The extreme thermostable pyrophosphatase from Sulfolobus acidocaldarius: enzymatic and comparative biophysical characterization.
Recombinant pyrophosphatase from the hyperthermophilic archaebacterium Sulfolobus acidocaldarius (S-PPase) has been heterologously expressed in Escherichia coli and could be purified in large quantities. S-PPase, previously described as a tetrameric enzyme, was shown to be a homohexameric protein that had catalytic activity with Mg2+ > Zn2+ > Co2+ >> Mn2+ >> Ni2+, Ca2+. CD and FTIR spectra demonstrate a similar overall fold for S-PPase and PPases from E. coli (E-PPase) and Thermus thermophilus (T-PPase). The relative proportions of secondary structure elements in S-PPase are close to those of a previously proposed model. S-PPase is extremely heat resistant. Even at 95 degrees C the half-life of catalytic activity is 2.5 h, which is dramatically increased in the presence of divalent cations. More than one Mg2+ per monomer is needed for catalysis, but no more than one Mg2+ per monomer is sufficient for thermal stabilization. The Tm values for S-PPase are 89 degrees C (+EDTA), 99 degrees C (+Mg2+), and >100 degrees C (+Mn2+), compared to 58 degrees C (+EDTA), 84 degrees C (+Mg2+), and 93 degrees C (+Mn2+) for E-PPase and 86 degrees C (+EDTA), 99 degrees C (+Mg2+), and 96 degrees C (+Mn2+) for T-PPase. The guanidium hydrochloride-induced unfolding follows an unknown mechanism with a biphasic kinetic and an unstable intermediate. Unfolding curves of the S-, E-, and T-PPase are independent of the method applied (CD spectroscopy and fluorescence) and show a sigmoidal and monophasic transition, indicating a change in global structure during unfolding, which can be described by a two-state process comprising dissociation and denaturation of the folded hexamer into six monomers. The respective DeltaGN-->D(25 degrees C) values of the three PPases vary from 220 to 290 kJ/mol for the overall process and are not significantly higher for the two thermophilic PPases. The stabilizing effect of Mg2+ DeltaDeltaG(25 degrees C) is 16 kJ/mol for E-PPase and 5.5-8 kJ/mol for S-PPase and T-PPase.
Institute of Biochemistry, Medical University of Lübeck, Ratzeburger Allee 160, Lübeck, D-23538, Germany.
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T
Hansen
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Urbanke
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Leppänen
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A
Goldman
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Brandenburg
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Schäfer
D001426:Bacterial Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D002942:Circular Dichroism; D011756:Diphosphates / Q000378:metabolism; D004795:Enzyme Stability / Q000502:physiology; D004926:Escherichia coli / Q000201:enzymology; D019791:Guanidine / Q000494:pharmacology; D006358:Hot Temperature; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011755:Pyrophosphatases / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared; D016945:Sulfolobus acidocaldarius / Q000201:enzymology*; D016963:Thermus thermophilus / Q000201:enzymology; D014461:Ultracentrifugation
D001426:Bacterial Proteins; D002413:Cations, Divalent; D011756:Diphosphates; D011994:Recombinant Proteins; D011755:Pyrophosphatases; D019791:Guanidine