Crystallization and preliminary crystallographic studies of a ribosomal protein L30e from the hyperthermophilic archaeonThermococcus celer

Ribosomal protein L30e from the hyperthermophilic archaeon Thermococcus celer is a good model for the study of the thermostability of proteins. It has been overexpressed, purified and crystallized using the hanging-drop vapour-diffusion method using PEG 8000 as precipitant at 290 K. The crystal belongs to the hexagonal space group P6(1)/P6(5), with unit-cell parameters a = b = 48.32, c = 86.42 A. The asymmetric unit contains a single molecule of L30e, with a corresponding crystal volume per protein mass (V(M)) of 2.68 A(3) Da(-1) and a solvent content of 54%. A complete data set diffracting to 1.96 A resolution was collected from a single crystal at 100 K.

Long-term outcome for patients with split cord malformation

Object

Split cord malformations (SCMs) are relatively rare forms of occult spinal dysraphism (OSD) and tethered spinal cord syndrome. The majority of these cases present in early childhood, with neurocutaneous stigmata being an early presenting feature. Prophylactic detethering surgery is advocated by most neurosurgeons due to the risk of neurological deterioration over time caused by patient growth and activity. However, unlike other forms of OSD, the course of SCM progression after surgery is not well understood, and little has been published about long-term follow-up results. In this study the authors review the results obtained in 16 patients in whom the senior author performed surgery over a 13-year period (average length of follow up almost 8 years).

Methods

Presentation, surgical approach, and outcome are evaluated, and the long-term outcome of neurological status, pain, bowel/bladder disturbance, and spinal deformities are emphasized.

Conclusions

The primary conclusion is that patients with SCM generally tolerate surgery well and experience few complications. Neurological deterioration is rare except in cases in which retethering occurs, (two patients in this series). Although impaired bowel and bladder function was stabilized or improved and pain was reliably relieved postoperatively, preexisting vertebral column deformities usually progressed after surgery and, in most cases, required spinal fusion.

Head and neck injuries in young athletes

Careful study of the pathophysiology and epidemiology of sports-related spine injuries brings to light many common features. The incidence increases as the sport becomes increasingly violent and aggressive. Poor conditioning and lack of knowledge of the proper techniques of the sport put the athlete at significant risk for head and spine injury. Improper helmet fit and the use of the head as an offensive weapon also are common features of injury. Although recognition of these features has resulted in a dramatic reduction in catastrophic neurological injury, the athlete remains at risk for less severe head and spine injury, and concussion remains at epidemic proportions at high school, university, and professional levels. It is hoped that careful recognition of the signs of concussion and knowledge of return-to-play criteria will prevent catastrophic complications from minor head injuries, although the long-term effects of multiple concussions on cognition may be problematic.

Prominent basal emissary foramina in syndromic craniosynostosis: correlation with phenotypic and molecular diagnoses

BACKGROUND AND PURPOSE

Jugular foraminal stenosis (JFS) or atresia (JFA) with collateral emissary veins (EV) has been documented in syndromic craniosynostosis. Disruption of EV during surgery can produce massive hemorrhage. Our purpose was to describe the prevalence of prominent basal emissary foramina (EF), which transmit enlarged EV, in syndromic craniosynostosis. Our findings were correlated with phenotypic and molecular diagnoses.

METHODS

We reviewed the medical records and imaging examinations of 33 patients with syndromic craniosynostosis and known fibroblast growth factor receptor (FGFR) mutations. All patients underwent CT and 14 MR imaging. The cranial base was assessed for size of occipitomastoid EF and jugular foramina (JF). Vascular imaging studies were available from 12 patients. A control group (n = 76) was used to establish normal size criteria for JF and EF.

RESULTS

Phenotypic classification included Crouzon syndrome (n = 10), crouzonoid features with acanthosis nigricans (n = 3), Apert syndrome (n = 10), Pfeiffer syndrome (n = 4), and clinically unclassifiable bilateral coronal synostosis (n = 6). EF > or = 3 mm in diameter and JFS or JFA were identified in 23 patients with various molecular diagnoses. Vascular imaging in patients with JFS or JFA and enlarged EF revealed atresia or stenosis of the jugular veins and enlarged basal EV. JFA was seen in all patients with the FGFR3 mutation with crouzonoid features and acanthosis nigricans. Four patients had prominent EF without JFS. Six patients had normal JF and lacked enlarged EF.

CONCLUSION

Enlarged basal EF are common in syndromic craniosynostosis and are usually associated with JFS or JFA. Bilateral basilar venous atresia is most common in patients with the FGFR3 ala391glu mutation and crouzonoid features with acanthosis nigricans, but may be found in patients with FGFR2 mutations. Skull base vascular imaging should be obtained in patients with syndromic craniosynostosis with enlarged EF.

Crystallization and preliminary crystallographic studies of a SAM domain at the C-terminus of human p73alpha

p73 is a recently discovered homologue of the tumour suppressor p53 and contains all three functional domains of p53. The alpha-splice variant of p73 (p73alpha) contains an additional structural domain near its C--terminus that has sequence homology with the sterile alpha-motif (SAM) domain. This domain is considered to be responsible for mediating protein-protein interactions. Pyramidal crystals of human p73alpha SAM domain were obtained by the hanging-drop vapour-diffusion method with ammonium dihydrogen orthophosphate as the precipitant. The crystals diffract to 2.54 A resolution and belong to the tetragonal space group P4(1)2(1)2, with unit-cell parameters a = b = 32.02, c = 133.84 A. The structure was solved by molecular replacement using the NMR structure of the same protein as the search model.

RNA recognition by a Staufen double-stranded RNA-binding domain

The double-stranded RNA-binding domain (dsRBD) is a common RNA-binding motif found in many proteins involved in RNA maturation and localization. To determine how this domain recognizes RNA, we have studied the third dsRBD from Drosophila Staufen. The domain binds optimally to RNA stem-loops containing 12 uninterrupted base pairs, and we have identified the amino acids required for this interaction. By mutating these residues in a staufen transgene, we show that the RNA-binding activity of dsRBD3 is required in vivo for Staufen-dependent localization of bicoid and oskar mRNAs. Using high-resolution NMR, we have determined the structure of the complex between dsRBD3 and an RNA stem-loop. The dsRBD recognizes the shape of A-form dsRNA through interactions between conserved residues within loop 2 and the minor groove, and between loop 4 and the phosphodiester backbone across the adjacent major groove. In addition, helix alpha1 interacts with the single-stranded loop that caps the RNA helix. Interactions between helix alpha1 and single-stranded RNA may be important determinants of the specificity of dsRBD proteins.

The effect of surgery for split spinal cord malformation on neurologic and urologic function

The split spinal cord malformation (SSCM) is an occult spinal dysraphism which causes tethering of the spinal cord. We performed a retrospective analysis of 15 patients who had split cord malformations (without associated open neural tube defect) who underwent both pre- and postoperative urodynamic studies (UDS) in order to determine if a significant percentage of these patients, even in the absence of overt urologic symptoms, had evidence of urologic dysfunction. Eleven patients presenting in early childhood and 4 patients presenting later in life are reviewed. Despite the lack of preoperative urologic symptoms in almost all patients, 73% of patients had voiding abnormalities on formal testing. UDS on these patients before and after surgery was a useful adjunct to perioperative management and decision making, helped define the success of surgery, and gave objective information for cases in which retethering was suspected.

The structure of a tunicate C-type lectin from Polyandrocarpa misakiensis complexed with D -galactose

C-type lectins are calcium-dependent carbohydrate-recognising proteins. Isothermal titration calorimetry of the C-type Polyandrocarpa lectin (TC14) from the tunicate Polyandrocarpa misakiensis revealed the presence of a single calcium atom per monomer with a dissociation constant of 2.6 microM, and confirmed the specificity of TC14 for D -galactose and related monosaccharides. We have determined the 2.2 A X-ray crystal structure of Polyandrocarpa lectin complexed with D -galactose. Analytical ultracentrifugation revealed that TC14 behaves as a dimer in solution. This is reflected by the presence of two molecules in the asymmetric unit with the dimeric interface formed by antiparallel pairing of the two N-terminal beta-strands and hydrophobic interactions. TC14 adopts a typical C-type lectin fold with differences in structure from other C-type lectins mainly in the diverse loop regions and in the second alpha-helix, which is involved in the formation of the dimeric interface. The D -galactose is bound through coordination of the 3 and 4-hydroxyl oxygen atoms with a bound calcium atom. Additional hydrogen bonds are formed directly between serine, aspartate and glutamate side-chains of the protein and the sugar 3 and 4-hydroxyl groups. Comparison of the galactose binding by TC14 with the mannose binding by rat mannose-binding protein reveals how monosaccharide specificity is achieved in this lectin. A tryptophan side-chain close to the binding site and the distribution of hydrogen-bond acceptors and donors around the 3 and 4-hydroxyl groups of the sugar are essential determinants of specificity. These elements are, however, arranged in a very different way than in an engineered galactose-specific mutant of MBPA. Possible biological functions can more easily be understood from the fact that TC14 is a dimer under physiological conditions.

Hot-spot mutants of p53 core domain evince characteristic local structural changes

Most of the oncogenic mutations in the tumor suppressor p53 map to its DNA-binding (core) domain. It is thus a potential target in cancer therapy for rescue by drugs. To begin to understand how mutation inactivates p53 and hence to provide a structural basis for drug design, we have compared structures of wild-type and mutant p53 core domains in solution by NMR spectroscopy. Structural changes introduced by five hot-spot mutations (V143A, G245S, R248Q, R249S, and R273H) were monitored by chemical-shift changes. Only localized changes are observed for G245S, R248Q, R249S, and R273H, suggesting that the overall tertiary folds of these mutant proteins are similar to that of wild type. Structural changes in R273H are found mainly in the loop-sheet-helix motif and the loop L3 of the core domain. Mutations in L3 (G245S, R248Q, and R249S) introduce structural changes in the loop L2 and L3 as well as terminal residues of strands 4, 9, and 10. It is noteworthy that R248Q, which is often regarded as a contact mutant that affects only interactions with DNA, introduces structural changes as extensive as the other loop L3 mutations (G245S and R249S). These changes suggest that R248Q is also a structural mutant that perturbs the structure of loop L2-L3 regions of the p53 core domain. In contrast to other mutants, replacement of the core residue valine 143 to alanine causes chemical-shift changes in almost all residues in the beta-sandwich and the DNA-binding surface. Long-range effects of V143A mutation may affect the specificity of DNA binding.

Spontaneous thrombosis of vein of Galen aneurysmal malformation

Two cases of aneurysmal malformations of the vein of Galen (AVG) with spontaneous thrombosis are reported. Angiogram and MRI before thrombosis demonstrated AVGs with slow arteriovenous shunts and associated stagnation of contrast in the venous sac secondary to severe outflow restriction. Based on these findings, one patient was managed conservatively, and the other underwent placement of a ventriculoperitoneal shunt. Surveillance of the lesions with subsequent MRIs revealed spontaneous thrombosis of the AVGs with excellent clinical outcomes. Proposed mechanisms of spontaneous thrombosis include slow flow shunts, obstruction of the venous outflow or obstruction of the feeding artery. Similar cases in the literature are reviewed with special emphasis on diagnostic tests, symptomatology, mechanisms of thrombosis and therapeutic options.

Thermodynamic stability of wild-type and mutant p53 core domain

Some 50% of human cancers are associated with mutations in the core domain of the tumor suppressor p53. Many mutations are thought just to destabilize the protein. To assess this and the possibility of rescue, we have set up a system to analyze the stability of the core domain and its mutants. The use of differential scanning calorimetry or spectroscopy to measure its melting temperature leads to irreversible denaturation and aggregation and so is useful as only a qualitative guide to stability. There are excellent two-state denaturation curves on the addition of urea that may be analyzed quantitatively. One Zn2+ ion remains tightly bound in the holo-form of p53 throughout the denaturation curve. The stability of wild type is 6.0 kcal (1 kcal = 4.18 kJ)/mol at 25 degrees C and 9.8 kcal/mol at 10 degrees C. The oncogenic mutants R175H, C242S, R248Q, R249S, and R273H are destabilized by 3.0, 2.9, 1.9, 1.9, and 0.4 kcal/mol, respectively. Under certain denaturing conditions, the wild-type domain forms an aggregate that is relatively highly fluorescent at 340 nm on excitation at 280 nm. The destabilized mutants give this fluorescence under milder denaturation conditions.

The role of nitric oxide in focally-evoked limbic seizures

The deep rostral piriform cortex contains a site (area tempestas) in which focal application of picomole amounts of bicuculline, a GABA antagonist, triggers limbic motor seizures which are dependent upon activation of both N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyloxole-4-proprionate subtypes of glutamate receptors. In the present study we determined whether nitric oxide can influence the local modulation of seizure initiation by bicuculline. Nitric oxide and the nitric oxide precursor L-arginine, alone or in combination with low doses of bicuculline were focally administered into the area tempestas of rats. While nitric oxide alone had no significant convulsant effect, L-arginine alone (30-240 nmol) induced brief myoclonic episodes. Nitric oxide (0.7 nmol) and L-arginine (30 nmol) markedly potentiated the seizures evoked by a low dose of bicuculline. The effect of L-arginine was prevented by focal pretreatment with an inhibitor of nitric oxide synthesis, N-nitro-L-arginine methyl ester. However, N-nitro-L-arginine methyl ester did not attenuate the convulsant effect of bicuculline or kainate alone when focally administered into area tempestas. The data demonstrate that exogenously applied nitric oxide or its precursors can enhance seizure triggering activity. However, the data also indicate that L-arginine-nitric oxide pathway does not normally contribute to seizure expression from area tempestas, as N-nitro-L-arginine methyl ester alone did not attenuate focally-evoked seizures.

Focal intracerebral elevation of L-lactate is anticonvulsant

Sodium lactate (pH 7.0) infused over the area tempestas, an epileptogenic site in the prepiriform cortex, protected rats from limbic motor seizures induced by infusion of a GABA receptor antagonist in area tempestas. The anticonvulsant action, which was anatomically site-specific and reversible, persisted for 90 min. Infusions of sodium acetate (pH 5.5 or 7.0) over area tempestas were not anticonvulsant. Our findings suggest that lactate can modulate neural activity and that increased cerebral lactate as occurs with epileptic seizures, may limit the duration and spread of seizure activity.