Determining origin in a migratory marine vertebrate: a novel method to integrate stable isotopes and satellite tracking.

Stable isotope analysis is a useful tool to track animal movements in both terrestrial and marine environments. These intrinsic markers are assimilated through the diet and may exhibit spatial gradients as a result of biogeochemical processes at the base of the food web. In the marine environment, maps to predict the spatial distribution of stable isotopes are limited, and thus determining geographic origin has been reliant upon integrating satellite telemetry and stable isotope data. Migratory sea turtles regularly move between foraging and reproductive areas. Whereas most nesting populations can be easily accessed and regularly monitored, little is known about the demographic trends in foraging populations. The purpose of the present study was to examine migration patterns of loggerhead nesting aggregations in the Gulf of Mexico (GoM), where sea turtles have been historically understudied. Two methods of geographic assignment using stable isotope values in known-origin samples from satellite telemetry were compared: (1) a nominal approach through discriminant analysis and (2) a novel continuous-surface approach using bivariate carbon and nitrogen isoscapes (isotopic landscapes) developed for this study. Tissue samples for stable isotope analysis were obtained from 60 satellite-tracked individuals at five nesting beaches within the GoM. Both methodological approaches for assignment resulted in high accuracy of foraging area determination, though each has advantages and disadvantages. The nominal approach is more appropriate when defined boundaries are necessary, but up to 42% of the individuals could not be considered in this approach. All individuals can be included in the continuous-surface approach, and individual results can be aggregated to identify geographic hotspots of foraging area use, though the accuracy rate was lower than nominal assignment. The methodological validation provides a foundation for future sea turtle studies in the region to inexpensively determine geographic origin for large numbers of untracked individuals. Regular monitoring of sea turtle nesting aggregations with stable isotope sampling can be used to fill critical data gaps regarding habitat use and migration patterns. Probabilistic assignment to origin with isoscapes has not been previously used in the marine environment, but the methods presented here could also be applied to other migratory marine species.

Modeling of receptor mimics that inhibit superantigen pathogenesis.

Staphylococcal enterotoxins SEB and SEC3 and toxic shock syndrome toxin TSST-1 act as superantigens by overstimulating the human immune system and thereby compromise host defense. The mechanism of pathogenesis is explained on the basis of superantigen binding to the MHC class II receptor on the antigen presenting cell and to the T cell receptor (TcR) on the T cell. SEB, SEC3 and TSST-1 bind as intact proteins and make contacts with the alpha1 subdomain (DRalpha) of MHC class II and Vbeta subdomain of TcR. SEB, SEC3 and TSST-1 show specificities for different TcRVbeta isoforms. We have designed three different chimeras linking the same DRalpha with different TcRVbeta isoforms to specifically target SEB, SEC3 and TSST-1 and inhibit their pathogenesis. Here, we show by molecular modeling that the DRalpha, TcRVbeta and linker of a given chimera interact with the target superantigen in a type-specific manner. An initial model of the complex is constructed on the basis of observed inter-molecular contacts between DRalpha/TcRVbeta and the superantigens. A constant temperature (300 K) 200 ps molecular dynamics is performed to sample different conformations of a chimera-superantigen complex by utilizing the flexibility of the (GSTAPPA)(2) linker while maintaining the native folds of superantigen, DRalpha and TcRVbeta and the observed intermolecular contacts. After equilibration, 100 molecular dynamic snapshots are minimized and analyzed. This provides descriptions of various pairwise interactions at the contact interface in the complex and important clues on single site mutations on the chimera that may enhance the stability of a given superantigen-chimera complex.