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Biomedical subjects

M A Walsh

Publications and source records attributed to M A Walsh.

At least 19 recordsLinked to original sources
PubMed2006

Automation of sample mounting for macromolecular crystallography.

A standard sample holder and vial for cryocooled macromolecular crystals has been defined for use with robotic sample changers. This SPINE standard sample holder is a modified version, with added features and specifications, of sample holders in common use. In particular, the SPINE standard meets the precision required for automatic sample exchange and includes a cap that is identified by a two-dimensional datamatrix code as well as an optional vial. At the ESRF, the sample holder standard is in use with the EMBL/ESRF/BM14 robotic sample changer (SC3) which is installed on eight beamlines. The SC3 can hold up to 50 crystals stored in five baskets. A datamatrix reader in the SC3 ensures safe management of the sample flow and facilitates fully automatic screening and characterization of samples. Tools for handling and transporting 50 samples in a dry shipping dewar have been developed. In addition to the SC3, the SPINE sample holder is currently compatible with a number of other robotic sample changers.

Automation↗
PubMed2006

Atrioventricular block after transcatheter closure of perimembranous ventricular septal defects.

OBJECTIVE: To look at the presentation, treatment and outcome of patients who developed atrioventricular block after transcatheter closure of a perimembranous ventricular septal defect (PMVSD) with the Amplatzer PMVSD device. SETTING: Three tertiary referral centres for paediatric cardiology in two countries. RESULTS: All three patients presented within 10 days of the procedure. All three patients were treated with intravenous steroids. A permanent pacemaker was inserted in all patients but no pacemaker required activation after two months. CONCLUSION: Complete atrioventricular block occurring in the weeks after device occlusion of a PMVSD appears to resolve quickly. Continued involvement in multicentre device databases is required to monitor safety.

Anti-Inflammatory Agents↗
PubMed2006

Impostor cell lines.

Explore the source record for details and available documents.

Carcinoma, Squamous Cell↗
PubMed2006

A comparison of temporal bone fracture classification systems.

OBJECTIVES: To compare the traditional and otic capsule classification system of temporal bone fractures for clinical relevance. DESIGN: A retrospective review of all patients with a radiological diagnosis of a skull-base fracture over a 5-year period. SETTING: All patients were seen at Beaumont Hospital, the national tertiary referral centre for Neuro-otology. PARTICIPANTS: Patients with a clinical diagnosis of skull fracture were identified from the hospitals in patient enquiry (HIPE) database. Of 338 patients, 31 (9%) were identified as having a temporal bone fracture on high-resolution CT scanning. MAIN OUTCOME AND MEASURES: The rate and distribution of each major clinical complications within each classification system to establish if either one was more clinically useful. RESULTS: Fractures were classified as mixed in 14 (45%), longitudinal in 9 (29%) and horizontal in 8 (26%). Alternatively, 2 (7%) were otic capsule violating and 29 (93%) were otic capsule sparing. Seventeen patients (54.8%) sustained a hearing loss. Seven patients (23%) sustained a facial nerve injury. Four (13%) developed a cerebrospinal fluid (CSF) leak. Of all clinical findings only sensorineural hearing loss occurred significantly more often in the horizontal as opposed to the longitudinal group (P = 0.029) and in the otic violating as opposed to the otic sparing group (P = 0.013). CONCLUSIONS: We acknowledge that the relatively small size of our cohort diminishes the statistical power of our conclusions. However, we found that the otic capsule-based classification system was not significantly better than the traditional system in predicting the likelihood of sustaining specific injuries from fractures of the temporal bone.

Brain Injuries↗
PubMed2005

Induction of nasal hyper-responsiveness by allergen challenge in allergic rhinitis: the role of afferent and efferent nerves.

BACKGROUND: Hyper-responsiveness of nasal secretory function and volume changes are features of allergic rhinitis (AR) that are mediated in part by neural mechanisms. The finding of nasal hyper-responsiveness in subjects with AR who are currently symptomatic, but not in those who are currently out of season and asymptomatic, suggests that induction of neural reflexes in allergic subjects occurs as a result of allergic inflammation. OBJECTIVES: To investigate whether allergen exposure in subjects with asymptomatic seasonal allergic rhinitis (SAR) may lead to induction of neural reflexes, and to investigate the components of the reflexes involved in this induction. METHODS: Asymptomatic subjects with (out-of-season) SAR underwent a nasal bradykinin challenge, before and 24 h after preceding ipsilateral (n = 11) and contralateral (n = 11) antigen challenge. Challenges were performed and nasal secretions collected using filter paper disks, and changes in nasal minimal cross-sectional area (A(min)) were measured using acoustic rhinometry. RESULTS: Preceding ipsilateral antigen challenge led to the induction of a contralateral secretory reflex (P = 0.01), which was absent in control experiments (P = 0.34). Ipsilateral secretion weights were also enhanced. Preceding contralateral antigen challenge also induced a contralateral secretory reflex (P = 0.03). Enhancement of the reduction in contralateral A(min) was also seen (P = 0.02). Ipsilateral responses were unchanged. CONCLUSIONS: Allergen exposure in asymptomatic allergic subjects leads to induction of neural reflexes, resulting in nasal hyper-responsiveness, which persists beyond the resolution of the acute allergic response. Our data suggest that the mechanisms of allergen-induced hyper-responsiveness involve both afferent and efferent components.

Adolescent↗
PubMed2004

An alternative technique for nasal biopsy.

OBJECTIVES/HYPOTHESIS: The objective was to investigate the effectiveness of co-phenylcaine as a topical anesthetic agent for nasal mucosal biopsy. STUDY DESIGN: A prospective study. METHODS: Nasal mucosal biopsy specimens were taken from a site just anterior to the inferior turbinate following topical anesthesia with co-phenylcaine. All volunteers graded pain according to standard visual analogue scale (0-10) (VAS) scoring, and all were followed up after 24 hours for any epistaxis. RESULTS: Ninety nasal biopsy specimens were removed from 41 patients in all. Eight-two percent did not report any discomfort following this procedure (VAS score, 0). Ten patients reported mild discomfort (VAS scores ranging between, 1 and 3) and only six reported pain (VAS scores ranging from 5 to 7). However, five of these patients agreed to further biopsy and documented no discomfort during the repeat procedure. Only one patient required immediate intervention for hemorrhage after the procedure. In cases in which bleeding occurred (seven patients) it was documented within the first 6 hours, was minimal in content, and was controlled with local pressure. No systemic side effects were experienced. CONCLUSION: Co-phenylcaine is a suitable topical anesthetic agent for nasal mucosal biopsy. Removal of nasal tissue from a site anterior to the inferior turbinate can be performed under direct vision and provides sufficient tissue for histological assessment.

Adolescent↗
PubMed2002

The potential of virtual laryngoscopy in the assessment of vocal cord lesions.

Virtual laryngoscopy is a useful adjunctive radiological tool in the assessment of laryngeal lesions. A total of 10 patients requiring direct laryngoscopy for the investigation of laryngeal lesions underwent preoperative virtual laryngoscopy using three-dimensional reconstruction of two-dimensional computerized tomography (CT) images. All lesions were correctly diagnosed on virtual laryngoscopy before direct laryngoscopy. Its main advantages are that it does not require general anaesthesia, it allows three-dimensional visualization of the airway beyond areas of narrowing and it gives a highly accurate representation of vocal cord lesions, both in terms of definition and spatial representation. Its disadvantages are that it does not provide histology, it requires an air-mucosa interface to produce an image and it cannot identify functional lesions of the vocal cords.

Adult↗
PubMed2002

Somatostatin therapy for glomus tumors: a report of two cases.

Glomus tumors of the head and neck are benign vascular lesions that often provide dilemmas in management. The presence of somatostatin receptors on the tumor cell surface has facilitated an additional imaging technique in the form of radiolabeled octreotide scanning. The use of the somatostatin analogue, octreotide, also provides a therapeutic option for inoperable or recurrent tumors. We present two patients, one with a surgically inaccessible tumor that recurred after primary radiotherapy and one who underwent incomplete resection because of the tumor's proximity to the internal carotid artery. Neither tumor has shown further growth 5 and 3 years after treatment with octreotide, respectively.

Case Reports↗
PubMed2001

Crystal structures of penicillin acylase enzyme-substrate complexes: structural insights into the catalytic mechanism.

The crystal structure of penicillin G acylase from Escherichia coli has been determined to a resolution of 1.3 A from a crystal form grown in the presence of ethylene glycol. To study aspects of the substrate specificity and catalytic mechanism of this key biotechnological enzyme, mutants were made to generate inactive protein useful for producing enzyme-substrate complexes. Owing to the intimate association of enzyme activity and precursor processing in this protein family (the Ntn hydrolases), most attempts to alter active-site residues lead to processing defects. Mutation of the invariant residue Arg B263 results in the accumulation of a protein precursor form. However, the mutation of Asn B241, a residue implicated in stabilisation of the tetrahedral intermediate during catalysis, inactivates the enzyme but does not prevent autocatalytic processing or the ability to bind substrates. The crystal structure of the Asn B241 Ala oxyanion hole mutant enzyme has been determined in its native form and in complex with penicillin G and penicillin G sulphoxide. We show that Asn B241 has an important role in maintaining the active site geometry and in productive substrate binding, hence the structure of the mutant protein is a poor model for the Michaelis complex. For this reason, we subsequently solved the structure of the wild-type protein in complex with the slowly processed substrate penicillin G sulphoxide. Analysis of this structure suggests that the reaction mechanism proceeds via direct nucleophilic attack of Ser B1 on the scissile amide and not as previously proposed via a tightly H-bonded water molecule acting as a "virtual" base.

Amino Acid Substitution↗
PubMed2001

A thermophilic mini-chaperonin contains a conserved polypeptide-binding surface: combined crystallographic and NMR studies of the GroEL apical domain with implications for substrate interactions.

A homologue of the Escherichia coli GroEL apical domain was obtained from thermophilic eubacterium Thermus thermophilus. The domains share 70 % sequence identity (101 out of 145 residues). The thermal stability of the T. thermophilus apical domain (Tm>100 degrees C as evaluated by circular dichroism) is at least 35 degrees C greater than that of the E. coli apical domain (Tm=65 degrees C). The crystal structure of a selenomethione-substituted apical domain from T. thermophilus was determined to a resolution of 1.78 A using multiwavelength-anomalous-diffraction phasing. The structure is similar to that of the E. coli apical domain (root-mean-square deviation 0.45 A based on main-chain atoms). The thermophilic structure contains seven additional salt bridges of which four contain charge-stabilized hydrogen bonds. Only one of the additional salt bridges would face the "Anfinsen cage" in GroEL. High temperatures were exploited to map sites of interactions between the apical domain and molten globules. NMR footprints of apical domain-protein complexes were obtained at elevated temperature using 15N-1H correlation spectra of 15N-labeled apical domain. Footprints employing two polypeptides unrelated in sequence or structure (an insulin monomer and the SRY high-mobility-group box, each partially unfolded at 50 degrees C) are essentially the same and consistent with the peptide-binding surface previously defined in E. coli GroEL and its apical domain-peptide complexes. An additional part of this surface comprising a short N-terminal alpha-helix is observed. The extended footprint rationalizes mutagenesis studies of intact GroEL in which point mutations affecting substrate binding were found outside the "classical" peptide-binding site. Our results demonstrate structural conservation of the apical domain among GroEL homologues and conservation of an extended non-polar surface recognizing diverse polypeptides.

Amino Acid Sequence↗
PubMed2001

Relationship between intracoronary and peripheral expression of soluble cell adhesion molecules.

BACKGROUND: Elevated levels of soluble cell adhesion molecules (sCAMs) have been reported in various coronary artery disease processes. The principle stimulus for expression of sCAMs is believed to be an inflamed atherosclerotic plaque within the coronary vessel. The relationship between levels of sCAMs in the coronary circulation and the peripheral circulation has not been defined. The primary aim of this study was to define the relationship between levels of sCAMs sampled from the systemic circulation and from the coronary circulation. We also set out to document the acute expression of soluble CAMs following coronary angioplasty with or without stent implantation. METHODS: The coronary sinus was cannulated in patients undergoing LAD angioplasty. Samples were drawn from left coronary ostium (LCO) and coronary sinus (CS) and femoral vein simultaneously before, immediately after and 4 h after the PTCA procedure. Levels of sICAM-1, sVCAM-1, sE-selectin and sP-selectin were measured using ELISA technique. RESULTS: 10 patients (7 male/3 female, 61+/-11 y) entered the study. There was no significant difference in the levels of sICAM-1, sVCAM-1, sE-selectin and sPselectin whether sampled from left coronary ostium, coronary sinus or femoral vein at all time points. There was no significant change in the acute expression of sICAM-1, sVCAM-1 and sE-selectin following coronary angioplasty. Levels of sP-selectin fell significantly during the PTCA procedure (142+/-7 ng/ml to 64+/-6 ng/ml, P<0.001) but then rose again after 4 h and returned toward baseline levels at 24 h. CONCLUSION: Levels of soluble CAMs sampled in the systemic circulation directly reflect levels in the coronary circulation. Coronary angioplasty results in rapid fall in levels of sP-selectin which returns to normal within 24 h following the procedure.

Aged↗
PubMed2001

Intracranial complications of acute frontal sinusitis.

Despite advances in the diagnosis and treatment of acute frontal sinusitis, there is still significant occurrence of intracranial complications. Urgent surgical evacuation of any intracranial collection is required; however, the surgical management of the associated sinusitis remains controversial. Ten patients presented to this department over a 12-month period with subdural empyema secondary to acute frontal sinusitis. Four patients had a coexisting Pott's puffy tumour and one patient had a periorbital abscess. Each patient was managed using a multidisciplinary approach. A frontal sinus trephine/drain +/- antral washout was performed at the same time as craniotomy with evacuation of the empyema. With this approach only two patients suffered long-term morbidity in our series, in the form of persistent neurological or cognitive deficit. No patient required a definitive sinus procedure. This study emphasizes the need for the early assessment and intervention of patients with an intracranial complication secondary to acute frontal sinusitis. Further assessment of the underlying sinus disease is indicated during outpatient follow up after the acute episode.

Acute Disease↗
PubMed2000

Structure of RsrI methyltransferase, a member of the N6-adenine beta class of DNA methyltransferases.

DNA methylation is important in cellular, developmental and disease processes, as well as in bacterial restriction-modification systems. Methylation of DNA at the amino groups of cytosine and adenine is a common mode of protection against restriction endonucleases afforded by the bacterial methyltransferases. The first structure of an N:6-adenine methyltransferase belonging to the beta class of bacterial methyltransferases is described here. The structure of M. RSR:I from Rhodobacter sphaeroides, which methylates the second adenine of the GAATTC sequence, was determined to 1.75 A resolution using X-ray crystallography. Like other methyltransferases, the enzyme contains the methylase fold and has well-defined substrate binding pockets. The catalytic core most closely resembles the PVU:II methyltransferase, a cytosine amino methyltransferase of the same beta group. The larger nucleotide binding pocket observed in M. RSR:I is expected because it methylates adenine. However, the most striking difference between the RSR:I methyltransferase and the other bacterial enzymes is the structure of the putative DNA target recognition domain, which is formed in part by two helices on an extended arm of the protein on the face of the enzyme opposite the active site. This observation suggests that a dramatic conformational change or oligomerization may take place during DNA binding and methylation.

Adenine↗
PubMed2000

Structure of cyanase reveals that a novel dimeric and decameric arrangement of subunits is required for formation of the enzyme active site.

BACKGROUND: Cyanase is an enzyme found in bacteria and plants that catalyzes the reaction of cyanate with bicarbonate to produce ammonia and carbon dioxide. In Escherichia coli, cyanase is induced from the cyn operon in response to extracellular cyanate. The enzyme is functionally active as a homodecamer of 17 kDa subunits, and displays half-site binding of substrates or substrate analogs. The enzyme shows no significant amino acid sequence homology with other proteins. RESULTS: We have determined the crystal structure of cyanase at 1.65 A resolution using the multiwavelength anomalous diffraction (MAD) method. Cyanase crystals are triclinic and contain one homodecamer in the asymmetric unit. Selenomethionine-labeled protein offers 40 selenium atoms for use in phasing. Structures of cyanase with bound chloride or oxalate anions, inhibitors of the enzyme, allowed identification of the active site. CONCLUSIONS: The cyanase monomer is composed of two domains. The N-terminal domain shows structural similarity to the DNA-binding alpha-helix bundle motif. The C-terminal domain has an 'open fold' with no structural homology to other proteins. The subunits of cyanase are arranged in a novel manner both at the dimer and decamer level. The dimer structure reveals the C-terminal domains to be intertwined, and the decamer is formed by a pentamer of these dimers. The active site of the enzyme is located between dimers and is comprised of residues from four adjacent subunits of the homodecamer. The structural data allow a conceivable reaction mechanism to be proposed.

Binding Sites↗
PubMed2000

Inhibition of the hepatitis C virus NS3/4A protease. The crystal structures of two protease-inhibitor complexes.

The hepatitis C virus NS3 protein contains a serine protease domain with a chymotrypsin-like fold, which is a target for development of therapeutics. We report the crystal structures of this domain complexed with NS4A cofactor and with two potent, reversible covalent inhibitors spanning the P1-P4 residues. Both inhibitors bind in an extended backbone conformation, forming an anti-parallel beta-sheet with one enzyme beta-strand. The P1 residue contributes most to the binding energy, whereas P2-P4 side chains are partially solvent exposed. The structures do not show notable rearrangements of the active site upon inhibitor binding. These results are significant for the development of antivirals.

Amino Acid Sequence↗
PubMed2000

Nitinol stents: their value in tracheobronchial obstruction.

Recurrent tracheobronchial obstruction whether due to a benign or malignant cause is not always amenable to surgery and one is left with the dilemma of what to do for a patient who is slowly asphyxiating. Various modalities have been employed in the past with varying degrees of success. However due to the recent innovations in 'superelastic' biocompatible alloys we present our clinical experience with a new generation of metallic stents made from Nitinol. Over a 12-month period we inserted eight stents in six patients with malignant and benign tracheobronchial obstruction. Almost all patients had dramatic improvement in their symptoms and there was little airway reaction observed up to 18 months after insertion. However, one should exercise caution in inserting them for benign conditions as we regard them as permanent implants. Also evident is the inherent morbidity in this group of patients and this needs to be carefully considered prior to treatment.

Adult↗