RESUMO
Bacteria can defend themselves against beta-lactam antibiotics through the expression of class B beta-lactamases, which cleave the beta-lactam amide bond and render the molecule harmless. There are three subclasses of class B beta-lactamases (B1, B2, and B3), all of which require Zn2+ for activity and can bind either one or two zinc ions. Whereas the B1 and B3 metallo-beta-lactamases are most active as dizinc enzymes, subclass B2 enzymes, such as Aeromonas hydrophila CphA, are inhibited by the binding of a second zinc ion. We crystallized A. hydrophila CphA in order to determine the binding site of the inhibitory zinc ion. X-ray data from zinc-saturated crystals allowed us to solve the crystal structures of the dizinc forms of the wild-type enzyme and N220G mutant. The first zinc ion binds in the cysteine site, as previously determined for the monozinc form of the enzyme. The second zinc ion occupies a slightly modified histidine site, where the conserved His118 and His196 residues act as metal ligands. This atypical coordination sphere probably explains the rather high dissociation constant for the second zinc ion compared to those observed with enzymes of subclasses B1 and B3. Inhibition by the second zinc ion results from immobilization of the catalytically important His118 and His196 residues, as well as the folding of the Gly232-Asn233 loop into a position that covers the active site.
Assuntos
Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Histidina/química , Zinco/química , Zinco/metabolismo , beta-Lactamases/química , beta-Lactamases/metabolismo , Aeromonas hydrophila/enzimologia , Proteínas de Bactérias/genética , Sítios de Ligação/genética , Varredura Diferencial de Calorimetria , Dicroísmo Circular , Cristalografia por Raios X , Cinética , Mutagênese Sítio-Dirigida , Ligação Proteica/genética , Estrutura Secundária de Proteína , beta-Lactamases/genéticaRESUMO
Uteroglobin (UG) is a conserved protein which is induced by progesterone and secreted by the epithelia of various mammalian reproductive and respiratory organs. Recombinant bovine uteroglobin (recbUG), consisting of 80 amino acids with a C-terminal His6 tag, was overexpressed in Escherichia coli and purified. The protein was crystallized in two geometric forms, rhomboid and cuneate (wedge-shaped), by the hanging-drop vapour-diffusion method at 295 K. The rhomboid crystals diffracted to a maximum resolution of 1.6 A using synchrotron radiation. These crystals belong to space group P2(1)2(1)2, with unit-cell parameters a = 81.42, b = 82.82, c = 45.26 A, and contain four monomers per asymmetric unit. The cuneate crystals diffracted to 2.35 A resolution using a rotating-anode generator. These crystals belong to space group C222(1), with unit-cell parameters a = 43.39, b = 93.94, c = 77.30 A, and contain two molecules per asymmetric unit.
Assuntos
Uteroglobina/química , Animais , Bovinos , Cristalização , Cristalografia por Raios X , Escherichia coli/genética , Escherichia coli/metabolismo , Conformação Proteica , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismo , Uteroglobina/genética , Uteroglobina/isolamento & purificação , Uteroglobina/metabolismoRESUMO
Small antibody fragments are more useful than full-size antibodies for achieving efficient biodistribution. As a first step towards the design of a clinically desirable antibody fragment, the crystallization of a human V(H) fragment has been achieved. The fragment was derived from the single-chain antibody scFvM12, which recognizes a cancer-specific hypoglycosylated form of mucin. The V(H) fragment was obtained by in-drop digestion of the scFvM12 with a low concentration of the broad-spectrum protease subtilisin Carlsberg. The crystal belongs to the monoclinic space group C2. The crystal diffracted to 1.8 A resolution when analysed at 100 K using a rotating-anode X-ray generator.
