a δ38 deletion variant of human transketolase as a model of transketolase-like protein 1 exhibits no enzymatic activityδ38删除变异的人类转酮醇酶作为模型transketolase-like蛋白1展览没有酶活性.pdfVIP

A D38 Deletion Variant of Human Transketolase as a Model of Transketolase-Like Protein 1 Exhibits No Enzymatic Activity ¨ ¨ Stefan Schneider, Stefan Ludtke, Kathrin Schroder-Tittmann, Cindy Wechsler, Danilo Meyer, Kai Tittmann* ¨ ¨ Albrecht-von-Haller-Institute and Gottingen Center for Molecular Biosciences, Department of Bioanalytics, Georg-August-University Gottingen, Germany Abstract Besides transketolase (TKT), a thiamin-dependent enzyme of the pentose phosphate pathway, the human genome encodes for two closely related transketolase-like proteins, which share a high sequence identity with TKT. Transketolase-like protein 1 (TKTL1) has been implicated in cancerogenesis as its cellular expression levels were reported to directly correlate with invasion efficiency of cancer cells and patient mortality. It has been proposed that TKTL1 exerts its function by catalyzing an unusual enzymatic reaction, a hypothesis that has been the subject of recent controversy. The most striking difference between TKTL1 and TKT is a deletion of 38 consecutive amino acids in the N-terminal domain of the former, which constitute part of the active site in authentic TKT. Our structural and sequence analysis suggested that TKTL1 might not possess transketolase activity. In order to test this hypothesis in the absence of a recombinant expression system for TKTL1 and resilient data on its biochemical properties, we have engineered and biochemically characterized a ‘‘pseudo-TKTL1’’ D38 deletion variant of human TKT (TKTD38) as a viable model of TKTL1. Although the isolated protein is properly folded under in vitro conditions, both thermal stability as well as stability of the TK