Short-lived alpha-helical intermediates in the folding of beta-sheet proteins.

Several lines of evidence point strongly toward the importance of highly alpha-helical intermediates in the folding of all globular proteins, regardless of their native structure. However, experimental refolding studies demonstrate no observable alpha-helical intermediate during refolding of some beta-sheet proteins and have dampened enthusiasm for this model of protein folding. In this study, beta-sheet proteins were hypothesized to have potential to form amphiphilic helices at a period of <3.6 residues/turn that matches or exceeds the potential at 3.6 residues/turn. Hypothetically, such potential is the basis for an effective and unidirectional mechanism by which highly alpha-helical intermediates might be rapidly disassembled during folding and potentially accounts for the difficulty in detecting highly alpha-helical intermediates during the folding of some proteins. The presence of this potential was confirmed, indicating that a model entailing ubiquitous formation of alpha-helical intermediates during the folding of globular proteins predicts previously unrecognized features of primary structure. Further, the folding of fatty acid binding protein, a predominantly beta-sheet protein that exhibits no apparent highly alpha-helical intermediate during folding, was dramatically accelerated by 2,2,2-trifluoroethanol, a solvent that stabilizes alpha-helical structure. This observation suggests that formation of an alpha-helix can be a rate-limiting step during folding of a predominantly beta-sheet protein and further supports the role of highly alpha-helical intermediates in the folding of all globular proteins.

Working at the interface of phylogenetics and population genetics: a biogeographical analysis of Triaenops spp. (Chiroptera: Hipposideridae).

New applications of genetic data to questions of historical biogeography have revolutionized our understanding of how organisms have come to occupy their present distributions. Phylogenetic methods in combination with divergence time estimation can reveal biogeographical centres of origin, differentiate between hypotheses of vicariance and dispersal, and reveal the directionality of dispersal events. Despite their power, however, phylogenetic methods can sometimes yield patterns that are compatible with multiple, equally well-supported biogeographical hypotheses. In such cases, additional approaches must be integrated to differentiate among conflicting dispersal hypotheses. Here, we use a synthetic approach that draws upon the analytical strengths of coalescent and population genetic methods to augment phylogenetic analyses in order to assess the biogeographical history of Madagascar's Triaenops bats (Chiroptera: Hipposideridae). Phylogenetic analyses of mitochondrial DNA sequence data for Malagasy and east African Triaenops reveal a pattern that equally supports two competing hypotheses. While the phylogeny cannot determine whether Africa or Madagascar was the centre of origin for the species investigated, it serves as the essential backbone for the application of coalescent and population genetic methods. From the application of these methods, we conclude that a hypothesis of two independent but unidirectional dispersal events from Africa to Madagascar is best supported by the data.

Identity Change Impacts Autobiographical Reconstruction of Identity-Relevant Events: Influences of the Self-System on Remembering

The focus on how one is behaving, feeling, and thinking, provides a powerful source of self-knowledge. How is this self-knowledge utilized in the dynamic reconstruction of autobiographical memories? How, in turn, might autobiographical memories support identity and the self-system? I address these questions through a critical review of the literature on autobiographical memory and the self-system, with a special focus on the self-concept, self-knowledge, and identity. I then outline the methods and results of a prospective longitudinal study examining the effects of an identity change on memory for events related to that identity. Participant-rated memory characteristics, computer-generated ratings of narrative content and structure, and neutral-observer ratings of coherence were examined for changes over time related to an identity-change, as well as for their ability to predict an identity-change. The conclusions from this study are threefold: (1) when the rated centrality of an event decreases, the reported instances of retrieval, as well as the phenomenology associated with retrieval and the number of words used to describe the memory, also decrease; (2) memory accuracy (here, estimating past behaviors) was not influenced by an identity change; and (3) remembering is not unidirectional – characteristics of identity-relevant memories and the life story predict and may help support persistence with an identity (here, an academic trajectory).