3.4.22.B50 apoenzyme and enzyme in complexes with ubiquitin, and inhibitors 5-amino-2-methyl-N-[(1R)-1-(naphthalen-1-yl)ethyl]benzamide, N-(1,3-benzodioxol-5-ylmethyl)-1-[(1R)-1-(naphthalen-1-yl)ethyl]piperidine-4-carboxamide, N-(4-fluorobenzyl)-1-[(1R)-1-(naphthalen-1-yl)ethyl]piperidine-4-carboxamide, and N-(3-fluorobenzyl)-1-[(1R)-1-(naphthalen-1-yl)ethyl]piperidine-4-carboxamide, sitting drop vapor diffusion method, apoenzyme by mixing of 1.1-20 mg/ml protein in 20 mM Tris, pH 7.5, 10 mM DTT, with 100 mM sodium citrate, pH 5.2, 3 M ammonium sulfate. Enzyme-inhibitor N-(1,3-benzodioxol-5-ylmethyl)-1-[(1R)-1-(naphthalen-1-yl)ethyl]piperidine-4-carboxamide complex by mixing of 5 mg/ml protein in 20 mM Tris, pH 7.5, 10 mM DTT, with 1 mM inhibitor, 1 M (NH4)2SO4, 50 mM MES, pH 6.5, and 2.5% PEG 400. Enzyme-inhibitor 5-amino-2-methyl-N-[(1R)-1-(naphthalen-1-yl)ethyl]benzamide by mixing of 8 mg/ml protein in 20 mM Tris, pH 7.5, 10 mM DTT with 0.20 mM inhibitor, 1 M LiCl2, 0.1 M MES pH 6.0, 30% PEG 6000. Enzyme-inhibitor N-(3-fluorobenzyl)-1-[(1R)-1-(naphthalen-1-yl)ethyl]piperidine-4-carboxamide or N-(4-fluorobenzyl)-1-[(1R)-1-(naphthalen-1-yl)ethyl]piperidine-4-carboxamide complex by mixing of 6 and 12 mg/ml protein, respectively, in 25 mM Tris, pH 7.5, 100 mM NaCl, 10 mM DTT with 0.20 mM inhibitor, 100 mM sodium citrate, pH 5.5, 40% v/v PEG 600. Enzyme-ubiquitin complex by mixing of 3-12 mg/ml protein and ubiquitin in 20 mM Tris, pH 7.5, with 0.1 M CHES, pH 9.5, 18% PEG 3000, X-ray diffraction structure determination and analysis at 1.4-2.75 A resolution 3.4.22.B50 hanging drop vapor diffusion method, using 100 mM Bis-Tris, pH 6.5, 25-30% (w/v) polyethylene glycol monomethyl ether 2000 3.4.22.B50 hanging-drop vapor-diffusion, to 1.85 A resolution, the enzyme has an intact zinc-binding motif, an unobstructed catalytically competent active site and an intriguing, ubiquitin-like N-terminal domain 3.4.22.B50 in complex with ubiquitin, hanging drop vapor diffusion method, using 100 mM MES, pH 6.2, 18% (w/v) polyethylene glycol 20,000 3.4.22.B50 modeling of structure 3.4.22.B50 purified enzyme mutant C112S in complex with ubiquitin, sitting drop vapour diffusion method, mixing of enzyme and ubiquitin in a 1:1 molar ratio giving 8 mg/ml and 2 mg/ml, respectively, addition of a reservoir solution consisting of 18% PEG 3000, 0.1 M CHES, pH 9.5, 22°C, X-ray diffraction structure determination and analysis at 1.4 A resolution