RESUMO
The 19 kDa protein (KAZ) of Oplophorus luciferase is a catalytic component, that oxidizes coelenterazine (a luciferin) with molecular oxygen to emit light. The crystal structure of the mutated 19 kDa protein (nanoKAZ) was determined at 1.71 Å resolution. The structure consists of 11 antiparallel ß-strands forming a ß-barrel that is capped by 4 short α-helices. The structure of nanoKAZ is similar to those of fatty acid-binding proteins (FABPs), even though the amino acid sequence similarity was very low between them. The coelenterazine-binding site and the catalytic site for the luminescence reaction might be in a central cavity of the ß-barrel structure.
Assuntos
Proteínas de Artrópodes/química , Proteínas de Artrópodes/ultraestrutura , Crustáceos/enzimologia , Imidazóis/química , Luciferases/química , Luciferases/ultraestrutura , Pirazinas/química , Sequência de Aminoácidos , Animais , Sítios de Ligação , Catálise , Simulação por Computador , Medições Luminescentes/métodos , Proteínas Luminescentes/química , Proteínas Luminescentes/uso terapêutico , Modelos Químicos , Modelos Moleculares , Dados de Sequência Molecular , Mutação , Ligação Proteica , Conformação Proteica , Estrutura Terciária de ProteínaRESUMO
Functional expression and spectroscopic analysis of luciferases from Lampyris turkestanicus and Photinus pyralis were carried out. cDNA encoding L. turkestanicus luciferase was isolated by reverse transcription-polymerase chain reaction, cloned, and functionally expressed in Escherichia coli. The luciferases were purified to homogeneity using Ni-nitrilotriacetic acid Sepharose, and kinetic properties of luciferase from L. turkestanicus were compared with that from P. pyralis. Amino acid differences in its primary structures in relation to P. pyralis luciferase brought about changes in the kinetic properties of the enzyme as evidenced by substantial lowering of Km for ATP, increased light decay time, and decreased thermostability. Luciferase from L. turkestanicus was used to carry out Michaelis-Menten kinetics with a Km of 95.5 muM for ATP and 20 muM for luciferin. Maximum activity was recorded at pH 8.5, so it might be a suitable reporter for microbial screening at alkaline pH. Tryptophan fluorescence for P. pyralis luciferase was higher than L. turkestanicus luciferase. Substitution of some residues in L. turkestanicus luciferase appears to change the kinetic properties by inducing a substantial tertiary structural change, without a large effect on secondary structural elements, as revealed by intrinsic and extrinsic fluorescence, Fourier transform infrared spectroscopy, and near-ultraviolet circular dichroism spectra.