个人简介

Biochemistry & Molecular Biology B.S., 1988, Univ. of Washington Research Chemist, 1988-1990, FDA (Bothell,WA) Ph.D., 1997, Univ. of Washington NIH Postdoc. Research Fellow, 1997-2000, Research Assistant Professor, 2000-2003, Institute of Biological Chemistry, Washington State Univ. AwardOrganizationDivisionLevel CodeType CodeStart DateEnd Date Outstanding Graduate AdvisorProfessionalHonors2011 Ph.D.University of Washington, SeattleGraduateDegree1997 Bachelor of ScienceUniversity of Washington, SeattleUndergraduateDegree1988

研究领域

Biological Organic

(Research Description PDF - 881 kb) Interdisciplinary methods are used to evaluate the application of enzyme catalysts (acquired from various sources: bacteria, plants, yeast, etc.) with non-native substrates to transform natural compounds or synthetically-derived chemicals to novel products. The genes encoding these enzymes can be transferred to a suitable host organism to potentially produce in vivo an assortment of bioactive molecules. Paclitaxel (Taxol) Pathway Enzymes. Phenylalanine aminomutase (PAM) converts (2S)-α-phenylalanine to (3R)-β-phenylalanine and lies on the paclitaxel (Taxol?) biosynthetic pathway in Taxus yew plants. The complete stereochemistry, substrate specificity, and crystal structure data of the catalyst have been investigated. PAM also converts β-amino acids (3R)-β-phenylalanine and (3S)-β-phenylalanine (unnatural product) to (2S)-α-phenylalanine. Further studies include investigating the substrate selectivity and kinetics of mutant forms of PAM, assessing the cryptic mechanism that yields product stereochemistry, surveying binding isotope effects, and conducting structure/function assignments based on homology and X-ray crystallographic data. Taxus Acyltransferases (AT) of the BAHD Superfamily: The broad substrate specificity of these acyl-CoA-dependent ATs has been unveiled (below), and provides a Green source for the production of Taxol analogues. An extended objective of this project is to employ directed mutagenesis on a family of Taxus-derived ATs to define the function of the transferases; the resultant mutant enzymes will be assayed and ultimately characterized by crystallographic analysis. A conserved motif, His-X-X-X-Asp, is postulated to be involved in acyl group transfer to the acceptor molecule. The prevailing mechanism proposed for BAHD acyltransferases does not support our observation showing that the Taxus ATs catalyze intermolecular acyl group transfer from one substrate to another in the absence acyl-CoA. We are currently assessing the function of the catalytic residues by 18O-exchange methodology. Foreseeably, we will extend our investigation to evaluate the specificity of BAHD acyltransferases from other plants on novel aminated and hydroxylated surrogate substrates. Our current evaluation of a small set of Taxol pathway enzymes demonstrates that a broad survey of biocatalysts on any biosynthetic pathway is generally necessary to reveal their specificity and potential application to make product analogues. A new graduate student can embark on studies involving organic synthesis of novel surrogate substrates, molecular cloning techniques, expression of various enzymes in E. coli, assay development, basic biochemical applications and molecular biological approaches related to enzyme kinetics, enzyme purification and characterization, and various analytical techniques (NMR, GC/MS, LC-MS(/MS), etc.).

近期论文

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Genome sequencing and analysis of the paclitaxel-producing endophytic fungus Penicillium aurantiogriseum, Y. Yang; H. Zhao; R.A. Barrero; B. Zhang; G. Sun; I.W. Wilson; F. Xie; K.D. Walker; J.W. Parks; R. Bruce; et al., BMC Genomics, 2014, 15(1):69. A bacterial tyrosine aminomutase proceeds through retention or inversion of stereochemistry to catalyze its isomerization reaction, U. Wanninayake; K.D. Walker, J. Am. Chem.Soc. 2013, 135(30), 11193. Assessing the deamination rate of a covalent aminomutase adduct by burst phase analysis, U. Wanninayake; K.D. Walker, Biochemistry 2012, 51(26), 5226. Taxol biosynthesis: Tyrocidine synthetase a catalyzes the production of phenylisoserinyl coa and other amino phenylpropanoyl thioesters, R. Muchiri; K.D. Walker, Chemistry and Biology 2012, 19(6), 679. Insights into the mechanistic pathway of the Pantoea agglomerans phenylalanine aminomutase, Susan Strom; Udayanga Wanninayake; Nishanka Dilini Ratnayake; Kevin D. Walker; James H. Geiger, Ang. Chem. Int. Ed., 2012, 51(12), 2898. (S)-styryl-α-alanine used to probe the intermolecular mechanism of an intramolecular MIO-aminomutase, Udayanga Wanninayake; Yvonne Deporre; Mark Ondari; Kevin D. Walker, Biochemistry 2011, 50(46), 10082. Stereochemistry and mechanism of a microbial phenylalanine aminomutase, N. D. Ratnayake; U. Wanninayake; J.H. Geiger; K.D. Walker, J. Am. Chem. Soc. 2011, 133(22), 8531.