Interactions of β-Helical Antifreeze Protein Mutants with Ice

The fold of the β-helical antifreeze protein from Tenebrio molitor (TmAFP) proved to be surprisingly tolerant of multiple amino acid substitutions, enabling the construction of a panel of mutants displaying grids of single amino acid types in place of the threonines on the ice-binding face. These mutants, maintaining the regularity of amino acid spacing found in the wild-type protein but with different functional groups on the surface, were tested for antifreeze activity by measuring thermal hysteresis and observing ice grown in their presence. We found that no mutant exhibited the dramatic activity of the wild-type version of this hyperactive antifreeze protein. However, mutants containing four valines or tyrosines in place of the threonines in the center of the TmAFP ice-binding face showed residual thermal hysteresis activity and had marked effects on ice crystal morphology. The results are discussed in the context of a two-stage model for the absorption−inhibition mechanism of antifreeze protein binding to ice surfaces

Phylogenetics and enzymology of plant quiescin sulfhydryl oxidase

AbstractQuiescin Sulfhydryl Oxidase (QSOX), a catalyst of disulfide bond formation, is found in both plants and animals. Mammalian, avian, and trypanosomal QSOX enzymes have been studied in detail, but plant QSOX has yet to be characterized. Differences between plant and animal QSOXs in domain composition and active-site sequences raise the question of whether these QSOXs function by the same mechanism. We demonstrate that Arabidopsis thaliana QSOX produced in bacteria is folded and functional as a sulfhydryl oxidase but does not exhibit the interdomain electron transfer observed for its animal counterpart. Based on this finding, further exploration into the respective roles of the redox-active sites in plant QSOX and the reason for their concatenation is warranted

Memory Functioning for Personally Experienced and Witnessed Events in Children with Autism and the Implications for Educators, Mental Health Professionals, and the Law

Several researchers have hypothesized a deficit in memory processing to exist in children with a diagnosis of autism spectrum disorder (ASD). This hypothesis has been supported by findings of deficient recall and recognition ability in children with ASD. Specifically, research has pointed to greater deficits in their ability to recall events related to the self as opposed to others. However, such research has not explored how memory functioning would be impacted when an event with an emotional tenor was used and when a forced choice yes/no paradigm was used to extricate what was remembered from the event. The current study aimed to compare recognition memory for personally experienced and witnessed events using a mock stranger-danger scenario. Forty-two children with ASD underwent either a personally experienced or witnessed event. Following the event, the child was administered a survey assessing their recognition of both thematic and detailed content from the event. No statistically significant differences were identified for recognition memory between the personally experienced and witnessed events. While differences between the groups were not found to be significant, it was revealed that there was a trend towards significance for better recognition of details for the witnessed than for the personally experienced event. Implications for future research are discussed as well as the potential impact of such findings in the terms of forensic and educational domains

Structure and electron-transfer pathway of the human methionine sulfoxide reductase MsrB3

Introduction: The post-translational oxidation of methionine to methionine sulfoxide is a reversible process, enabling repair of oxidative damage to proteins and the use of sulfoxidation as a regulatory switch. Methionine sulfoxide reductases catalyze the stereospecific reduction of methionine sulfoxide. One of the mammalian methionine sulfoxide reductases, MsrB3, has a signal sequence for entry into the endoplasmic reticulum (ER). In the ER, MsrB3 is expected to encounter a distinct redox environment compared to its paralogs in the cytosol, nucleus, and mitochondria. Aims: We sought to determine the location and arrangement of MsrB3 redox-active cysteines, which may couple MsrB3 activity to other redox events in the ER. Results: We determined the human MsrB3 structure using X-ray crystallography. The structure revealed that a disulfide bond near the protein amino terminus is distant in space from the active site. Nevertheless, biochemical assays showed that these amino-terminal cysteines are oxidized by the MsrB3 active site after its reaction with methionine sulfoxide. Innovation: This study reveals a mechanism to shuttle oxidizing equivalents from the primary MsrB3 active site toward the enzyme surface, where they would be available for further dithiol-disulfide exchange reactions. Conclusion: Conformational changes must occur during the MsrB3 catalytic cycle to transfer oxidizing equivalents from the active site to the amino-terminal redox-active disulfide. The accessibility of this exposed disulfide may help couple MsrB3 activity to other dithiol/disulfide redox events in the secretory pathway

Ribosome-associated vesicles: A dynamic subcompartment of the endoplasmic reticulum in secretory cells

The endoplasmic reticulum (ER) is a highly dynamic network of membranes. Here, we combine live-cell microscopy with in situ cryo–electron tomography to directly visualize ER dynamics in several secretory cell types including pancreatic β-cells and neurons under near-native conditions. Using these imaging approaches, we identify a novel, mobile form of ER, ribosome-associated vesicles (RAVs), found primarily in the cell periphery, which is conserved across different cell types and species. We show that RAVs exist as distinct, highly dynamic structures separate from the intact ER reticular architecture that interact with mitochondria via direct intermembrane contacts. These findings describe a new ER subcompartment within cells

The protein structures underlying receptor binding and membrane fusion of ecotropic murine leukemia viruses

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 1997.Vita.Includes bibliographical references (leaves 131-132).by Deborah Fall.Ph.D