Membrane-bound glutamate carboxypeptidase II (GCPII) is a zinc metalloenzyme that catalyzes the hydrolysis of the neurotransmitter N-acetyl-L-aspartyl-L-glutamate (NAAG) to N-acetyl-L-aspartate and L-glutamate (which is itself a neurotransmitter). Potent and selective GCPII inhibitors have been shown to decrease brain glutamate and provide neuroprotection in preclinical models of stroke, amyotrophic lateral sclerosis, and neuropathic pain. Here, we report crystal structures of the extracellular part of GCPII in complex with both potent and weak inhibitors and with glutamate, the product of the enzyme's hydrolysis reaction, at 2.0, 2.4, and 2.2 Å resolution, respectively. GCPII folds into three domains: protease-like, apical, and C-terminal. All three participate in substrate binding, with two of them directly involved in C-terminal glutamate recognition. One of the carbohydrate moieties of the enzyme is essential for homodimer formation of GCPII. The three-dimensional structures presented here reveal an induced-fit substratebinding mode of this key enzyme and provide essential information for the design of GCPII inhibitors useful in the treatment of neuronal diseases and prostate cancer.

Urea-based, low molecular weight ligands of glutamate carboxypeptidase II (GCPII) have demonstrated efficacy in various models of neurological disorders and can serve as imaging agents for prostate cancer. To enhance further development of such compounds, we determined X-ray structures of four complexes between human GCPII and urea-based inhibitors at high resolution. All ligands demonstrate an invariant glutarate moiety within the S1′ pocket of the enzyme. The ureido linkage between P1 and P1′ inhibitor sites interacts with the active-site Zn12+ ion and the side chains of Tyr552 and His553. Interactions within the S1 pocket are defined primarily by a network of hydrogen bonds between the P1 carboxylate group of the inhibitors and the side chains of Arg534, Arg536, and Asn519. Importantly, we have identified a hydrophobic pocket accessory to the S1 site that can be exploited for structure-based design of novel GCPII inhibitors with increased lipophilicity.

Calcium-binding RTX proteins are equipped with C-terminal secretion signals and translocate from the Ca(2+)-depleted cytosol of Gram-negative bacteria directly into the Ca(2+)-rich external milieu, passing through the "channel-tunnel" ducts of type I secretion systems (T1SSs). Using Bordetella pertussis adenylate cyclase toxin, we solved the structure of an essential C-terminal assembly that caps the RTX domains of RTX family leukotoxins. This is shown to scaffold directional Ca(2+)-dependent folding of the carboxy-proximal RTX repeat blocks into β-rolls. The resulting intramolecular Brownian ratchets then prevent backsliding of translocating RTX proteins in the T1SS conduits and thereby accelerate excretion of very large RTX leukotoxins from bacterial cells by a vectorial "push-ratchet" mechanism. Successive Ca(2+)-dependent and cosecretional acquisition of a functional RTX toxin structure in the course of T1SS-mediated translocation, through RTX domain folding from the C-terminal cap toward the N terminus, sets a paradigm that opens for design of virulence inhibitors of major pathogens.

Glutamate carboxypeptidase II (GCPII, EC 3.4.17.21) is a membrane peptidase expressed in a number of tissues such as kidney, prostate and brain. The brain form of GCPII (also known as NAALADase) cleaves N-acetyl-aspartyl glutamate to yield free glutamate. Animal model experiments show that inhibition of GCPII prevents neuronal cell death during experimental ischaemia. GCPII thus represents an important target for the treatment of neuronal damage caused by excess glutamate. In this paper we report expression of an extracellular portion of human glutamate carboxypeptidase II (amino acids 44±750) in Drosophila Schneider's cells and its puri®-cation to homogeneity. A novel assay for hydrolytic activity of recombinant human GCPII (rhGCPII), based on¯uorimetric detection of released alpha-amino groups was established, and used for its enzymological characterization. rhGCPII does not show dipeptidylpeptidase IV-like activity assigned to the native form of the enzyme previously. Using a complete set of protected dipeptides, substrate speci®city of rhGCPII was elucidated. In addition to the previously described substrates, four novel compounds, Ac-Glu-Met, Ac-Asp-Met and, surprisingly, Ac-Ala-Glu and Ac-Ala-Met were identi®ed as substrates for GCPII, and their respective kinetic constants determined. The glycosylation of rhGCPII was found indispensable for the enzymatic activity. Keywords: enzyme glycosylation, glutamate carboxypeptidase II, NAALADase, neuroprotection, zinc metallopeptidase. Membrane glutamate carboxypeptidase II (GCPII) is a metalloproteinase expressed in various tissues and organs (Berger et al. 1995;Chang et al. 1999). Its proteolytic activity was ®rstly recognized in brain cells, where it has been shown to be responsible for the cleavage of N-acetyl-Laspartyl-L-glutamate (NAAG) yielding free glutamate in the extracellular space. Based on the initial characterization of its substrate speci®city, the enzyme was termed N-acetylated alpha-linked-acidic-dipeptidase (NAALADase; Robinson et al. 1987).NAAG is an abundant neuropeptide found in millimolar concentrations in the brain (Coyle 1997). It is a mixed agonist/antagonist at N-methyl-D-aspartate ionotropic receptors and an agonist at the group II metabotropic glutamate receptors (mGlu; Wroblewska et al. 1993Wroblewska et al. , 1997. After release from pre-synaptic terminals, NAAG diffuses from the synaptic cleft and is rapidly hydrolysed by GCPII located on adjacent astrocytes. Free glutamate subsequently acts at the various glutamate receptor subtypes. Excessive receptor activation by glutamate is thought to be at least partially responsible for the neuronal injury caused by stroke (Fagg and Foster 1986). Inhibition of NAAG metabolism was suggested as a possible strategy to attenuate excitatory amino Abbreviations used: Ac, acetyl group; AMC, 7-amino-4-methylcoumarine; DIEA, diisopropylethylamine; DPM, disintegrations per minute; DPP IV, dipeptidyl peptidase IV; FAB-MS, fast atom bombardment mass spectrometry; FBS, foetal bovine serum; Fmoc, 9-...

Glutamate carboxypeptidase II (GCPII) is a membrane-bound binuclear zinc metallopeptidase with the highest expression levels found in the nervous and prostatic tissue. Throughout the nervous system, glia-bound GCPII is intimately involved in the neuron-neuron and neuron-glia signaling via the hydrolysis of N-acetylaspartylglutamate (NAAG), the most abundant mammalian peptidic neurotransmitter. The inhibition of the GCPII-controlled NAAG catabolism has been shown to attenuate neurotoxicity associated with enhanced glutamate transmission and GCPII-specific inhibitors demonstrate efficacy in multiple preclinical models including traumatic brain injury, stroke, neuropathic and inflammatory pain, amyotrophic lateral sclerosis, and schizophrenia. The second major area of pharmacological interventions targeting GCPII focuses on prostate carcinoma; GCPII expression levels are highly increased in androgen-independent and metastatic disease. Consequently, the enzyme serves as a potential target for imaging and therapy. This review offers a summary of GCPII structure, physiological functions in healthy tissues, and its association with various pathologies. The review also outlines the development of GCPII-specific small-molecule compounds and their use in preclinical and clinical settings.

Prostate specific membrane antigen (PSMA) is a membrane-bound glutamate carboxypeptidase overexpressed in many forms of prostate cancer. Our laboratory has recently disclosed a class of small molecules, called ARM-Ps (antibody-recruiting molecule targeting prostate cancer) that are capable of enhancing antibody-mediated immune recognition of prostate cancer cells. Interestingly, during the course of these studies, we found ARM-Ps to exhibit extraordinarily high potencies toward PSMA, compared to previously reported inhibitors. Here, we report in-depth biochemical, crystallographic, and computational investigations which elucidate the origin of the observed affinity enhancement. These studies reveal a previously unreported arene-binding site on PSMA, which we believe participates in an aromatic stacking interaction with ARMs. Although this site is composed of only a few amino acid residues, it drastically enhances small molecule binding affinity. These results provide critical insights into the design of PSMA-targeted small molecules for prostate cancer diagnosis and treatment; more broadly, the presence of similar arene-binding sites throughout the proteome could prove widely enabling in the optimization of small-molecule-protein interactions.

Histone deacetylase 11 (HDAC11) is a sole member of the class IV HDAC subfamily with negligible intrinsic deacetylation activity. Here, we report in vitro profiling of HDAC11 deacylase activities, and our data unequivocally show that the enzyme efficiently removes acyl moieties spanning 8-18 carbons from the side chain nitrogen of the lysine residue of a peptidic substrate. Additionally, N-linked lipoic acid and biotin are removed by the enzyme, although with lower efficacy. Catalytic efficiencies toward dodecanoylated and myristoylated peptides were 77 700 and 149 000 M s, respectively, making HDAC11 the most proficient fatty-acid deacylase of the HDAC family. Interestingly, HDAC11 is strongly inhibited by free myristic, palmitic, and stearic acids with inhibition constants of 6.5, 0.9, and 1.6 μM, respectively. At the same time, its deacylase activity is stimulated more than 2.5-fold by both palmitoyl-coenzyme A and myristoyl-coenzyme A, pointing toward metabolic control of the enzymatic activity by fatty-acid metabolites. Our data reveal novel enzymatic activity of HDAC11 that can, in turn, facilitate the uncovering of additional biological functions of the enzyme as well as the design of isoform-specific HDAC inhibitors.

Histone deacetylases (HDACs) are involved in diverse cellular regulatory mechanisms including non-canonical functions outside the chromatin environment. Several publications have demonstrated that selective HDAC inhibitors (HDACi) can influence tumor immunogenicity and the functional activity of specific immune cells. In particular, the selective inhibition of HDAC6 has been reported to decrease tumor growth in several malignancies. However, there is still no clarity about the cellular components mediating this effect. In this study, we evaluated the HDAC6i Nexturastat A as a priming agent to facilitate the transition of the tumor microenvironment from “cold” to “hot”, and potentially augment immune check-point blockade therapies. This combination modality demonstrated to significantly reduce tumor growth in syngeneic melanoma tumor models. Additionally, we observed a complete neutralization of the up-regulation of PD-L1 and other immunosuppressive pathways induced by the treatment with anti-PD-1 blockade. This combination also showed profound changes in the tumor microenvironment such as enhanced infiltration of immune cells, increased central and effector T cell memory, and a significant reduction of pro-tumorigenic M2 macrophages. The evaluation of individual components of the tumor microenvironment suggested that the in vivo anti-tumor activity of HDAC6i is mediated by its effect on tumor cells and tumor-associated macrophages, and not directly over T cells. Overall, our results indicate that selective HDAC6i could be used as immunological priming agents to sensitize immunologically “cold” tumors and subsequently improve ongoing immune check-point blockade therapies.