Karin M. Keller
University of Texas at Austin
Network
Latest external collaboration on country level. Dive into details by clicking on the dots.
Publication
Featured researches published by Karin M. Keller.
Biochemistry | 2012
Clint D. J. Tavares; John P. O'Brien; Olga Abramczyk; Ashwini K. Devkota; Kevin S. Shores; Scarlett B. Ferguson; Tamer S. Kaoud; Mangalika Warthaka; Kyle D. Marshall; Karin M. Keller; Yan Zhang; Jennifer S. Brodbelt; Bulent Ozpolat; Kevin N. Dalby
Eukaryotic elongation factor 2 kinase (eEF-2K) is an atypical protein kinase regulated by Ca(2+) and calmodulin (CaM). Its only known substrate is eukaryotic elongation factor 2 (eEF-2), whose phosphorylation by eEF-2K impedes global protein synthesis. To date, the mechanism of eEF-2K autophosphorylation has not been fully elucidated. To investigate the mechanism of autophosphorylation, human eEF-2K was coexpressed with λ-phosphatase and purified from bacteria in a three-step protocol using a CaM affinity column. Purified eEF-2K was induced to autophosphorylate by incubation with Ca(2+)/CaM in the presence of MgATP. Analyzing tryptic or chymotryptic peptides by mass spectrometry monitored the autophosphorylation over 0-180 min. The following five major autophosphorylation sites were identified: Thr-348, Thr-353, Ser-445, Ser-474, and Ser-500. In the presence of Ca(2+)/CaM, robust phosphorylation of Thr-348 occurs within seconds of addition of MgATP. Mutagenesis studies suggest that phosphorylation of Thr-348 is required for substrate (eEF-2 or a peptide substrate) phosphorylation, but not self-phosphorylation. Phosphorylation of Ser-500 lags behind the phosphorylation of Thr-348 and is associated with the Ca(2+)-independent activity of eEF-2K. Mutation of Ser-500 to Asp, but not Ala, renders eEF-2K Ca(2+)-independent. Surprisingly, this Ca(2+)-independent activity requires the presence of CaM.
Biomedical Chromatography | 2012
Y-J Xue; Brian Melo; Martha Vallejo; Yuwen Zhao; Lina Tang; Yuan-Shek Chen; Karin M. Keller
We proposed an integrated bioanalytical method development and validation approach: (1) method screening based on analytes physicochemical properties and metabolism information to determine the most appropriate extraction/analysis conditions; (2) preliminary stability evaluation using both quality control and incurred samples to establish sample collection, storage and processing conditions; (3) mock validation to examine method accuracy and precision and incurred sample reproducibility; and (4) method validation to confirm the results obtained during method development. This integrated approach was applied to the determination of compound I in rat plasma and compound II in rat and dog plasma. The effectiveness of the approach was demonstrated by the superior quality of three method validations: (1) a zero run failure rate; (2) >93% of quality control results within 10% of nominal values; and (3) 99% incurred sample within 9.2% of the original values. In addition, rat and dog plasma methods for compound II were successfully applied to analyze more than 900 plasma samples obtained from Investigational New Drug (IND) toxicology studies in rats and dogs with near perfect results: (1) a zero run failure rate; (2) excellent accuracy and precision for standards and quality controls; and (3) 98% incurred samples within 15% of the original values.
Journal of the American Chemical Society | 2011
Han-Yuan Gong; Brett M. Rambo; Elizabeth Karnas; Vincent M. Lynch; Karin M. Keller; Jonathan L. Sessler
Journal of the American Oil Chemists' Society | 2012
Jessica Jones; Schonna R. Manning; Morela Montoya; Karin M. Keller; Martin Poenie
Analytical Biochemistry | 2004
Karin M. Keller; Jennifer S. Brodbelt
Journal of the American Chemical Society | 2013
Han-Yuan Gong; Brett M. Rambo; Vincent M. Lynch; Karin M. Keller; Jonathan L. Sessler
Journal of Mass Spectrometry | 2005
Karin M. Keller; Junmei Zhang; Leon P. Oehlers; Jennifer S. Brodbelt
Chemistry: A European Journal | 2012
Han-Yuan Gong; Brett M. Rambo; Vincent M. Lynch; Karin M. Keller; Jonathan L. Sessler
Journal of Mass Spectrometry | 2005
Karin M. Keller; Megan M. Breeden; Junmei Zhang; Andrew D. Ellington; Jennifer S. Brodbelt
Journal of the American Society for Mass Spectrometry | 2005
Karin M. Keller; Jennifer S. Brodbelt