The Yersinia pestis autotransporter YapG contains a fast folding [beta]-helix domain

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Frazier, Monica L.
- Affiliation: School of Medicine, Department of Biochemistry and Biophysics

Abstract

Autotransporter proteins are the most widely secreted protein family in gram-negative bacteria; their passenger domains are predicted to be [beta]-helical in 97% of cases. The [beta]-helical fold has been hitherto understudied with respect to protein folding, which typically is centered on small [alpha]-helical, low contact order proteins. In contrast, the [beta]-helical portions of passenger domains are typically large, and made up of unique structural repeats with high contact order. Here, we have studied the in vitro folding of the passenger domain of YapG, an autotransporter from Yersinia pestis, via thermodynamic and kinetic approaches. We have identified YapG as the fastest refolding passenger domain to date. Steady-state fluorescence and circular dichroism indicate a one-step folding process; however, stopped-flow fluorescence indicates a one-step unfolding and a two-step refolding. Neither proline isomerization nor aggregation is associated with YapG refolding, suggesting this fast folding [beta]-helix may experience a general collapse followed by a slower fine tuning folding step. In addition, gel filtration studies of the refolded state indicate that YapG may refold into two different folded species. Taken together, these results provide the first biophysical analysis of an autotransporter passenger domain from Y. pestis and provide new insight into the folding process in [beta]-helical folds.

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... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Biochemistry and Biophysics.

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