Yingssu Tsai

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The carboxysome is a bacterial organelle that functions to enhance the efficiency of CO2 fixation by encapsulating the enzymes ribulose bisphosphate carboxylase/oxygenase (RuBisCO) and carbonic anhydrase. The outer shell of the carboxysome is reminiscent of a viral capsid, being constructed from many copies of a few small proteins. Here we describe the(More)
Prior site-directed mutagenesis studies in bacterial ketosteroid isomerase (KSI) reported that substitution of both oxyanion hole hydrogen bond donors gives a 10(5)- to 10(8)-fold rate reduction, suggesting that the oxyanion hole may provide the major contribution to KSI catalysis. But these seemingly conservative mutations replaced the oxyanion hole(More)
Within the idiosyncratic enzyme active-site environment, side chain and ligand pKa values can be profoundly perturbed relative to their values in aqueous solution. Whereas structural inspection of systems has often attributed perturbed pKa values to dominant contributions from placement near charged groups or within hydrophobic pockets, Tyr57 of a(More)
We compared the binding affinities of ground state analogues for bacterial ketosteroid isomerase (KSI) with a wild-type anionic Asp general base and with uncharged Asn and Ala in the general base position to provide a measure of potential ground state destabilization that could arise from the close juxtaposition of the anionic Asp and hydrophobic steroid in(More)
Although the cation-pi pair, formed between a side chain or substrate cation and the negative electrostatic potential of a pi system on the face of an aromatic ring, has been widely discussed and has been shown to be important in protein structure and protein-ligand interactions, there has been little discussion of the potential structural and functional(More)
Higher throughput methods to mount and collect data from multiple small and radiation-sensitive crystals are important to support challenging structural investigations using microfocus synchrotron beamlines. Furthermore, efficient sample-delivery methods are essential to carry out productive femtosecond crystallography experiments at X-ray free-electron(More)
W e report that the kinetic constants for several mutants of ketosteroid isomerase (KSI) from our 2011 publication are incorrect. Jason Schwans and Daniel Herschlag, the paper's first and corresponding authors, take full responsibility for and deeply regret these errors. Based on extensive control experiments, the errors likely arose from low levels(More)
The positioning of catalytic groups within proteins plays an important role in enzyme catalysis, and here we investigate the positioning of the general base in the enzyme ketosteroid isomerase (KSI). The oxygen atoms of Asp38, the general base in KSI, were previously shown to be involved in anion-aromatic interactions with two neighboring Phe residues. Here(More)
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