In This Issue


1453

Devlina Chakravarty, Mainak Guharoy, Charles H Robert, Pinak Chakrabarti and Joël Janin

When two macromolecules form a complex, part of their surface becomes inaccessible to solvent, but the BSA (buried surface area) measured on the complex may not represent that decrease in accessible surface area (the DSA) if conformation changes accompany association. Taking 144 protein-protein complexes for which the free component structures are known, we observe that the two quantities can differ by over 20%, and more surprisingly, that the BSA generally exceeds the DSA (by 7.2% on average) even when the conformation changes are small, due to local atomic movements optimizing intermolecular at the expense of internal contacts.

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1349

Saskia Vanderhaegen, Marcus Fislage, Katarzyna Domanska, Wim Versées, Els Pardon, Vittorio Bellotti and Jan Steyaert

For many proteins, abnormal structure or metabolism results in self-aggregation, causing the formation of fibrillar structures and amyloid fibrils. Unfortunately, the structural characterization of early aggregation-prone monomeric species remains a challenge. To investigate early intermediates of β2-microglobulin (β2m) amyloidosis in human, we trapped the Pro32Gly amyloidogenic variant of β2m as a monomer and solved its structure by nanobody-assisted X-ray crystallography. The structure reveals a trans peptide bond at position 32, whereas Pro32 adopts the cis conformation in the wild type monomer. This cis to trans isomerization at Pro32 triggers several structural changes that convert β2-microglobulin in an aggregation-prone monomeric species.

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1313

Austin E. Smith, Mohona Sarkar, Gregory B. Young and Gary J. Pielak

NMR-detected amide-proton exchange is a powerful tool for assessing protein stability. A requirement for its straightforward use under physiological conditions is that the intracellular environment has an insignificant effect on the exchange rates of unstructured peptides. As a prelude to studies in living cells, Smith et al. quantified exchange rates in the unstructured regions of the small globular protein, chymotrypsin inhibitor 2, in Escherichia coli lysates. They found that the effect is indeed small, as indicated by the observation of protection factors (i.e. rate in lysate over that in buffer) of less than five.

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1392

Brian P. Wellensiek, Andrew C. Larsen, Julia Flores, Bertram L. Jacobs and John C. Chaput

Post-translational modifications define how proteins function in cells. However, most human proteins are synthesized in bacterial systems that lack the capacity to modify proteins. In the current issue, Wellensiek et al. describe a cytoplasmic expression system that allows for efficient synthesis in human cells. The approach employs an in vitro evolved translation enhancing element that eliminates the need for complex genetic engineering. The authors demonstrate that proteins of different lengths and classifications can be synthesized from linear or plasmid DNA, making their system ideal for most routine expression needs or high throughput production.

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