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Biomedical subjects

Jeffrey Lawton

Publications and source records attributed to Jeffrey Lawton.

3 recordsLinked to original sources

Radial longitudinal deficiency.

Radial longitudinal deficiency encompasses a spectrum of upper limb dysplasias and hypoplasias. The bony abnormalities of the thumb and radius are the most pronounced, but deficiencies of the accompanying muscles, nerves, vessels, and joints also greatly influence the ultimate upper extremity function. The striking clinical presentation of the involved upper limb is often more obvious than the potentially life-threatening associated systemic conditions. All children presenting with radial longitudinal deficiency, regardless of severity, require a renal ultrasound, echocardiogram, and complete blood count to evaluate the potential for associated systemic conditions; these include Fanconi's anemia, the Holt-Oram syndrome, and the VATER (vertebral anomalies, anal atresia, tracheoesophageal fistula, esophageal atresia, renal agenesis) syndrome or VACTERL (vertebral anomalies, anal atresia, cardiac abnormalities, tracheoesophageal fistula, renal agenesis, and limb defects) association. The overall health of the child, as well as the severity of the osseous and soft-tissue deformities of the affected limb, guides the long-term treatment plans.

Abnormalities, Multiple↗

The cathepsin B of Toxoplasma gondii, toxopain-1, is critical for parasite invasion and rhoptry protein processing.

Cysteine proteinases play a major role in invasion and intracellular survival of a number of pathogenic parasites. We cloned a single copy gene, tgcp1, from Toxoplasma gondii and refolded recombinant enzyme to yield active proteinase. Substrate specificity of the enzyme and homology modeling identified the proteinase as a cathepsin B. Specific cysteine proteinase inhibitors interrupted invasion by tachyzoites. The T. gondii cathepsin B localized to rhoptries, secretory organelles required for parasite invasion into cells. Processing of the pro-rhoptry protein 2 to mature rhoptry proteins was delayed by incubation of extracellular parasites with a cathepsin B inhibitor prior to pulse-chase immunoprecipitation. Delivery of cathepsin B to mature rhoptries was impaired in organisms with disruptions in rhoptry formation by expression of a dominant negative micro1-adaptin. Similar disruption of rhoptry formation was observed when infected fibroblasts were treated with a specific inhibitor of cathepsin B, generating small and poorly developed rhoptries. This first evidence for localization of a cysteine proteinase to the unusual rhoptry secretory organelle of an apicomplexan parasite suggests that the rhoptries may be a prototype of a lysosome-related organelle and provides a critical link between cysteine proteinases and parasite invasion for this class of organism.

Amino Acid Sequence↗