular signals.

Roles of the beta 146 histidyl residue in the molecular basis of the Bohr effect of hemoglobin: a proton nuclear magnetic resonance study

Assessment of the roles of the carboxyl-terminal beta 146 histidyl residues in the alkaline Bohr effect in human normal adult hemoglobin by high-resolution proton nuclear magnetic resonance spectroscopy requires assignment of the resonances corresponding to these residues. Previous resonance assignments in low ionic strength buffers for the beta 146 histidyl residue in the carbonmonoxy form of hemoglobin have been controversial [see Ho and Russu (1987) Biochemistry 26, 6299-6305; and references therein]. By a careful spectroscopic study of human normal adult hemoglobin, enzymatically prepared des(His146 beta)-hemoglobin, and the mutant hemoglobins Cowtown (beta 146His----Leu) and York (beta 146His----Pro), we have resolved some of these conflicting results. By a close incremental variation of pH over a wide range in chloride-free 0.1 M N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid buffer, a single resonance has been found to be consistently missing in the proton nuclear magnetic resonance spectra of these hemoglobin variants. The spectra of each of these variants show additional perturbations; therefore, the assignment has been confirmed by an incremental titration of buffer conditions to benchmark conditions, i.e., 0.2 M phosphate, where the assignment of this resonance is unambiguous. The strategy of incremental titration of buffer conditions also allows extension of this resonance assignment to spectra taken in 0.1 M [bis(2-hydroxyethyl)amino]tris(hydroxymethyl)methane buffer. Participation of the beta 146 histidyl residues in the Bohr effect has been calculated from the pK values determined for the assigned resonances in chloride-free 0.1 M N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid buffer. Our results indicate that the contribution of the beta 146 histidyl residues is 0.52 H+/hemoglobin tetramer at pH 7.6, markedly less than the 0.8 H+/hemoglobin tetramer estimated by study of the mutant hemoglobin Cowtown (beta 146His----Leu) by Shih and Perutz [(1987) J. Mol. Biol. 195, 419-422]. We have found that at least two histidyl residues in the carbonmonoxy form of this mutant have pK values that are perturbed, and we suggest that these pK differences may in part account for this discrepancy. Furthermore, summation of the positive contribution of the beta 146 histidyl residues and the negative contribution of the beta 2 histidyl residues to the maximum Bohr effect measured in 0.1 M N-(2-hydroxyethyl)piperazine-N'-2-ethanesulfonic acid buffer suggests that additional sites in the hemoglobin molecule account for proton release upon ligation greater than the contribution of the beta 146 histidyl residues.(ABSTRACT TRUNCATED AT 400 WORDS)

Restoring allosterism with compensatory mutations in hemoglobin

Abnormal human hemoglobins (HBs) with amino acid substitutions in the alpha 1 beta 2 interface have very high oxygen affinity and greatly reduced cooperativity in O2 binding compared to normal human Hb. In such abnormal Hbs with mutations at position beta 99, the intersubunit hydrogen bonds between Asp-beta 99 and Tyr-alpha 42 and between Asp-beta 99 and Asn-alpha 97 are broken, thus destabilizing the deoxyquaternary structure of these Hbs. A molecular dynamics method has been used to design compensatory amino acid substitutions in these Hbs that can restore their allosteric properties. We have designed a compensatory mutation in a naturally occurring mutant Hb, Hb Kempsey (Asp-beta 99-->Asn), and have produced it using our Escherichia coli expression plasmid pHE2. We have determined the O2 binding properties of this recombinant double mutant Hb, Hb(Asp-beta 99-->Asn and Tyr-alpha 42-->Asp) and have used 1H NMR spectroscopy to investigate the tertiary structures around the heme groups and the quaternary structure in the alpha 1 beta 2 subunit interface. Our results clearly show that the Tyr-alpha 42-->Asp replacement can substantially compensate for the functional defect of Hb Kempsey caused by the Asp-beta 99-->Asn substitution. The structural and functional information derived from this recombinant Hb provides insights into the structural basis of allosterism and the design of compensatory amino acid substitutions to restore the functional properties of other abnormal HBs associated with hemoglobinopathies.

Distal ligand reactivity and quaternary structure studies of proximally detached hemoglobins

The linkage between the proximal histidines and the proximal polypeptide in normal adult human hemoglobin (Hb A) has been proposed to play a major role in transmitting allosteric effects between oxygen binding sites [Perutz, M. F. (1970) Nature 228, 726-734]. Here we present circular dichroism (CD), (1)H NMR, analytical ultracentrifugation, and stopped-flow kinetic data to better define the quaternary structure of hemoglobins in which the linkage between the proximal histidines and the polypeptide backbone has been broken [Barrick et al. Nat. Struct. Biol. 4, 78-83 (1997)] and to characterize the distal ligand binding properties of these proximally detached Hbs. CD spectroscopy indicates that rHb (alphaH87G) and rHb (alphaH87G/betaH92G) retain at least partial T-quaternary structure with distal ligand bound, whereas rHb (betaH92G) does not, consistent with (1)H NMR spectra. Analytical ultracentrifugation reveals significant tetramer dissociation in rHb (betaH92G) to be the likely cause of loss of T-state markers. These quaternary structure studies indicate that in distally liganded Hb, the T-state is compatible with proximal linkages in the beta- but not the alpha-chains. (1)H NMR titrations of rHb (alphaH87G) with n-butyl isocyanide demonstrate the alpha-chains to be of high affinity as compared with the beta-chains. Comparing ligand association and dissociation rates between the rHb (alphaH87G) variant with the T- and R-states of wild-type Hb A indicates that at the alpha-chains, carbon monoxide affinity is modulated entirely by the proximal linkage, rather than from distal interactions. Some residual allosteric interactions may remain operative at the beta-chains of rHb (alphaH87G).

WAXS studies of the structural diversity of hemoglobin in solution

Specific ligation states of hemoglobin are, when crystallized, capable of taking on multiple quaternary structures. The relationship between these structures, captured in crystal lattices, and hemoglobin structure in solution remains uncertain. Wide-angle X-ray solution scattering (WAXS) is a sensitive probe of protein structure in solution that can distinguish among similar structures and has the potential to contribute to these issues. We used WAXS to assess the relationships among the structures of human and bovine hemoglobins in different liganded forms in solution. WAXS data readily distinguished among the various forms of hemoglobins. WAXS patterns confirm some of the relationships among hemoglobin structures that have been defined through crystallography and NMR and extend others. For instance, methemoglobin A in solution is, as expected, nearly indistinguishable from HbCO A. Interestingly, for bovine hemoglobin, the differences between deoxy-Hb, methemoglobin and HbCO are smaller than the corresponding differences in human hemoglobin. WAXS data were also used to assess the spatial extent of structural fluctuations of various hemoglobins in solution. Dynamics has been implicated in allosteric control of hemoglobin, and increased dynamics has been associated with lowered oxygen affinity. Consistent with that notion, WAXS patterns indicate that deoxy-Hb A exhibits substantially larger structural fluctuations than HbCO A. Comparisons between the observed WAXS patterns and those predicted on the basis of atomic coordinate sets suggest that the structures of Hb in different liganded forms exhibit clear differences from known crystal structures.