The isolated proteolytic domain of Escherichia coli ATP-dependent protease Lon exhibits the peptidase activity

AbstractSelective protein degradation is an energy-dependent process performed by high-molecular-weight proteases. The activity of proteolytic components of these enzymes is coupled to the ATPase activity of their regulatory subunits or domains. Here, we obtained the proteolytic domain of Escherichia coli protease Lon by cloning the corresponding fragment of the lon gene in pGEX-KG, expression of the hybrid protein, and isolation of the proteolytic domain after hydrolysis of the hybrid protein with thrombin. The isolated proteolytic domain exhibited almost no activity toward protein substrates (casein) but hydrolyzed peptide substrates (melittin), thereby confirming the importance of the ATPase component for protein hydrolysis. Protease Lon and its proteolytic domain differed in the efficiency and specificity of melittin hydrolysis

Probing the Role of a Conserved Phenylalanine in the Active Site of Thiocyanate Dehydrogenase

Copper-containing enzymes catalyze a broad spectrum of redox reactions. Thiocyanate dehydrogenase (TcDH) from Thioalkalivibrio paradoxus Arh1 enables the bacterium to use thiocyanate as a unique source of energy and nitrogen. Oxidation of thiocyanate takes place in the trinuclear copper center of TcDH with peculiar organization. Despite the TcDH crystal structure being established, a role of some residues in the enzyme active site has yet to be obscured. F436 residue is located in the enzyme active site and conserved among a number of TcDH homologs, however, its role in the copper center formation or the catalytic process is still not clear. To address this question, a mutant form of the enzyme with F436Q substitution (TcDHF436Q) was obtained, biochemically characterized, and its crystal structure was determined. The TcDHF436Q had an unaltered protein fold but did not possess enzymatic activity, whereas it contained all three copper ions, according to ICP-MS data. The structural data showed that the F436Q substitution resulted in a disturbance of hydrophobic interactions within the active site crucial for a correct transition between open/closed forms of the enzyme–substrate channel. Thus, we demonstrated that F436 does not participate in copper ion binding, but rather possesses a structural role in the TcDH active site

Probing the Role of a Conserved Phenylalanine in the Active Site of Thiocyanate Dehydrogenase

Copper-containing enzymes catalyze a broad spectrum of redox reactions. Thiocyanate dehydrogenase (TcDH) from Thioalkalivibrio paradoxus Arh1 enables the bacterium to use thiocyanate as a unique source of energy and nitrogen. Oxidation of thiocyanate takes place in the trinuclear copper center of TcDH with peculiar organization. Despite the TcDH crystal structure being established, a role of some residues in the enzyme active site has yet to be obscured. F436 residue is located in the enzyme active site and conserved among a number of TcDH homologs, however, its role in the copper center formation or the catalytic process is still not clear. To address this question, a mutant form of the enzyme with F436Q substitution (TcDHF436Q) was obtained, biochemically characterized, and its crystal structure was determined. The TcDHF436Q had an unaltered protein fold but did not possess enzymatic activity, whereas it contained all three copper ions, according to ICP-MS data. The structural data showed that the F436Q substitution resulted in a disturbance of hydrophobic interactions within the active site crucial for a correct transition between open/closed forms of the enzyme–substrate channel. Thus, we demonstrated that F436 does not participate in copper ion binding, but rather possesses a structural role in the TcDH active site

Unusual Cytochrome c552 from Thioalkalivibrio paradoxus: Solution NMR Structure and Interaction with Thiocyanate Dehydrogenase

The search of a putative physiological electron acceptor for thiocyanate dehydrogenase (TcDH) newly discovered in the thiocyanate-oxidizing bacteria Thioalkalivibrio paradoxus revealed an unusually large, single-heme cytochrome c (CytC552), which was co-purified with TcDH from the periplasm. Recombinant CytC552, produced in Escherichia coli as a mature protein without a signal peptide, has spectral properties similar to the endogenous protein and serves as an in vitro electron acceptor in the TcDH-catalyzed reaction. The CytC552 structure determined by NMR spectroscopy reveals significant differences compared to those of the typical class I bacterial cytochromes c: a high solvent accessible surface area for the heme group and so-called “intrinsically disordered” nature of the histidine-rich N- and C-terminal regions. Comparison of the signal splitting in the heteronuclear NMR spectra of oxidized, reduced, and TcDH-bound CytC552 reveals the heme axial methionine fluxionality. The TcDH binding site on the CytC552 surface was mapped using NMR chemical shift perturbations. Putative TcDH-CytC552 complexes were reconstructed by the information-driven docking approach and used for the analysis of effective electron transfer pathways. The best pathway includes the electron hopping through His528 and Tyr164 of TcDH, and His83 of CytC552 to the heme group in accordance with pH-dependence of TcDH activity with CytC552

Novel Extracellular Electron Transfer Channels in a Gram-Positive Thermophilic Bacterium

publishedVersio

Unusual Cytochrome c552 from Thioalkalivibrio paradoxus: Solution NMR Structure and Interaction with Thiocyanate Dehydrogenase

The search of a putative physiological electron acceptor for thiocyanate dehydrogenase (TcDH) newly discovered in the thiocyanate-oxidizing bacteria Thioalkalivibrio paradoxus revealed an unusually large, single-heme cytochrome c (CytC552), which was co-purified with TcDH from the periplasm. Recombinant CytC552, produced in Escherichia coli as a mature protein without a signal peptide, has spectral properties similar to the endogenous protein and serves as an in vitro electron acceptor in the TcDH-catalyzed reaction. The CytC552 structure determined by NMR spectroscopy reveals significant differences compared to those of the typical class I bacterial cytochromes c: a high solvent accessible surface area for the heme group and so-called “intrinsically disordered” nature of the histidine-rich N- and C-terminal regions. Comparison of the signal splitting in the heteronuclear NMR spectra of oxidized, reduced, and TcDH-bound CytC552 reveals the heme axial methionine fluxionality. The TcDH binding site on the CytC552 surface was mapped using NMR chemical shift perturbations. Putative TcDH-CytC552 complexes were reconstructed by the information-driven docking approach and used for the analysis of effective electron transfer pathways. The best pathway includes the electron hopping through His528 and Tyr164 of TcDH, and His83 of CytC552 to the heme group in accordance with pH-dependence of TcDH activity with CytC552