Role of Borna disease virus in neuropsychiatric illnesses: are we inching closer?

The biological cause of psychiatric illnesses continues to be under intense scrutiny. Among the various neurotropic viruses, Borna disease virus (BDV) is another virus that preferentially targets the neurons of the limbic system and has been shown to be associated with behavioural abnormalities. Presence of various BDV markers, including viral RNA, in patients with affective and mood disorders have triggered ongoing debate worldwide regarding its aetiopathogenic relationship. This article analyses its current state of knowledge and recent advances in diagnosis in order to prove or refute the association of BDV in causation of human neuropsychiatric disorders. This emerging viral causative association of behavioural disorders, which seems to be inching closer, has implication not only for a paradigm shift in the treatment and management of neuropsychiatric illnesses but also has an important impact on the public health systems.

Cutaneous infection with Mycobacterium fortuitum: an unusual presentation

Cutaneous infection with rapidly growing mycobacteria is uncommon and its diagnosis can be missed unless there is strong clinical suspicion coupled with microbiological confirmation. We report a case of localized recurrent soft tissue swelling of the foot by Mycobacterium fortuitum in a healthy adult male. The case is being reported for its uncommon clinical presentation and the associated etiological agent. The patient recovered completely following therapy with amikacin and clarithromycin.

Anatomical and gene expression mapping of the ventral pallium in a three-dimensional model of developing human brain

Combining gene expression data with morphological information has revolutionized developmental neuroanatomy in the last decade. Visualization and interpretation of complex images have been crucial to these advances in our understanding of mechanisms underlying early brain development, as most developmental processes are spatially oriented, in topologically invariant patterns that become overtly distorted during brain morphogenesis. It has also become clear that more powerful methodologies are needed to accommodate the increasing volume of data available and the increasingly sophisticated analyses that are required, for example analyzing anatomy and multiple gene expression patterns at individual developmental stages, or identifying and analyzing homologous structures through time and/or between species. Three-dimensional models have long been recognized as a valuable way of providing a visual interpretation and overview of complex morphological data. We have used a recently developed method, optical projection tomography, to generate digital three-dimensional models of early human brain development. These models can be used both as frameworks, onto which normal or experimental gene expression data can be mapped, and as objects, within which topological morphological relationships can be investigated in silico. Gene expression patterns and selected morphological structures or boundaries can then be visualized individually or in different combinations in order to study their respective morphogenetic significance. Here, we review briefly the optical projection tomography method, placing it in the context of other methods used to generate developmental three dimensional models, and show the definition of some CNS anatomical domains within a Carnegie stage 19 human model. We also map the telencephalic EMX1 and PAX6 gene expression patterns to this model, corroborating for the first time the existence of a ventral pallium primordium in the telencephalon of human embryos, a distinct claustroamygdaloid histogenetic area comparable to the recently defined mouse primordium given that name [Puelles L, Kuwana E, Puelles E, Bulfone A, Shimamura K, Keleher J, Smiga S, Rubenstein JLR (2000) Pallial and subpallial derivatives in the embryonic chick and mouse telencephalon, traced by the expression of the genes Dlx-2, Emx-1, Nkx-2.1, Pax-6, and Tbr-1. J Comp Neurol 424:409-438; Puelles L, Martínez S, Martínez-de-la-Torre M, Rubenstein JLR (2004) Gene maps and related histogenetic domains in the forebrain and midbrain. In: The rat nervous system, 3rd ed (Paxinos G, ed), pp 3-25. San Diego: Academic Press].

Brain stem cavernoma excised by subtemporal-infratemporal approach

Brain stem cavernomas are most safely removed through the pial surface at which the cavernoma is surfacing. When a lower pontine or an upper medullary cavernoma comes to the surface of the anterior portion of the brain stem, it is difficult to reach by traditional approaches. We describe a case of mid- and lower pontine cavernoma, surfacing anteriorly, which was completely excised by the subtemporal-infratemporal approach. After making a small temporal craniotomy and a zygomatic osteotomy, the petrous carotid artery was mobilized anteriorly and the petroclival bone was drilled away to reach the anterior surface of the pons using the subtemporal-infratemporal approach. A small incision was made on the anterior surface of the pons, between the CN V and CN VI and the cavernoma was completely excised with the aid of the surgical microscope and the neuro-endoscope. Immediately after the operation, the patient had a complete abducens palsy and a mild increase of left hemiparesis, both of which resolved completely within 3 months. The patient returned to the full time work without any neurological deficit. A follow-up MRI 1 year later showed the complete excision of the cavernoma. The subtemporal-infratemporal approach is useful for anteriorly located mid to lower pontine and upper medullary cavernomas.

Brain-stem abscess successfully treated by microsurgical drainage: a case report

Brain-stem abscess is an uncommon condition associated with high mortality. The best method of treatment is not yet defined. It can be managed by medical treatment alone, stereotactic aspiration of the pus and medical treatment, or surgical excision/drainage of the abscess. We present a case of large brain-stem abscess, treated successfully by surgical drainage after the failure of medical treatment. The patient had a large brain-stem abscess extending from the mid-brain down to the lower pons. She was in a poor neurological condition pre-operatively, and was worsening despite intravenous antibiotics. The abscess was coming close to the surface in the lateral aspect of the mid-brain. The presumed source of infection was multiple dental abscesses. The brain-stem abscess was approached by a subtemporal transzygomatic approach and drained completely after making an incision on the lateral surface of the mid-brain. After the operation, the patient showed steady improvement. At six months after the surgery, the patient was fully conscious, talking fluently, and walking with the help of a walker. Her hemiparesis and co-ordination were improving. Surgical drainage of a brain-stem abscess is indicated when medical therapy fails. Proper anatomical knowledge of the brain-stem and the selection of appropriate surgical approach is important for safe drainage of the abscess.

Dural reconstruction with fascia, titanium mesh, and bone screws: technical note

OBJECTIVE

After the resection of cranial base tumors, there may not be enough free dural margin left for reconstruction after involved bone and dura have been removed. In such a situation, dural reconstruction becomes a problem. We propose a new technique of dural closure in such cases.

METHODS

A fascial graft is prepared from either fascia lata, abdominal fascia, pericranium, or temporal fascia and is trimmed to a size slightly larger than that of the dural defect. The fascial graft is placed over the dural defect and affixed to the underlying bone with a piece of titanium mesh, titanium screws, or both. The graft is then reinforced with fibrin glue.

RESULTS

This method of dural reconstruction has been used in five patients with basal meningiomas. Three were in the petromastoid area, and two were in the planum-ethmoid area. None of these patients experienced postoperative cerebrospinal fluid leak, and none experienced any complications related to the reconstruction.

CONCLUSION

This technique of dural reconstruction can be used in selected cases of basal tumors without enough free dural margin to sew into a fascial graft.

Expression and immunogenicity of human immunodeficiency virus type 1 Gag expressed by a replication-competent rhabdovirus-based vaccine vector

A replication-competent rhabdovirus-based vector expressing human immunodeficiency virus type 1 (HIV-1) Gag protein was characterized on human cell lines and analyzed for the induction of a cellular immune response in mice. We previously described a rabies virus (RV) vaccine strain-based vector expressing HIV-1 gp160. The recombinant RV was able to induce strong humoral and cellular immune responses against the HIV-1 envelope protein in mice (M. J. Schnell et al., Proc. Natl. Acad. Sci. USA 97:3544-3549, 2000; J. P. McGettigan et al., J. Virol. 75:4430-4434, 2001). Recent research suggests that the HIV-1 Gag protein is another important target for cell-mediated host immune defense. Here we show that HIV-1 Gag can efficiently be expressed by RV on both human and nonhuman cell lines. Infection of HeLa cells with recombinant RV expressing HIV-1 Gag resulted in efficient expression of HIV-1 precursor protein p55 as indicated by both immunostaining and Western blotting. Moreover, HIV-1 p24 antigen capture enzyme-linked immunosorbent assay and electron microscopy showed efficient release of HIV-1 virus-like particles in addition to bullet-shaped RV particles in the supernatants of the infected cells. To initially screen the immunogenicity of this new vaccine vector, BALB/c mice received a single vaccination with the recombinant RV expressing HIV-1 Gag. Immunized mice developed a vigorous CD8(+) cytotoxic T-lymphocyte response against HIV-1 Gag. In addition, 26.8% of CD8(+) T cells from mice immunized with RV expressing HIV-1 Gag produced gamma interferon after challenge with a recombinant vaccinia virus expressing HIV-1 Gag. These results further confirm and extend the potency of RV-based vectors as a potential HIV-1 vaccine.

Evidence of functional somatotopy in GPi from results of pallidotomy

The objective of this study was to explore the functional anatomy of the globus pallidus internus (GPi) by studying the effects of unilateral pallidotomy on parkinsonian 'off' signs and levodopa-induced dyskinesias (LID). We found significant positive correlations between the preoperative levodopa responsiveness of motor signs and the levodopa responsiveness of scores in timed tests (Core Assessment Program for Intracerebral Transplantations) in the contralateral limbs and the improvement in these scores after surgery, whereas there was no correlation with the improvement in LID. We also found a highly significant correlation (P: < 0.0001, r = 0.8) between the volume of the ventral lesion in the GPi and the improvement in LID in the contralateral limbs, whereas there was no correlation between the ventral volume and the improvement in parkinsonian 'off' signs. The volumes of the total lesion cylinder and the dorsal lesion did not correlate with the outcome of either dyskinesias or parkinsonian 'off' signs. The differential predictive value of levodopa responsiveness for the outcome of parkinsonian 'off' signs and LID and the different correlations of ventral lesion volume with dyskinesias and parkinsonian 'off' signs indicate that different anatomical or pathophysiological substrates may be responsible for the generation of parkinsonian 'off' signs and dyskinesias. Whereas cells in a wider area of the GPi may be implicated in parkinsonism, the ventral GPi seems to be crucial for the manifestation of LID. We suggest that our observations are additional proof of the functional somatotopy of the systems within the GPi that mediate parkinsonism and dyskinesias, especially along the dorsoventral trajectory used in pallidotomy. The outcome of pallidotomy in which the lesion involves the ventral and dorsal GPi could be the net effect of alteration in the activity of pathways which mediate different symptoms, and hence could be variable.

Triterpenoid saponins from the roots of tea plant (Camellia sinensis var. assamica)

Three olean-12-ene type triterpenoid saponins, named TR-saponins A, B and C, were isolated as methyl esters from tea roots (Camellia sinesis var. assamica) after treatment with diazomethane. Their structures were established as the methyl esters of 3-O-alpha-L-arabinopyranosyl (1-->3)-beta-D-glucuronopyranosyl-21, 22-di-O-angeloyl-R1-barrigenol-23-oic acid, 3-O-alpha-L-arabinopyranosyl (1-->3)-beta-D-glucuronopyranosyl-21-O-angeloyl-22-O-2-me thylbutanoyl-R1- barrigenol-23-oic acid and 3-O-alpha-L-arabinopyranosyl (1-->3)-beta-D-glucuronopyranosyl-16 alpha-O-acetyl-21-O-angeloyl-22-O-2-methylbutanoyl-R1-bar rigenol-23-oic acid, by extensive 1D and 2D-NMR as well as FABMS and HR-MS analyses.

Two mechanisms for tumor evasion of preexisting cytotoxic T-cell responses: lessons from recurrent tumors

Tumors evade host immunity at both the induction and effector phases Most studies have focused on tumor evasion at the induction phase, and, due in part to poor antitumor CTL responses to most tumors, the mechanism for evasion of CTL effector function is less clear. Here we have taken advantage of the strong CTL responses to a costimulator B7-1-transfected tumor to study the mechanism for tumor evasion of preexisting host immunity. We have investigated six independent recurrent tumors isolated from mice that were challenged with and had rejected B7-1-transfected J558 (J558-B7) tumors. Because the mice had developed strong antitumor CTL responses, these recurrent tumors must have evaded preexisting antitumor CTLs. Indeed, whereas the parental J558-B7 cell line is efficiently lysed by the ex vivo tumor-infiltrating lymphocytes, all of the recurrent tumors are resistant to such lysis. Interestingly, the recurrent tumors can be divided into two groups. The group 1 tumors have vastly reduced levels of cell surface MHC class I with a concurrent reduction in the expression of multiple genes devoted to MHC class I antigen presentation. In contrast, the group 2 tumors have lost the expression of costimulatory molecule B7-1 while retaining cell surface MHC class I and expression of all antigen presentation genes studied. These results demonstrate that tumors can evade preexisting CTLs either by avoiding presentation of the tumor antigen or, surprisingly, by down-regulation of costimulatory molecules. The paradoxical requirements of both antigen and costimulatory molecules at the effector phase raised an interesting question on the nature of antitumor immunity.

Micropropagation and in vitro flowering of Rauvolfia tetraphylla; a potent source of anti-hypertension drugs

A simple protocol for in vitro mass multiplication of Rauvolfia tetraphylla (Apocynaceae) has been developed. The endophytic microflora was controlled by adopting integrated measures. Multiple shoot development was achieved on MS + Kin (0.1-0.2 mg/l) + BAP (0.4-0.5 mg/l) media. Rooting from in vitro shoots occurred on NAA containing media. In vitro flowering was induced in shoot multiplication media.

Cytotoxic T lymphocytes to an unmutated tumor rejection antigen P1A: normal development but restrained effector function in vivo

Unmutated tumor antigens are chosen as primary candidates for tumor vaccine because of their expression on multiple lineages of tumors. A critical issue is whether unmutated tumor antigens are expressed in normal cells, and if so, whether such expression imposes special restrictions on cytotoxic T lymphocyte (CTL) responses. In this study, we use a transgenic approach to study the development and effector function of T cells specific for P1A, a prototypical unmutated tumor antigen. We report here that although P1A is expressed at low levels in normal tissues, including lymphoid tissues, the P1A-specific transgenic T cells develop normally and remain highly responsive to the P1A antigen. The fact that transgenic expression of P1A antigen in the thymus induces T cell clonal deletion demonstrates that normal hematopoietic cells can process and present the P1A antigen and that P1A-specific T cells are susceptible to clonal deletion. By inference, P1A-specific T cells must have escaped clonal deletion due to low expression of P1A in the thymus. Interestingly, despite the fact that an overwhelming majority of T cells in the T cell receptor for antigen (TCR)-transgenic mice are specific for P1A, these mice are no more resistant to a P1A-expressing plasmocytoma than nontransgenic littermates. Moreover, when the same TCR-transgenic mice were challenged simultaneously with B7-1(+) and B7-1(-) tumors, only B7-1(+) tumors were rejected. Therefore, even though P1A can be a tumor rejection antigen, the effector function of P1A-specific CTL is restrained in vivo. These results have important implications for the strategy of tumor immunotherapy.

An economic evaluation of patch testing in the diagnosis and management of allergic contact dermatitis

BACKGROUND

A previous retrospective study indicated that patch testing is cost-effective and well accepted by patients.

OBJECTIVE

The objective of this observational prospective study was to show the cost-effectiveness of patch testing in patients suspected of allergic contact dermatitis (ACD) and to determine the order in which different severity groups rank in terms of cost-effectiveness.

METHODS

This observational study was conducted in 567 patients from 10 investigator sites over a period of 1 year. All patients with a suspicion of contact allergy who exhibited at least moderate disease activity were included in the study and were stratified according to disease severity and whether or not they were patch tested. In each severity category, the cost-effectiveness of patch testing was evaluated. Patients who were ruled out for contact allergy by the first 6 months after admission were excluded. A validated dermatology-specific quality of life instrument was administered to all the patients at entrance into the study and at 6 and 12 months after that. The cost-effectiveness analysis is shown using a decision analysis model.

RESULTS

Patch testing was performed on 22% of patients with mild disease, 41% of patients with moderate disease, and 50% of patients with severe disease. As a result of changes made in their lifestyle, 66% in the patch-tested group and 51% in the non-patch-tested group reported 75% or more improvement in disease symptoms after 6 months. Early confirmation of diagnosis helped reduce the prediagnosis costs of treatment, which was mostly based on preliminary diagnosis. The greatest quality of life benefits from patch testing, relative to no patch testing, occurred in subjects with recurrent or chronic ACD.

CONCLUSION

Patch testing is most cost-effective and reduces the cost of therapy in patients with severe ACD.

Maturation of cytotoxic T lymphocytes against a B7-transfected nonmetastatic tumor: a critical role for costimulation by B7 on both tumor and host antigen-presenting cells

It is generally believed that CTLs mature in lymphoid organs and then migrate into target tissues to execute their effector functions. This notion, however, is based on studies using antigens that are readily localized in the lymphoid tissue, such as viruses and allogeneic transplants. The site for maturation of CTLs for nonmetastatic tumors has not been determined. Because nonmetastatic tumor cells are not localized in lymphoid tissues, it is questionable whether such tumors are efficient inducers of antitumor CTLs. Here, we report that a nonmetastatic B7+ plasmacytoma induces strong effector CTL response. Thus, it is possible to induce CTLs with strong ex vivo CTL activity in the absence of tumor metastasis. In addition, a detailed kinetic analysis of CD8 T cell recruitment and maturation of CTL activity suggests that antitumor CTLs mature within the tumor rather than in the lymphoid tissues. Interestingly, despite B7-1 expression on tumor cells, induction of effector CTLs also requires costimulation by B7 on host antigen-presenting cells. These findings have important implications for tumor gene therapy and for understanding the mechanism of CTL induction in vivo.

The use of decision-analytical modelling in economic evaluation of patch testing in allergic contact dermatitis

OBJECTIVE

The objective of this observational prospective study was to demonstrate the cost effectiveness of patch testing in patients suspected of allergic contact dermatitis (ACD) and to determine the order in which different severity groups rank in terms of cost effectiveness.

DESIGN AND SETTING

This observational study was conducted on 567 patients from 10 investigator sites in the US over a period of 1 year. All patients with a suspicion of contact allergy who exhibited at least moderate disease activity were included in the study and were stratified according to disease severity and whether or not they were patch tested. In each severity category, the cost effectiveness of patch testing was evaluated. Patients who were ruled out for contact allergy (without the use of patch test) by the first 6 months after admission were excluded. A validated dermatology-specific quality of life (DSQL) instrument was administered to all patients at the start of the study, and at 6 and 12 months thereafter. The cost-effectiveness analysis is demonstrated using a decision-analytical model. Costs included office visits and prescription costs without generic substitution. The cost of patch testing was not included due to the large variation in price among commercially available products.

MAIN OUTCOME MEASURES AND RESULTS

Patch testing was performed on 22% of patients with mild disease, 41% of patients with moderate disease and 50% of those with severe disease. There was a significant difference between the patch-tested and non-patch-tested groups in terms of the time to obtain a confirmed diagnosis (medians = 8 and 175 days, respectively) and a significant difference in the ratio of patients who had a confirmed diagnosis (88 and 69%, respectively). As a result of changes made in their lifestyle, 66% of patients in the patch-tested group and 51% in the non-patch-tested group reported 75% or more improvement in their disease symptoms after 6 months. Early confirmation of diagnosis helped reduce the prediagnosis cost of treatment which was mostly based on preliminary diagnosis. The greatest quality-of-life (QOL) benefits from patch testing relative to nonpatch testing occurred in patients with recurrent/chronic ACD.

CONCLUSIONS

Patch testing is most cost effective and reduces the cost of therapy in patients with severe ACD. Greater improvements in quality of life were seen in patients with recurrent/chronic ACD who were patch tested than patients who were not patch tested within the same group. Results were not sensitive to changes due to the addition of indirect costs or costs using generic substitution.

The origin of differences in the physical properties of the equilibrium forms of cytochrome b5 revealed through high-resolution NMR structures and backbone dynamic analyses

On the basis of a comparison of high-resolution solution structures calculated for both equilibrium forms of rat ferrocytochrome b5, differences in reduction potential and thermodyanmic stability have been characterized in terms of significant structural and dynamic differences between the two forms. The dominant difference between A and B conformations has long been known to be due to a 180 degrees rotation of the heme in the binding pocket about an axis defined by the alpha- and gamma-meso carbons, however, the B form has not been structurally characterized until now. The most significant differences observed between the two forms were the presence of a hydrogen bond between the 7-propionate and the S64 amide in the A form but not the B form and surprisingly a displacement of the heme out of the binding pocket by 0.9 A in the B form relative to the A form. The magnitude of other factors which could contribute to the known difference in reduction potentials in the bovine protein [Walker, F. A., Emrick, D., Rivera, J. E., Hanquet, B. J., and Buttlaire, D. H. (1988) J. Am. Chem. Soc. 110, 6234-6240], such as differences in the orientation of the axial imidazoles and differences in hydrogen bond strength to the imidazoles, have been evaluated. The dominant effector of the reduction potential would appear to be the lack of the hydrogen bond to the S64 amide in the B form which frees up the propionate to charge stabilize the iron in the oxidized state and thus lower the reduction potential of the B form. The structure we report for the A form, based on heteronuclear NMR restraints, involving a total of 1288 restraints strongly resembles both the X-ray crystal structure of the bovine protein and a recently reported structure for the A form of the rat protein based on homonuclear data alone [Banci, L., Bertini, I., Ferroni, F., and Rosato, A. (1997) Eur. J. Biochem. 249, 270-279]. The rmsd for the backbone atoms of the A form is 0.54 A (0.92 A for all non-hydrogens). The rmsd for the backbone of the B form is 0.51 A (0. 90 A for all non-hydrogen atoms). An analysis of backbone dynamics based on a model-free analysis of 15N relaxation data, which incorporated axially symmetric diffusion tensor modeling of the cytochrome, indicates that the protein is more rigid in the reduced state relative to the oxidized state, based on a comparison with order parameters reported for the bovine protein in the oxidized state [Kelly, G. P., Muskett, F. W., and Whitford, D. (1997) Eur. J. Biochem. 245, 349-354].

Effect of axial ligand plane reorientation on electronic and electrochemical properties observed in the A67V mutant of rat cytochrome b5

Mutational studies directed at evaluating the effect of the axial ligand plane orientation on electrochemical properties of cytochrome b5 have been performed. As described in the previous paper, structural consequences of one of these mutations, the A67V mutation, have been evaluated using NMR solution methods. The lack of large shifts relative to the wild-type protein in both the imidazole Ndelta nitrogen and proton resonances of the H63 imidazole ring indicates that the hydrogen bond between the carbonyl of F58 and the imidazole ring of H63 remains intact in this mutant. Effects of the imidazole plane reorientation on the Fe d-orbitals were evaluated on the basis of interpretation of EPR spectra, near-infrared bands associated with ligand-to-metal charge transfer transitions, reorientation of the anisotropy of the paramagnetic center determined by calculation of pseudocontact shifts, and the temperature dependence of the contact-shifted resonances. The dominant effect of the imidazole reorientation appears to have been a destabilization of the d(xz) orbital energy and a reorientation of the d(pi) orbitals. This is surprising in light of the -20 mV shift in the reduction potential of the mutant relative to the wild-type protein and indicates that a destabilization of d(yz)-orbital energy level of the reduced state dictates the observed change in reduction potential. Measured values for the reorganizational energy and heterogeneous electron transfer rates were indistinguishable for wild-type and mutant proteins. This is perhaps surprising, given significant differences in the pattern of electron delocalization into the porphyrin ring observed as significantly altered contact shift patterns. Mutational studies perturbing the H39 imidazole were also performed but with more limited success.

Characterization of a site-directed mutant of cytochrome b5 designed to alter axial imidazole ligand plane orientation

Mutants of cytochrome b5 were designed to achieve reorientation of individual axial imidazole ligands. The orientation of the axial ligand planes is thought to modulate the reduction potential of bis(imidazole) axially ligated heme proteins. The A67V mutation achieved this goal through the substitution of a bulkier, hydrophobic ligand for a residue, in the sterically hindered hydrophobic heme binding pocket. Solution structures of mutant and wild-type proteins in the region of the mutation were calculated using restraints obtained from 1H and 15N 2D homonuclear and heteronuclear NMR spectra and 1H-15N 3D heteronuclear NMR spectra. More than 10 restraints per residue were used in the refinement of both structures. Average local rmsd for 20 refined structures was 0.30 A for the wild-type structure and 0.38 A for the A67V mutant. The transfer of amide proton resonance assignments from wild-type to the mutant protein was achieved through overlays of 15N-1H heteronuclear correlation spectra of the reduced proteins. Side chain assignments and sequential assignments were established using conventional assignment strategies. Calculation of the orientation of the components of the anisotropic paramagnetic susceptibility tensor, using methods similar to procedures applied to the wild-type protein, shows that the orientation of the in-plane components are identical in the wild-type and mutant proteins. However, the orientation of the z-component of the susceptibility tensor calculated for the mutant protein differs by 17 degrees for the A-form and by 11 degrees for the B-form from the orientation calculated for the wild-type protein. The rotation of the z-component of the susceptibility tensor (toward the delta meso proton) is in the same direction and is of the same magnitude as the rotation of the H63 imidazole ring induced by mutation.

1H, 13C and 15N NMR assignments and secondary structure of the paramagnetic form of rat cytochrome b5

Modern multidimensional double- and triple-resonance NMR methods have been applied to assign the backbone and side-chain 13C resonances for both equilibrium conformers of the paramagnetic form of rat liver microsomal cytochrome b5. The assignment of backbone 13C resonances was used to confirm previous 1H and 15N resonance assignments [Guiles, R.D. et al. (1993) Biochemistry, 32, 8329-8340]. On the basis of short- and medium-range NOEs and backbone 13C chemical shifts, the solution secondary structure of rat cytochrome b5 has been determined. The striking similarity of backbone 13C resonances for both equilibrium forms strongly suggests that the secondary structures of the two isomers are virtually identical. It has been found that the 13C chemical shifts of both backbone and side-chain atoms are relatively insensitive to paramagnetic effects. The reliability of such methods in anisotropic paramagnetic systems, where large pseudocontact shifts can be observed, is evaluated through calculations of the magnitude of such shifts.

Pseudocontact shifts used in the restraint of the solution structures of electron transfer complexes

The geometry of the ferricytochrome b5-ferricytochrome c complex has been analysed using long-range interprotein paramagnetic dipolar shifts. Heteronuclear filtered NMR spectra of samples containing 15N-labelled cytochrome b5 in complex with unlabelled cytochrome c allowed unambiguous assessment of pseudocontact shifts relative to diamagnetic reference states. Because pseudocontact shifts can be observed for protons as much as 20 A from the paramagnetic centre, this approach allows study of electron transfer proteins in fast exchange. Our findings provide the first physical evidence confirming hypotheses presented in previous theoretical studies. This absence of certain predicted shifts that are expected based on the best fit to a static model of the complex suggests that cytochrome b5 is more dynamic in solution than in the crystal, in agreement with molecular dynamics simulations.