Staged surgical management of the sequelae of neonatal septic hip arthritis: a case report and review of the literature.

Total necrosis of the femoral head is a common sequelae after septic hip arthritis in infancy. Septic hip dislocation may develop, with severe functional consequences on the growing child: limping and limb length discrepancy. We present our staged surgical treatment of Choi's type IV A sequelae of septic hip arthritis in a 2-year old boy. Open reduction, followed by various reconstructive procedures, were performed. After 8 years of follow-up, the child has a stable, mobile hip, with good functional outcomes. Close follow-up is mandatory to ensure a good long-term outcome. Our technique proved to be successful in the achievement of a functional hip by maintaining the remnants of the femoral head and creating the conditions to remodel them quasi-normal.

Descriptive epidemiology of clubfoot in Romania: a clinic-based study.

OBJECTIVE: Congenital clubfoot affects 1 per 1000 live births per year in Romania. To date, no epidemiological studies have been conducted in this country to assess risk factors associated with the deformity. The aim of this study was to evaluate specific environmental and socio-demographic factors that may increase the risk of an infant to be born with clubfoot. PATIENTS AND METHODS: A descriptive clinic-based study over a twelve-week period was conducted using structured questionnaires given to biological parents of clinically confirmed clubfoot and control subjects. 62 parents of probands and 66 parents of control patients were enrolled for risk factor questionnaires. Phenotypic data from clubfoot children was also collected. RESULTS: We found that males were twice as likely to have clubfoot and half of clubfoot subjects were affected bilaterally. There was no significant difference in the rate of left versus right clubfoot. Infant and maternal characteristics showing a strong association with clubfoot included breech presentation and old maternal age at conception. CONCLUSIONS: Our results support reported literature data that males are two times as likely to have clubfoot which indicates a genetic influence. Previous reports suggest clubfoot babies are born to young mothers but in Romania advanced maternal age (≥ 35 years) was an indicator which may suggest genetic influence. This clinic-based study does not support previously recorded data of a positive association for maternal or household smoking. Data from this Romanian population also does not support previous data suggesting strong associations with maternal diabetes.

The endoplasmic reticulum-based acetyltransferases, ATase1 and ATase2, associate with the oligosaccharyltransferase to acetylate correctly folded polypeptides.

The endoplasmic reticulum (ER) has two membrane-bound acetyltransferases responsible for the endoluminal N(ϵ)-lysine acetylation of ER-transiting and -resident proteins. Mutations that impair the ER-based acetylation machinery are associated with developmental defects and a familial form of spastic paraplegia. Deficient ER acetylation in the mouse leads to defects of the immune and nervous system. Here, we report that both ATase1 and ATase2 form homo- and heterodimers and associate with members of the oligosaccharyltransferase (OST) complex. In contrast to the OST, the ATases only modify correctly folded polypetides. Collectively, our studies suggest that one of the functions of the ATases is to work in concert with the OST and "select" correctly folded from unfolded/misfolded transiting polypeptides.

Site-directed spin labeling reveals pentameric ligand-gated ion channel gating motions.

Pentameric ligand-gated ion channels (pLGICs) are neurotransmitter-activated receptors that mediate fast synaptic transmission. In pLGICs, binding of agonist to the extracellular domain triggers a structural rearrangement that leads to the opening of an ion-conducting pore in the transmembrane domain and, in the continued presence of neurotransmitter, the channels desensitize (close). The flexible loops in each subunit that connect the extracellular binding domain (loops 2, 7, and 9) to the transmembrane channel domain (M2-M3 loop) are essential for coupling ligand binding to channel gating. Comparing the crystal structures of two bacterial pLGIC homologues, ELIC and the proton-activated GLIC, suggests channel gating is associated with rearrangements in these loops, but whether these motions accurately predict the motions in functional lipid-embedded pLGICs is unknown. Here, using site-directed spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy and functional GLIC channels reconstituted into liposomes, we examined if, and how far, the loops at the ECD/TMD gating interface move during proton-dependent gating transitions from the resting to desensitized state. Loop 9 moves ∼9 Šinward toward the channel lumen in response to proton-induced desensitization. Loop 9 motions were not observed when GLIC was in detergent micelles, suggesting detergent solubilization traps the protein in a nonactivatable state and lipids are required for functional gating transitions. Proton-induced desensitization immobilizes loop 2 with little change in position. Proton-induced motion of the M2-M3 loop was not observed, suggesting its conformation is nearly identical in closed and desensitized states. Our experimentally derived distance measurements of spin-labeled GLIC suggest ELIC is not a good model for the functional resting state of GLIC, and that the crystal structure of GLIC does not correspond to a desensitized state. These findings advance our understanding of the molecular mechanisms underlying pLGIC gating.

Ligand-binding domain of an α7-nicotinic receptor chimera and its complex with agonist.

The α(7) acetylcholine receptor (AChR) mediates pre- and postsynaptic neurotransmission in the central nervous system and is a potential therapeutic target in neurodegenerative, neuropsychiatric and inflammatory disorders. We determined the crystal structure of the extracellular domain of a receptor chimera constructed from the human α(7) AChR and Lymnaea stagnalis acetylcholine binding protein (AChBP), which shares 64% sequence identity and 71% similarity with native α(7). We also determined the structure with bound epibatidine, a potent AChR agonist. Comparison of the structures revealed molecular rearrangements and interactions that mediate agonist recognition and early steps in signal transduction in α(7) AChRs. The structures further revealed a ring of negative charge within the central vestibule, poised to contribute to cation selectivity. Structure-guided mutational studies disclosed distinctive contributions to agonist recognition and signal transduction in α(7) AChRs. The structures provide a realistic template for structure-aided drug design and for defining structure-function relationships of α(7) AChRs.

Packing of the extracellular domain hydrophobic core has evolved to facilitate pentameric ligand-gated ion channel function.

Protein function depends on conformational flexibility and folding stability. Loose packing of hydrophobic cores is not infrequent in proteins, as the enhanced flexibility likely contributes to their biological function. Here, using experimental and computational approaches, we show that eukaryotic pentameric ligand-gated ion channels are characterized by loose packing of their extracellular domain ß-sandwich cores, and that loose packing contributes to their ability to rapidly switch from closed to open channel states in the presence of ligand. Functional analyses of GABA(A) receptors show that increasing the ß-core packing disrupted GABA-mediated currents, with impaired GABA efficacy and slowed GABA current activation and desensitization. We propose that loose packing of the hydrophobic ß-core developed as an evolutionary strategy aimed to facilitate the allosteric mechanisms of eukaryotic pentameric ligand-gated ion channels.

Crystal structure of the extracellular domain of nAChR alpha1 bound to alpha-bungarotoxin at 1.94 A resolution.

We determined the crystal structure of the extracellular domain of the mouse nicotinic acetylcholine receptor (nAChR) alpha1 subunit bound to alpha-bungarotoxin at 1.94 A resolution. This structure is the first atomic-resolution view of a nAChR subunit extracellular domain, revealing receptor-specific features such as the main immunogenic region (MIR), the signature Cys-loop and the N-linked carbohydrate chain. The toxin binds to the receptor through extensive protein-protein and protein-sugar interactions. To our surprise, the structure showed a well-ordered water molecule and two hydrophilic residues deep in the core of the alpha1 subunit. The two hydrophilic core residues are highly conserved in nAChRs, but correspond to hydrophobic residues in the nonchannel homolog acetylcholine-binding proteins. We carried out site-directed mutagenesis and electrophysiology analyses to assess the functional role of the glycosylation and the hydrophilic core residues. Our structural and functional studies show essential features of the nAChR and provide new insights into the gating mechanism.

Structural determinants for alpha-neurotoxin sensitivity in muscle nAChR and their implications for the gating mechanism.

Neurotoxins from snake venoms act as potent antagonists on the nicotinic acetylcholine receptors (nAChRs). Alpha-neurotoxins such as alpha-bungarotoxin (alpha-Btx) selectively bind to the skeletal muscle nAChRs among other subtypes, causing failure of the neuromuscular transmission. Through evolution, some species including snakes and mongoose have developed resistance to alpha-neurotoxins via specific amino acid substitutions in their muscle-type nAChR alpha1 subunit, which constitutes most of the toxin-binding site. Here we analyze these sequence variations in the context of our recent crystal structure of the extracellular domain of the mouse nAChR alpha1 bound to alpha-Btx. Our structure suggests that alpha-Btx has evolved as an extremely potent antagonist of muscle nAChR by binding the receptor tightly, blocking its ligand site, and locking its conformation in a closed state. Conversely, most toxin-resistant mutations occur at the alpha-Btx binding interface on nAChR alpha1 but away from the agonist binding site. These mutations can interfere with the binding of alpha-Btx without having deleterious effect on the gating function. These analyses not only help understand the structural determinants for neurotoxin sensitivity in muscle-type nAChR, but also shed light on its gating mechanism.

Quaternary structure of alpha-crustacyanin from lobster as seen by small-angle X-ray scattering.

The structure of alpha-crustacyanin, the blue carotenoprotein of lobster (Homarus gammarus) carapace, has been investigated for the first time using small-angle X-ray scattering. In this paper, we have determined the dimensions of this protein composed of eight heterodimeric subunits of beta-crustacyanin. Analysis of the scattering spectra and estimation of the shape of alpha-crustacyanin show that the protein fits into a cylinder with an axial length of 238 A and a radius of 47.5 A, in which the eight beta-crustacyanin molecules are probably arranged in a helical manner.

Conservative treatment of cervico-facial suppurations.

The author prefers conservative treatment of suppurations in the cervico-facial area. It consists of evacuation of pus by puncture and simultaneous instillation of antibiotics. The technique for superficial and deep infections is described. On the basis of 470 cases treated the method is considered very efficient.