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PubMed1996

Identification of glutamate residues essential for catalytic activity and zinc coordination in aminopeptidase A.

Aminopeptidase A (EC 3.4.11.7, APA) is a homodimeric membrane-bound glycoprotein that contains the consensus sequence HEXXH(385-389) found in zinc metallopeptidases such as thermolysin. The x-ray structure of the latter enzyme revealed that the two histidines of this motif are two of the three zinc-coordinating ligands and that the glutamate is a crucial amino acid involved in catalysis. Alignment of the sequence of mouse APA with those of the already characterized metallopeptidases showed the presence of several conserved amino acids such as a glutamate residue in position 408 which may constitute the putative third zinc ligand. The functional implication of this residue and the role of glutamate 386 in the HELVH(385-389) motif of APA have been investigated by replacing these residues with an aspartate (Asp-386, Asp-408) or an alanine (Ala-386, Ala-408) by site-directed mutagenesis. Expressed mutated proteins in position 386 showed no APA activity. Ala-408 was also inactive, and Asp-408 had 5% of the wild type enzyme activity and a similar Km. 65Zn incorporation measurements indicated that Ala-386 binds the zinc ion as well as the wild type enzyme, whereas the Ala-408 mutant did not. These results provide evidence that Glu-408 is the third zinc-coordinating residue of APA, confirm the presumed involvement of Glu-386 in the catalytic process of the enzyme, and identify APA as a zinc metallopeptidase functionally similar to thermolysin.

Amino Acid Sequence↗
PubMed1999

Yeast methionine aminopeptidase I. Alteration of substrate specificity by site-directed mutagenesis.

In eukaryotes, two isozymes (I and II) of methionine aminopeptidase (MetAP) catalyze the removal of the initiator methionine if the penultimate residue has a small radius of gyration (glycine, alanine, serine, threonine, proline, valine, and cysteine). Using site-directed mutagenesis, recombinant yeast MetAP I derivatives that are able to cleave N-terminal methionine from substrates that have larger penultimate residues have been expressed. A Met to Ala change at 329 (Met206 in Escherichia coli enzyme) produces an average catalytic efficiency 1.5-fold higher than the native enzyme on normal substrates and cleaves substrates containing penultimate asparagine, glutamine, isoleucine, leucine, methionine, and phenylalanine. Interestingly, the native enzyme also has significant activity with the asparagine peptide not previously identified as a substrate. Mutation of Gln356 (Gln233 in E. coli MetAP) to alanine results in a catalytic efficiency about one-third that of native with normal substrates but which can cleave methionine from substrates with penultimate histidine, asparagine, glutamine, leucine, methionine, phenylalanine, and tryptophan. Mutation of Ser195 to alanine had no effect on substrate specificity. None of the altered enzymes produced cleaved substrates with a fully charged residue (lysine, arginine, aspartic acid, or glutamic acid) or tyrosine in the penultimate position.

Aminopeptidases↗
PubMed2000

Insulin-responsive aminopeptidase trafficking in 3T3-L1 adipocytes.

The insulin-responsive aminopeptidase (IRAP/VP165/gp160) was identified originally in GLUT4-containing vesicles and shown to translocate in response to insulin, much like the glucose transporter 4 (GLUT4). This study characterizes the trafficking and kinetics of IRAP in exocytosis, endocytosis, and recycling to the membrane in 3T3-L1 adipocytes. After exposure of 3T3-L1 adipocytes to insulin, IRAP translocated to the plasma membrane as assessed by either cell fractionation, surface biotinylation, or the plasma membrane sheet assay. The rate of exocytosis closely paralleled that of GLUT4. In the continuous presence of insulin, IRAP was endocytosed with a half-time of about 3-5 min. IRAP endocytosis is inhibited by cytosol acidification, a property of clathrin-mediated endocytosis, but not by the expression of a constitutively active Akt/PKB. Arrival in an LDM fraction derived via subcellular fractionation exhibited a slower time course than disappearance from the cell surface, suggesting additional endocytic intermediates. As assayed by membrane "sheets," GLUT4 and IRAP showed similar internalization rates that are wortmannin-insensitive and occur with a half-time of roughly 5 min. IRAP remaining on the cell surface 10 min following insulin removal was both biotin- and avidin-accessible, implying the absence of thin-necked invaginations. Finally, endocytosed IRAP quickly recycled back to the plasma membrane in a wortmannin-sensitive process. These results demonstrate rapid endocytosis and recycling of IRAP in the presence of insulin and trafficking that matches GLUT4 in rate.

3T3 Cells↗
PubMed2001

Evidence that the angiotensin IV (AT(4)) receptor is the enzyme insulin-regulated aminopeptidase.

Central infusion of angiotensin IV or its more stable analogues facilitates memory retention and retrieval in normal animals and reverses amnesia induced by scopolamine or by bilateral perforant pathway lesions. These peptides bind with high affinity and specificity to a novel binding site designated the angiotensin AT(4) receptor. Until now, the AT(4) receptor has eluded molecular characterization. Here we identify the AT(4) receptor, by protein purification and peptide sequencing, to be insulin-regulated aminopeptidase (IRAP). HEK 293T cells transfected with IRAP exhibit typical AT(4) receptor binding characteristics; the AT(4) receptor ligands, angiotensin IV and LVV-hemorphin 7, compete for the binding of [(125)I]Nle(1)-angiotensin IV with IC(50) values of 32 and 140 nm, respectively. The distribution of IRAP and its mRNA in the brain, determined by immunohistochemistry and hybridization histochemistry, parallels that of the AT(4) receptor determined by radioligand binding. We also show that AT(4) receptor ligands dose-dependently inhibit the catalytic activity of IRAP. We have therefore demonstrated that the AT(4) receptor is IRAP and propose that AT(4) receptor ligands may exert their effects by inhibiting the catalytic activity of IRAP thereby extending the half-life of its neuropeptide substrates.

Aminopeptidases↗
PubMed2003

Proteomics-based target identification: bengamides as a new class of methionine aminopeptidase inhibitors.

LAF389 is a synthetic analogue of bengamides, a class of marine natural products that produce inhibitory effects on tumor growth in vitro and in vivo. A proteomics-based approach has been used to identify signaling pathways affected by bengamides. LAF389 treatment of cells resulted in altered mobility of a subset of proteins on two-dimensional gel electrophoresis. Detailed analysis of one of the proteins, 14-3-3gamma, showed that bengamide treatment resulted in retention of the amino-terminal methionine, suggesting that bengamides directly or indirectly inhibited methionine aminopeptidases (MetAps). Both known MetAps are inhibited by LAF389. Short interfering RNA suppression of MetAp2 also altered amino-terminal processing of 14-3-3gamma. A high resolution structure of human MetAp2 co-crystallized with a bengamide shows that the compound binds in a manner that mimics peptide substrates. Additionally, the structure reveals that three key hydroxyl groups on the inhibitor coordinate the di-cobalt center in the enzyme active site.

14-3-3 Proteins↗
PubMed2004

GLUT4 overexpression or deficiency in adipocytes of transgenic mice alters the composition of GLUT4 vesicles and the subcellular localization of GLUT4 and insulin-responsive aminopeptidase.

The majority of GLUT4 is sequestered in unique intracellular vesicles in the absence of insulin. Upon insulin stimulation GLUT4 vesicles translocate to, and fuse with, the plasma membrane. To determine the effect of GLUT4 content on the distribution and subcellular trafficking of GLUT4 and other vesicle proteins, adipocytes of adipose-specific, GLUT4-deficient (aP2-GLUT4-/-) mice and adipose-specific, GLUT4-overexpressing (aP2-GLUT4-Tg) mice were studied. GLUT4 amount was reduced by 80-95% in aP2-GLUT4-/- adipocytes and increased approximately 10-fold in aP2-GLUT4-Tg adipocytes compared with controls. Insulin-responsive aminopeptidase (IRAP) protein amount was decreased 35% in aP2-GLUT4-/- adipocytes and increased 45% in aP2-GLUT4-Tg adipocytes. VAMP2 protein was also decreased by 60% in aP2-GLUT4-/- adipocytes and increased 2-fold in aP2-GLUT4-Tg adipocytes. IRAP and VAMP2 mRNA levels were unaffected in aP2-GLUT4-Tg, suggesting that overexpression of GLUT4 affects IRAP and VAMP2 protein stability. The amount and subcellular distribution of syntaxin4, SNAP23, Munc-18c, and GLUT1 were unchanged in either aP2-GLUT4-/- or aP2-GLUT4-Tg adipocytes, but transferrin receptor was partially redistributed to the plasma membrane in aP2-GLUT4-Tg adipocytes. Immunogold electron microscopy revealed that overexpression of GLUT4 in adipocytes increased the number of GLUT4 molecules per vesicle nearly 2-fold and the number of GLUT4 and IRAP-containing vesicles per cell 3-fold. In addition, the proportion of cellular GLUT4 and IRAP at the plasma membrane in unstimulated aP2-GLUT4-Tg adipocytes was increased 4- and 2-fold, respectively, suggesting that sequestration of GLUT4 and IRAP is saturable. Our results show that GLUT4 overexpression or deficiency affects the amount of other GLUT4-vesicle proteins including IRAP and VAMP2 and that GLUT4 sequestration is saturable.

Adipocytes↗
PubMed2004

Mutations at the S1 sites of methionine aminopeptidases from Escherichia coli and Homo sapiens reveal the residues critical for substrate specificity.

Methionine aminopeptidase (MetAP) catalyzes the removal of methionine from newly synthesized polypeptides. MetAP carries out this cleavage with high precision, and Met is the only natural amino acid residue at the N terminus that is accepted, although type I and type II MetAPs use two different sets of residues to form the hydrophobic S1 site. Characteristics of the S1 binding pocket in type I MetAP were investigated by systematic mutation of each of the seven S1 residues in Escherichia coli MetAP type I (EcMetAP1) and human MetAP type I (HsMetAP1). We found that Tyr-65 and Trp-221 in EcMetAP1, as well as the corresponding residues Phe-197 and Trp-352 in HsMetAP1, were essential for the hydrolysis of a thiopeptolide substrate, Met-S-Gly-Phe. Mutation of Phe-191 to Ala in HsMetAP1 caused inactivity in contrast to the full activity of EcMetAP1(Y62A), which may suggest a subtle difference between the two type I enzymes. The more striking finding is that mutation of Cys-70 in EcMetAP1 or Cys-202 in HsMetAP1 opens up the S1 pocket. The thiopeptolides Leu-S-Gly-Phe and Phe-S-Gly-Phe, with previously unacceptable Leu or Phe as the N-terminal residue, became efficient substrates of EcMetAP1(C70A) and HsMetAP1(C202A). The relaxed specificity shown in these S1 site mutants for the N-terminal residues was confirmed by hydrolysis of peptide substrates and inhibition by reaction products. The structural features at the enzyme active site will be useful information for designing specific MetAP inhibitors for therapeutic applications.

Amino Acid Sequence↗
PubMed2004

The catalytic role of glutamate 151 in the leucine aminopeptidase from Aeromonas proteolytica.

Glutamate 151 has been proposed to act as the general acid/base during the peptide hydrolysis reaction catalyzed by the co-catalytic metallohydrolase from Aeromonas proteolytica (AAP). However, to date, no direct evidence has been reported for the role of Glu-151 during catalytic turnover by AAP. In order to elucidate the catalytic role of Glu-151, altered AAP enzymes have been prepared in which Glu-151 has been substituted with a glutamine, an alanine, and an aspartate. The Michaelis constant (K(m)) does not change upon substitution to aspartate or glutamine, but the rate of the reaction changes drastically in the following order: glutamate (100% activity), aspartate (0.05%), glutamine (0.004%), and alanine (0%). Examination of the pH dependence of the kinetic constants k(cat) and K(m) revealed a change in the pK(a) of a group that ionizes at pH 4.8 in recombinant leucine aminopeptidase (rAAP) to 4.2 for E151D-AAP. The remaining pK(a) values at 5.2, 7.5, and 9.9 do not change. Proton inventory studies indicate that one proton is transferred in the rate-limiting step of the reaction at pH 10.50 for both rAAP and E151D-AAP, but at pH 6.50 two protons and general solvation effects are responsible for the observed effects in the reaction catalyzed by rAAP and E151D-AAP, respectively. Based on these data, Glu-151 is intrinsically involved in the peptide hydrolysis reaction catalyzed by AAP and can be assigned the role of a general acid and base.

Aeromonas↗
PubMed2005

Yeast glutamine-fructose-6-phosphate aminotransferase (Gfa1) requires methionine aminopeptidase activity for proper function.

Methionine aminopeptidase (MetAP) catalyzes the co-translational processing of initiator methionine from nascent proteins. A cellular requirement for MetAP activity is likely due to dysfunction of MetAP substrates that require methionine removal for proper protein function. Glutamine-fructose-6-phosphate aminotransferase (Gfa1) is an essential enzyme in yeast that catalyzes the first and rate-limiting step in hexosamine biosynthesis. The alpha-amino group of Gfa1 Cys-1 has been proposed to act as a nucleophile in the catalytic mechanism. We used two mutational strategies to evaluate whether removal of initiator methionine, catalyzed by MetAP, is required for Gfa1 function. Our results demonstrate that exposure of the alpha-amino group of Cys-1 is required for normal Gfa1 function as failure to do so results in decreased enzyme activity and slow growth. Further, either isoform of MetAP in yeast is sufficient for Gfa1 processing in vivo. These results are the first demonstration of an endogenous yeast protein that requires the exposure of the alpha-amino group by MetAP action for normal function. Additionally, Gfa1 will be a relevant target in therapeutic or physiological applications in which MetAP activity is inhibited.

Aminopeptidases↗
PubMed1992

A nephritogenic rat monoclonal antibody to mouse aminopeptidase A. Induction of massive albuminuria after a single intravenous injection.

Antibodies directed against antigens present on renal epithelial cells can cause membranous glomerulonephritis in experimental animals, which closely resembles the human form of this disease. However, most antibodies produced so far fail to cause the persistent and severe proteinuria that is seen in humans. In our search for new antibodies of this kind, we have now produced a monoclonal antibody (mAb) against mouse aminopeptidase A, a hydrolase that is present in the mouse kidney. The mAb (ASD-4) was prepared by fusion of mouse myeloma cells with splenocytes of Lou rats immunized with brush border (BB) membranes from mouse kidneys. ASD-4 is of the IgG1 subclass and reacts with a 140-kD protein as demonstrated by immunoprecipitation on radiolabeled BB membranes. In indirect immunofluorescence and immunoelectronmicroscopy of normal mouse kidneys, ASD-4 was diffusely present on the BB of the S1 and S2 segments of the proximal tubules, and on the cell membranes of the glomerular visceral epithelia. It also bound to cell membranes of nonglomerular endothelia, smooth muscle cells of arteries, and juxtaglomerular cells. After injection of ASD-4 into normal mice, an immediate homogeneous binding to the capillary wall was seen that gradually changed into a fine granular pattern after 1 d. This glomerular binding was followed by binding to the BB and basolateral membranes of the convoluted proximal tubules. Immediately after injection of ASD-4, a dose-dependent albuminuria occurred that lasted for at least 16 d. ASD-4 is thus a new rat mAb against a well-defined renal epithelial antigen that causes not only membranous glomerulonephritis after a single injection in the mouse, but also severe albuminuria.

Albuminuria↗
PubMed1995

Regulation of B cell precursor proliferation by aminopeptidase A.

The BP-1/6C3 molecule expressed by early B lineage cells and some stromal cells has been identified as aminopeptidase A (APA). We have previously demonstrated that IL-7 selectively induces BP-1/APA expression by pre-B cells coincident with their growth. Here we directly demonstrate that BP-1 is preferentially expressed by the proliferating subpopulation of normal B cell progenitors. Furthermore, when non-adherent BALB/c bone marrow cells were incubated with IL-7 in the presence of purified BP-1 antibody, B cell precursor proliferation was markedly inhibited. Modulation of the BP-1/6C3 antigen did not occur in the presence of the BP-1 antibody, but APA enzymatic activity was significantly inhibited. The 6C3 antibody, which recognizes a different epitope on the APA molecule, had no effect on either B cell precursor proliferation or APA enzyme activity. We hypothesized that neutralization of APA by the BP-1 antibody results in inhibition of IL-7 driven B cell precursor proliferation. However, when isolated 14.8+ bone marrow cells were cultured with IL-7 in the presence of the BP-1 antibody, no inhibition of proliferation occurred. This data suggested that the effect of the BP-1 antibody might be related to the action of APA on peptides in the marrow microenvironment which are not present in cultures of isolated B cell precursors. The addition of irradiated non-adherent bone marrow cells to the 14.8+ cell cultures restored the inhibitory effect of the BP-1 antibody. Based on these observations, we propose that APA cleaves a small peptide which serves as a natural inhibitor of B cell precursor proliferation.

Aminopeptidases↗
PubMed2000

Renal expression of aminopeptidase A in rats with two-kidney, one-clip hypertension.

BACKGROUND: Angiotensin II (ANG II) is a major factor involved in the progression of chronic renal disease. Although the generation of this vasoactive peptide has been investigated in great detail, only a few studies have hitherto addressed the metabolism of ANG II into fragments such as angiotensin III and IV (ANG III, IV) which may exert physiological effects independent of ANG II. Aminopeptidase A (APA) is the major enzyme degrading ANG II. The aim of the current study was to evaluate glomerular APA expression in rats with two-kidney, one-clip hypertension. METHODS: The left renal artery was restricted with a 0.2-mm silver clip. Kidneys were harvested 1 and 4 weeks after surgery. APA enzyme and protein expression was evaluated in kidney sections. Total APA enzyme activity and mRNA expression was assessed in isolated glomeruli. Degradation of exogenous ANG II by isolated glomeruli was measured with reverse-phase high-performance liquid chromatography. RESULTS: APA enzyme activity, protein, and mRNA expression were stimulated in the clipped kidney 1 week after surgery compared with the contralateral kidney or normal controls. In contrast, 4 weeks after clipping APA activity and expression was higher in the contralateral kidney. In parallel to these findings, degradation of ANG II was greatest in isolated glomeruli obtained from the clipped kidney after 1 week. However, preparations from the contralateral kidney 4 weeks after surgery were more active in the metabolism of exogenous ANG II. CONCLUSION: The present study provides evidence that APA is complexly regulated in in vivo situations with an activated local renin-ANG II system. ANG II appears to play a direct role in this regulation. However, since conversion of ANG II to ANG III by APA is the initial step leading to the formation of ANG IV which may exert detrimental effects not mediated through classical ANG II receptors, a local increase in APA activity may contribute to the progression of chronic renal disease even during complete AT(1)-receptor blockade.

Aminopeptidases↗
PubMed1997

Methionine aminopeptidase from the hyperthermophilic Archaeon Pyrococcus furiosus: molecular cloning and overexpression in Escherichia coli of the gene, and characteristics of the enzyme.

A gene for a methionine aminopeptidase (MAP; EC 3.4.11.18), which catalyzes the removal of amino-terminal methionine from the growing peptide chain on the ribosome, has been cloned from the hyperthermophilic Archaeon, Pyrococcus furiosus, by a novel method effectively using its cosmid protein library, sequenced and expressed in Escherichia coli. The DNA sequence encodes a protein containing 295 amino acid residues with methionine at the N-terminus. From protein analyses of the recombinant protein expressed in E. coli, by using both amino acid sequence analysis from the N-terminus by automated Edman degradation and analyses of molecular masses of the peptides generated by two enzymatic cleavages performed independently, digestions with lysylendopeptidase and Endoproteinase Asp-N, with ionspray mass spectrometry, the primary structure of the protein has been elucidated to be completely identical with that deduced from its DNA sequence. Comparison of the amino acid sequence of P. furiosus MAP (P.f. MAP) with those of other MAPs from Eukarya and Bacteria showed that the protein has a high degree of sequence homology in the stretches surrounding the five cobalt-binding residues fully preserved in all of MAPs determined so far, but P.f. MAP belongs to Type II because it has an extra long insertion of about 60 amino acid residues between the fourth and fifth cobalt-binding ligands, similar to MAPs from human and rat, and to Met-AP2 from Saccharomyces cerevisiae, in comparison to Type I MAPs from Bacteria. Therefore, P.f. MAP seems to be rather close to those from Eukarya, although it is distinct in lacking the N-terminal extension of about 90-150 residues universally found in MAPs from Eukarya. These findings suggest that P.f. MAP is evolutionally located at the Eukarya-Bacteria boundary. The enzyme expressed in E. coli exhibits a considerable thermostability, with a half-life of approximately 4.5 h at 90 degrees C and an optimum temperature of around 90 degrees C.

Amino Acid Sequence↗
PubMed1986

Inhibitory effects of various synthetic substrates for aminopeptidases on phagocytosis of immune complexes by macrophages.

The inhibitory effects of various 7-(aminoacyl)-4-methylcoumarinylamides (AA-MCA's), synthetic substrates for aminopeptidases, on phagocytosis of immune complexes by guinea pig peritoneal macrophages were investigated by measuring the intracellular uptake of sensitized 51Cr-sheep erythrocytes and 125I-alpha-amylase complexed with homologous IgG2 antibody. Among the AA-MCA's examined, MCA compounds of hydrophobic amino acids (Phe, Tyr, Leu, and Pro) were found to inhibit the intracellular uptake and digestion of immune complexes. Sucrose density gradient centrifugation of the homogenates of macrophages treated with the inhibitors for 1 h at 37 degrees C showed that they modulated the lysosomes, resulting in a decrease in buoyant density of the organella. These effects of the inhibitors on the buoyant density of the lysosomes as well as on the phagocytic activity of macrophages disappeared upon removal of the inhibitors from the cells by washing. Since none of 7-amino-4-methylcoumarin, L-phenylalanine, and bestatin methyl ester could significantly inhibit the phagocytosis of immune complexes by macrophages, the MCA compounds of hydrophobic amino acids appear to inhibit the phagocytosis as a consequence of their lysosomotropic nature.

Amino Acids↗
PubMed1998

Inhibition of vasopressinergic neurons by central injection of a specific aminopeptidase A inhibitor.

The brain angiotensin (Ang) system plays an important role in the central control of vasopressin release. Using EC33, a selective aminopeptidase A inhibitor which blocks the metabolism of Ang II in Ang III, we previously reported that vasopressin release was under the control of Ang III and not Ang II. To determine accurately the action of EC33, the effects of intracerebroventricular injection of Ang peptides or EC33 on extracellular unit activity of vasopressinergic neurons in the supraoptic nucleus of urethane-anaesthetized rats were examined. Angiotensin II (15-30 ng) or Ang III (15 ng) increased the firing rate of all neurons tested. Conversely, EC33 (10 microg) reduced or completely abolished (30-60 microg) the basal firing rate for 4-6 min in all eight neurons tested. EC33 (30 microg) also inhibited the activity induced by 30 ng Ang II. It was concluded that the observed activity of Ang II required its conversion to Ang III and that endogenous Ang III may exert a tonic control on the basal firing level of vasopressinergic neurons.

Aminopeptidases↗
PubMed1988

Change in plasma cystyl aminopeptidase (oxytocinase) between 30-34 weeks' gestation as a predictor of pregnancy-induced hypertension.

Ninety-two primigravidas were screened biweekly by measurement of plasma cystyl aminopeptidase from 28 weeks' gestation until delivery. Fourteen developed hypertension with or without proteinuria after 36 weeks. The hypertensive group had significantly higher levels of the enzyme at 30 weeks, although this difference was not significant at 34 weeks. The rise in the hypertensive group was less than 50% between weeks 30-34 in all cases, whereas it was over 50% in all but two of the 43 controls. The difference in the rates of increase of the enzyme and its action on antidiuretic hormone may have some bearing on the subsequent development of hypertension.

Adult↗
PubMed1995

A non-essential glutamyl aminopeptidase is required for optimal growth of Lactococcus lactis MG1363 in milk.

Degenerate PCR primers were designed from the N-terminal amino acid sequence of a glutamyl aminopeptidase (PepA) from Lactococcus lactis. These primers were used to screen a lambda library for clones containing the gene (pepA) encoding PepA. The DNA sequence of a 2.1 kb fragment containing pepA was determined. The sequence revealed the presence of one complete and two incomplete open reading frames (ORFs). The complete ORF encodes a putative protein of 353 amino acids with a predicted N-terminal sequence identical to that determined for purified PepA. The pepA gene was subcloned on an Escherichia coli plasmid vector and production of active PepA was confirmed by means of a zymogram. Mutants of L. lactis in which the pepA gene was inactivated grew to normal cell densities in milk but exhibited a reduced growth rate during the exponential phase. Thus whilst PepA is required for optimal growth it is not essential.

Amino Acid Sequence↗
PubMed2006

Structural analysis of metalloform-selective inhibition of methionine aminopeptidase.

One of the challenges in the development of methionine aminopeptidase (MetAP) inhibitors as antibacterial and anticancer agents is to define the metal ion actually used by MetAP in vivo and to discover MetAP inhibitors that can inhibit the metalloform that is relevant in vivo. Two distinct classes of novel nonpeptidic MetAP inhibitors that are not only potent but also highly selective for either the Mn(II) or Co(II) form have been identified. Three crystal structures of Escherichia coli MetAP complexed with the metalloform-selective inhibitors 5-(2,5-dichlorophenyl)furan-2-carboxylic acid (2), 5-[2-(trifluoromethyl)phenyl]furan-2-carboxylic acid (3) and N-cyclopentyl-N-(thiazol-2-yl)oxalamide (4) have been solved and analysis of these structures has revealed the structural basis for their metalloform-selective inhibition. The Mn(II)-form selective inhibitors (2) and (3) both use their carboxylate group to coordinate with the two Mn(II) ions at the dinuclear metal site and both adopt a non-coplanar conformation for the two aromatic rings. The unique coordination geometry of these inhibitors may determine their Mn(II)-form selectivity. In contrast, the Co(II)-form selective inhibitor (4) recruits an unexpected third metal ion, forming a trimetallic enzyme-metal-inhibitor complex. Thus, an important factor in the selectivity of (4) for the Co(II) form may be a consequence of a greater preference for a softer N,O-donor ligand for the softer Co(II).

Aminopeptidases↗