Structure-based dissection of the active site chemistry of leukotriene A4 hydrolase: implications for M1 aminopeptidases and inhibitor design

M1 aminopeptidases comprise a large family of biologically important zinc enzymes. We show that peptide turnover by the M1 prototype, leukotriene A4 hydrolase/aminopeptidase, involves a shift in substrate position associated with exchange of zinc coordinating groups, while maintaining the overall coordination geometry. The transition state is stabilized by residues conserved among M1 members and in the final reaction step, Glu-296 of the canonical zinc binding HEXXH motif shuffles a proton from the hydrolytic water to the leaving group. Tripeptide substrates bind along the conserved GXMEN motif, precisely occupying the distance between Glu-271 and Arg-563, whereas the Arg specificity is governed by a narrow S1 pocket capped with Asp-375. Our data provide detailed insights to the active site chemistry of M1 aminopeptidases and will aid in the development of novel enzyme inhibitors.     

An Artificial Heme Enzyme for Cyclopropanation Reactions

An artificial heme enzyme was created through self‐assembly from hemin and the lactococcal multidrug resistance regulator (LmrR). The crystal structure shows the heme bound inside the hydrophobic pore of the protein, where it appears inaccessible for substrates. However, good catalytic activity and moderate enantioselectivity was observed in an abiological cyclopropanation reaction. We propose that the dynamic nature of the structure of the LmrR protein is key to the observed activity. This was supported by molecular dynamics simulations, which showed transient formation of opened conformations that allow the binding of substrates and the formation of pre‐catalytic structures.     

Inhibition of cyclin-dependent kinases, GSK-3beta and CK1 by hymenialdisine, a marine sponge constituent

BACKGROUND: Over 2000 protein kinases regulate cellular functions. Screening for inhibitors of some of these kinases has already yielded some potent and selective compounds with promising potential for the treatment of human diseases. RESULTS: The marine sponge constituent hymenialdisine is a potent inhibitor of cyclin-dependent kinases, glycogen synthase kinase-3beta and casein kinase 1. Hymenialdisine competes with ATP for binding to these kinases. A CDK2-hymenialdisine complex crystal structure shows that three hydrogen bonds link hymenialdisine to the Glu81 and Leu83 residues of CDK2, as observed with other inhibitors. Hymenialdisine inhibits CDK5/p35 in vivo as demonstrated by the lack of phosphorylation/down-regulation of Pak1 kinase in E18 rat cortical neurons, and also inhibits GSK-3 in vivo as shown by the inhibition of MAP-1B phosphorylation. Hymenialdisine also blocks the in vivo phosphorylation of the microtubule-binding protein tau at sites that are hyperphosphorylated by GSK-3 and CDK5/p35 in Alzheimer's disease (cross-reacting with Alzheimer's-specific AT100 antibodies). CONCLUSIONS: The natural product hymenialdisine is a new kinase inhibitor with promising potential applications for treating neurodegenerative disorders.     

Synthesis and Diels-Alder Reactions of a New Kind of Chiral Dienophiles: Cyclic Vinyl-p-tolylsulfilimines

A new kind of chiral dienophiles, cyclic vinyl-p-tolylsulfilimines (2a and 2b), were obtained from the corresponding (Z)-sulfinylacrylonitriles with HBF(4) and methanol. The asymmetric Diels-Alder reaction of optically pure 2a with cyclopentadiene under mild thermal or catalyzed conditions afforded only the endo-4a adduct with complete endo and pi-facial selectivities. The ability of the sulfilimine moiety to enhance the dienophilic reactivity of the double bond is similar to that of the sulfinyl group.     

Causal loop diagrams as a de-escalation technique

Escalation of commitment, the tendency of decision makers to keep on investing in losing courses of action, has been shown to be a costly decision bias that affects many areas of decision making. Even though escalation is a widely studied phenomenon, there has been comparatively little research on how to avoid this bias. The present study focuses on de-escalation of commitment and proposes that causal loop diagrams (CLDs) can help to decrease escalating commitment to a failing course of action. By means of an experiment, this study shows that using a CLD decreases escalation tendencies.