The substrate degradome of meprin metalloproteases reveals an unexpected proteolytic link between meprin β and ADAM10.

The in vivo roles of meprin metalloproteases in pathophysiological conditions remain elusive. Substrates define protease roles. Therefore, to identify natural substrates for human meprin α and β we employed TAILS (terminal amine isotopic labeling of substrates), a proteomics approach that enriches for N-terminal peptides of proteins and cleavage fragments. Of the 151 new extracellular substrates we identified, it was notable that ADAM10 (a disintegrin and metalloprotease domain-containing protein 10)-the constitutive α-secretase-is activated by meprin β through cleavage of the propeptide. To validate this cleavage event, we expressed recombinant proADAM10 and after preincubation with meprin β, this resulted in significantly elevated ADAM10 activity. Cellular expression in murine primary fibroblasts confirmed activation. Other novel substrates including extracellular matrix proteins, growth factors and inhibitors were validated by western analyses and enzyme activity assays with Edman sequencing confirming the exact cleavage sites identified by TAILS. Cleavages in vivo were confirmed by comparing wild-type and meprin(-/-) mice. Our finding of cystatin C, elafin and fetuin-A as substrates and natural inhibitors for meprins reveal new mechanisms in the regulation of protease activity important for understanding pathophysiological processes.

Crystal structure of the Leishmania major phosphodiesterase LmjPDEB1 and insight into the design of the parasite-selective inhibitors

Human leishmaniasis is a major public health problem in many countries, but chemotherapy is in an unsatisfactory state. Leishmania major phosphodiesterases (LmjPDEs) have been shown to play important roles in cell proliferation and apoptosis of the parasite. Thus LmjPDE inhibitors may potentially represent a novel class of drugs for the treatment of leishmaniasis. Reported here are the kinetic characterization of the LmjPDEB1 catalytic domain and its crystal structure as a complex with 3-isobutyl-1-methylxanthine (IBMX) at 1.55 A resolution. The structure of LmjPDEB1 is similar to that of human PDEs. IBMX stacks against the conserved phenylalanine and forms a hydrogen bond with the invariant glutamine, in a pattern common to most inhibitors bound to human PDEs. However, an extensive structural comparison reveals subtle, but significant differences between the active sites of LmjPDEB1 and human PDEs. In addition, a pocket next to the inhibitor binding site is found to be unique to LmjPDEB1. This pocket is isolated by two gating residues in human PDE families, but constitutes a natural expansion of the inhibitor binding pocket in LmjPDEB1. The structure particularity might be useful for the development of parasite-selective inhibitors for the treatment of leishmaniasis.

Endogenous and synthetic MMP inhibitors in CNS physiopathology.

Matrix metalloproteinases (MMPs, including the membrane-type MMPs (MT-MMPs)), a disintegrin and metalloproteinase (ADAM), and ADAM with thrombospondin motifs belong to the metzincins, a subclass of metalloproteinases that contain a Met residue and a Zn(2+) ion at the catalytic site necessary for enzymatic reaction. MMP proteolytic activity is mainly controlled by their natural tissue inhibitors of metalloproteinase (TIMP). A number of synthetic inhibitors have been developed to control deleterious MMP activity. The roles of MMPs and some of their ECM substrates in CNS physiology and pathology are covered by other chapters of the present volume and will thus not be addressed in depth. This chapter will focus (i) on the endogenous MMP inhibitors in the CNS, (ii) on MMP and TIMP regulations in three large classes of neuropathologic processes (inflammatory, neurodegenerative, and infectious), and (iii) on synthetic inhibitors of MMPs and the perspective of their use in different brain diseases.

Correlating FAAH and anandamide cellular uptake inhibition using N-alkylcarbamate inhibitors: from ultrapotent to hyperpotent.

Besides the suggested role of a putative endocannabinoid membrane transporter mediating the cellular uptake of the endocannabinoid anandamide (AEA), this process is intrinsically coupled to AEA degradation by the fatty acid amide hydrolase (FAAH). Differential blockage of each mechanism is possible using specific small-molecule inhibitors. Starting from the natural product-derived 2E,4E-dodecadiene scaffold previously shown to interact with the endocannabinoid system (ECS), a series of diverse N-alkylcarbamates were prepared with the aim of generating novel ECS modulators. While being inactive at cannabinoid receptors and monoacylglycerol lipase, these N-alkylcarbamates showed potent to ultrapotent picomolar FAAH inhibition in U937 cells. Overall, a highly significant correlation (Spearman's rho=0.91) was found between the inhibition of FAAH and AEA cellular uptake among 54 compounds. Accordingly, in HMC-1 cells lacking FAAH expression the effect on AEA cellular uptake was dramatically reduced. Unexpectedly, 3-(4,5-dihydrothiazol-2-yl)phenyl carbamates and the 3-(1,2,3-thiadiazol-4-yl)phenyl carbamates WOBE490, WOBE491 and WOBE492 showed a potentiation of cellular AEA uptake inhibition in U937 cells, resulting in unprecedented femtomolar (hyperpotent) IC50 values. Potential methodological issues and the role of cellular accumulation of selected probes were investigated. It is shown that albumin impacts the potency of specific N-alkylcarbamates and, more importantly, that accumulation of FAAH inhibitors can significantly increase their effect on cellular AEA uptake. Taken together, this series of N-alkylcarbamates shows a FAAH-dependent inhibition of cellular AEA uptake, which can be strongly potentiated using specific head group modifications. These findings provide a rational basis for the development of hyperpotent AEA uptake inhibitors mediated by ultrapotent FAAH inhibition.