scholarly journals The conserved cis-Pro39 residue plays a crucial role in the proper positioning of the catalytic base Asp38 in ketosteroid isomerase from Comamonas testosteroni

2003 ◽  
Vol 375 (2) ◽  
pp. 297-305 ◽  
Author(s):  
Gyu Hyun NAM ◽  
Sun-Shin CHA ◽  
Young Sung YUN ◽  
Yun Hee OH ◽  
Bee Hak HONG ◽  
...  
Keyword(s):  
Free Energy ◽  
Active Site ◽  
Crucial Role ◽  
Structural Integrity ◽  
Comamonas Testosteroni ◽  
Ketosteroid Isomerase ◽  
Free Energy Of Activation ◽  
Structural Rigidity ◽  
Diffusion Controlled

KSI (ketosteroid isomerase) from Comamonas testosteroni is a homodimeric enzyme that catalyses the allylic isomerization of Δ5-3-ketosteroids to their conjugated Δ4-isomers at a reaction rate equivalent to the diffusion-controlled limit. Based on the structural analysis of KSI at a high resolution, the conserved cis-Pro39 residue was proposed to be involved in the proper positioning of Asp38, a critical catalytic residue, since the residue was found not only to be structurally associated with Asp38, but also to confer a structural rigidity on the local active-site geometry consisting of Asp38, Pro39, Val40, Gly41 and Ser42 at the flexible loop between β-strands B1 and B2. In order to investigate the structural role of the conserved cis-Pro39 residue near the active site of KSI, Pro39 was replaced with alanine or glycine. The free energy of activation for the P39A and P39G mutants increased by 10.5 and 16.7 kJ/mol (2.5 and 4.0 kcal/mol) respectively, while ΔGUH2O (the free-energy change for unfolding in the absence of urea at 25.00±0.02 °C) decreased by 31.0 and 35.6 kJ/mol (7.4 and 8.5 kcal/mol) respectively, compared with the wild-type enzyme. The crystal structure of the P39A mutant in complex with d-equilenin [d-1,3,5(10),6,8-estrapentaen-3-ol-17-one], a reaction intermediate analogue, determined at 2.3 Å (0.23 nm) resolution revealed that the P39A mutation significantly disrupted the proper orientations of both d-equilenin and Asp38, as well as the local active-site geometry near Asp38, which resulted in substantial decreases in the activity and stability of KSI. Upon binding 1-anilinonaphthalene-8-sulphonic acid, the fluorescence intensities of the P39A and P39G mutants were increased drastically, with maximum wavelengths blue-shifted upon binding, indicating that the mutations might alter the hydrophobic active site of KSI. Taken together, our results demonstrate that the conserved cis-Pro39 residue plays a crucial role in the proper positioning of the critical catalytic base Asp38 and in the structural integrity of the active site in KSI.

SOME THEORETICAL ASPECTS OF ELECTRON-TRANSFER PROCESSES IN AQUEOUS SOLUTION

1959 ◽  
Vol 37 (1) ◽  
pp. 138-147 ◽  
Author(s):  
Keith J. Laidler
Keyword(s):  
Aqueous Solution ◽  
Electron Transfer ◽  
Free Energy ◽  
Energy Of Activation ◽  
Theoretical Treatment ◽  
Free Energy Of Activation ◽  
Diffusion Controlled ◽  
Entropy Of Activation ◽  
Pass Through ◽  
Electron Transfer Processes

A theoretical treatment has been developed for the rates of electron-transfer reactions in aqueous solution, with particular reference to the ferric–ferrous system. The reactions are considered to be diffusion-controlled processes, the approach of the ions being hindered by the electrostatic repulsion between them. Calculations have been made of the free energy of the diffusion process and for the repulsion, account being taken of the variation in dielectric constant with the electric field. The form of the potential-energy barrier between the ions is calculated for various separations, and the transmission coefficient calculated using the quantum-mechanical expression corresponding to a rectangular barrier. The total free energy of activation for the reaction, which is the sum of the contributions due to diffusion, repulsion, and tunnelling, is found to pass through a minimum at a separation of about 4 Å. The calculated free energy of activation for the reaction is 15.4 kcal, in good agreement with the experimental value of 16.8 kcal. The energy and entropy of activation for the reaction are also briefly discussed.

scholarly journals Role of the Active Site Guanine in theglmSRibozyme Self-Cleavage Mechanism: Quantum Mechanical/Molecular Mechanical Free Energy Simulations

2015 ◽  
Vol 137 (2) ◽  
pp. 784-798 ◽  
Author(s):  
Sixue Zhang ◽  
Abir Ganguly ◽  
Puja Goyal ◽  
Jamie L. Bingaman ◽  
Philip C. Bevilacqua ◽  
...  
Keyword(s):  
Free Energy ◽  
Active Site ◽  
Quantum Mechanical ◽  
Energy Simulations

Glutamic acid-65 is an essential residue for catalysis in Proteus mirabilis glutathione S-transferase B1-1

2002 ◽  
Vol 363 (1) ◽  
pp. 189-193 ◽  
Author(s):  
Nerino ALLOCATI ◽  
Michele MASULLI ◽  
Enrico CASALONE ◽  
Silvia SANTUCCI ◽  
Bartolo FAVALORO ◽  
...  
Keyword(s):  
Proteus Mirabilis ◽  
Active Site ◽  
Structural Integrity ◽  
Catalytic Efficiency ◽  
Site Directed Mutagenesis ◽  
Amino Acid Residues ◽  
Cd Spectra ◽  
Glutathione S Transferase ◽  
Terminal Amino

The functional role of three conserved amino acid residues in Proteus mirabilis glutathione S-transferase B1-1 (PmGST B1-1) has been investigated by site-directed mutagenesis. Crystallographic analyses indicated that Glu65, Ser103 and Glu104 are in hydrogen-bonding distance of the N-terminal amino group of the γ-glutamyl moiety of the co-substrate, GSH. Glu65 was mutated to either aspartic acid or leucine, and Ser103 and Glu104 were both mutated to alanine. Glu65 mutants (Glu65→Asp and Glu65→Leu) lost all enzyme activity, and a drastic decrease in catalytic efficiency was observed for Ser103→Ala and Glu104→Ala mutants toward both 1-chloro-2,4-dinitrobenzene and GSH. On the other hand, all mutants displayed similar intrinsic fluorescence, CD spectra and thermal stability, indicating that the mutations did not affect the structural integrity of the enzyme. Taken together, these results indicate that Ser103 and Glu104 are significantly involved in the interaction with GSH at the active site of PmGST B1-1, whereas Glu65 is crucial for catalysis.

scholarly journals Analyzing the catalytic role of active site residues in the Fe-type nitrile hydratase from Comamonas testosteroni Ni1

2015 ◽  
Vol 20 (5) ◽  
pp. 885-894 ◽  
Author(s):  
Salette Martinez ◽  
Rui Wu ◽  
Karoline Krzywda ◽  
Veronika Opalka ◽  
Hei Chan ◽  
...  
Keyword(s):  
Active Site ◽  
Nitrile Hydratase ◽  
Comamonas Testosteroni ◽  
Active Site Residues ◽  
Catalytic Role

scholarly journals EB1 Is Essential during Drosophila Development and Plays a Crucial Role in the Integrity of Chordotonal Mechanosensory Organs

2005 ◽  
Vol 16 (2) ◽  
pp. 891-901 ◽  
Author(s):  
Sarah L. Elliott ◽  
C. Fiona Cullen ◽  
Nicola Wrobel ◽  
Maurice J. Kernan ◽  
Hiroyuki Ohkura
Keyword(s):  
Cell Division ◽  
Crucial Role ◽  
Structural Integrity ◽  
Cultured Cells ◽  
Structure And Function ◽  
Cell Cortex ◽  
Microtubule Organization ◽  
Electrophysiological Measurements ◽  
And Function

EB1 is a conserved microtubule plus end tracking protein considered to play crucial roles in microtubule organization and the interaction of microtubules with the cell cortex. Despite intense studies carried out in yeast and cultured cells, the role of EB1 in multicellular systems remains to be elucidated. Here, we describe the first genetic study of EB1 in developing animals. We show that one of the multiple Drosophila EB1 homologues, DmEB1, is ubiquitously expressed and has essential functions during development. Hypomorphic DmEB1 mutants show neuromuscular defects, including flightlessness and uncoordinated movement, without any general cell division defects. These defects can be partly explained by the malfunction of the chordotonal mechanosensory organs. In fact, electrophysiological measurements indicated that the auditory chordotonal organs show a reduced response to sound stimuli. The internal organization of the chordotonal organs also is affected in the mutant. Consistently, DmEB1 is enriched in those regions important for the structure and function of the organs. Therefore, DmEB1 plays a crucial role in the functional and structural integrity of the chordotonal mechanosensory organs in Drosophila.

scholarly journals Proline 36 of the Factor XIII Activation Peptide Plays a Crucial Role in Substrate Recognition and Zymogen Activation

2018 ◽  
Vol 118 (12) ◽  
pp. 2037-2045 ◽  
Author(s):  
Bojun Li ◽  
Ramya Billur ◽  
Muriel Maurer ◽  
Hans Kohler ◽  
Pascale Raddatz Müller ◽  
...  
Keyword(s):  
Active Site ◽  
Crucial Role ◽  
Factor Xiii ◽  
Chinese Hamster Ovary Cells ◽  
Chinese Hamster ◽  
Nuclear Magnetic Resonance Analysis ◽  
Zymogen Activation ◽  
Proteolytic Activation ◽  
Activation Peptide

AbstractThe activation peptide of blood coagulation factor XIII (AP-FXIII) has important functions in stabilizing the FXIII-A2 dimer and regulating FXIII activation. Contributions of many of its 37 amino acids to these functions have been described. However, the role of proline 36, which is adjacent to the thrombin cleavage site at Arg37, has not yet been studied in detail. We approached this question when we came across a patient with congenital FXIII deficiency in whom we detected a novel Pro36Ser mutation. We expressed the mutant FXIII-A Pro36Ser protein in Chinese hamster ovary cells and found that this mutation does not influence FXIII-A expression but significantly inhibits proteolytic activation by thrombin. The enzymatic transglutaminase activity is not affected as it can be induced in the presence of high Ca2+ concentrations. We performed nuclear magnetic resonance analysis to investigate AP-FXIII–thrombin interactions, which showed that the mutant Ser36 peptide binds less well to the thrombin surface than the native Pro36 peptide. The Arg37 at the P1 position still makes strong interactions with the active site cleft but the P4–P2 residues (34VVS36) appear to be less well positioned to contact the neighbouring thrombin active site region. In conclusion, we have characterized a novel mutation in AP-FXIII representing only the fourth case of the rare FXIII-A type II deficiency. This case served as a perfect in vivo model to shed light on the crucial role of Pro36 in the proteolytic activation of FXIII-A. Our results contribute to the understanding of structure–function relationship in FXIII.

Sign in / Sign up

Export Citation Format

Share Document