title: Tyrosine phenol-lyase and tryptophan indole-lyase encapsulated in wet nanoporous silica gels: Selective stabilization of tertiary conformations.
abstract: The pyridoxal 5'-phosphate-dependent enzymes tyrosine phenol-lyase and tryptophan indole-lyase were encapsulated in wet nanoporous silica gels, a powerful method to selectively stabilize tertiary and quaternary protein conformations and to develop bioreactors and biosensors. A comparison of the enzyme reactivity in silica gels and in solution was carried out by determining equilibrium and kinetic parameters, exploiting the distinct spectral properties of catalytic intermediates and reaction products. The encapsulated enzymes exhibit altered distributions of ketoenamine and enolimine tautomers, increased values of inhibitors dissociation constants, slow attaining of steady-state in the presence of substrate and substrate analogs, modified steady-state distribution of catalytic intermediates, and a sixfold-eightfold decrease of specific activities. This behavior can be rationalized by a reduced conformational flexibility for the encapsulated enzymes and a selective stabilization of either the open (inactive) or the closed (active) form of the enzymes. Despite very similar structures and catalytic mechanisms, the influence of encapsulation is more pronounced for tyrosine phenol-lyase than tryptophan indole-lyase. This finding indicates that subtle structural and dynamic differences can lead to distinct interactions of the protein with the gel matrix.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Parma, Via Parco delle Scienze 23/A, 43100 Parma, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Pioselli
authors.forename: Stefano
authors.initials: S
authors.lastname: Bettati
authors.forename: Tatyana V
authors.initials: TV
authors.lastname: Demidkina
authors.forename: Lyudmila N
authors.initials: LN
authors.lastname: Zakomirdina
authors.forename: Robert S
authors.initials: RS
authors.lastname: Phillips
authors.forename: Andrea
authors.initials: A
authors.lastname: Mozzarelli
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry*; D002384:Catalysis; D016971:Citrobacter freundii / Q000201:enzymology*; D004795:Enzyme Stability; D004800:Enzymes, Immobilized / Q000737:chemistry; D007700:Kinetics; D011487:Protein Conformation; D011514:Proteus vulgaris / Q000201:enzymology*; D058428:Silica Gel; D012822:Silicon Dioxide / Q000737:chemistry*; D013379:Substrate Specificity; D014368:Tryptophanase / Q000737:chemistry*; D014447:Tyrosine Phenol-Lyase / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D004800:Enzymes, Immobilized; D058428:Silica Gel; D012822:Silicon Dioxide; D014368:Tryptophanase; D014447:Tyrosine Phenol-Lyase