Corey M Johnson, Thomas W Linsky, Dae-Wi Yoon, Maria D Person, Walter Fast
Division of Medicinal Chemistry, College of Pharmacy, University of Texas, Austin, Texas 78712, United States.
Journal of the American Chemical Society 2011 Feb 9In an effort to develop novel covalent modifiers of dimethylarginine dimethylaminohydrolase (DDAH) that are useful for biological applications, a set of "fragment"-sized inhibitors that were identified using a high-throughput screen are tested for time-dependent inhibition. One structural class of inactivators, 4-halopyridines, show time- and concentration-dependent inactivation of DDAH, and the inactivation mechanism of one example, 4-bromo-2-methylpyridine (1), is characterized in detail. The neutral form of halopyridines is not very reactive with excess glutathione. However, 1 readily reacts, with loss of its halide, in a selective, covalent, and irreversible manner with the active-site Cys249 of DDAH. This active-site Cys is not particularly reactive (pK(a) ca. 8.8), and 1 does not inactivate papain (Cys pK(a) ca. ≤4), suggesting that, unlike many reagents, Cys nucleophilicity is not a predominating factor in selectivity. Rather, binding and stabilization of the more reactive pyridinium form of the inactivator by a second moiety, Asp66, is required for facile reaction. This constraint imparts a unique selectivity profile to these inactivators. To our knowledge, halopyridines have not previously been reported as protein modifiers, and therefore they represent a first-in-class example of a novel type of quiescent affinity label.
Corey M Johnson, Thomas W Linsky, Dae-Wi Yoon, Maria D Person, Walter Fast. Discovery of halopyridines as quiescent affinity labels: inactivation of dimethylarginine dimethylaminohydrolase. Journal of the American Chemical Society. 2011 Feb 9;133(5):1553-62
PMID: 21222447
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