A Dynamic Substrate is Required for MhuD-catalyzed Degradation of Heme to Mycobilin

2020 ◽  
Author(s):  
Biswash Thakuri ◽  
Bruce O'Rourke ◽  
Amanda Graves ◽  
Matthew Liptak
Keyword(s):  
Dynamic Equilibrium ◽  
Ionization Mass ◽  
Esi Ms ◽  
Enzymatic Mechanism ◽  
Single Turnover ◽  
Rate Limiting Step ◽  
Planar Substrate ◽  
Out Of Plane ◽  
Substrate Conformation ◽  
Rate Limiting

The non-canoncial heme oxygenase MhuD from <i>Mycobacterium tuberculosis</i> binds a heme substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between heme substrate dynamics and MhuD-catalyzed heme degradation resulting in a revised enzymatic mechanism. UV/Vis absorption (Abs) and electrospray ionization mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favoring population of the ruffled heme conformation changed the rate-limiting step of the reaction resulting in a measurable build-up of the monooxygenated meso-hydroxyheme intermediate. In addition, UV/Vis Abs and ESI-MS data for a second-sphere variant that favored the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an alpha-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of heme monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyheme dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled haem conformation supports rapid heme monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered heme monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyheme. Altogether, these data yielded a revised enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into heme yielding mycobilin.<br>

A Dynamic Substrate is Required for MhuD-catalyzed Degradation of Heme to Mycobilin

2021 ◽  
Author(s):  
Biswash Thakuri ◽  
Bruce O'Rourke ◽  
Amanda Graves ◽  
Matthew Liptak
Keyword(s):  
Dynamic Equilibrium ◽  
Ionization Mass ◽  
Esi Ms ◽  
Enzymatic Mechanism ◽  
Single Turnover ◽  
Rate Limiting Step ◽  
Planar Substrate ◽  
Out Of Plane ◽  
Substrate Conformation ◽  
Rate Limiting

The non-canoncial heme oxygenase MhuD from <i>Mycobacterium tuberculosis</i> binds a heme substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between heme substrate dynamics and MhuD-catalyzed heme degradation resulting in a refined enzymatic mechanism. UV/Vis absorption (Abs) and electrospray ionization mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favoring population of the ruffled heme conformation changed the rate-limiting step of the reaction resulting in a measurable build-up of the monooxygenated meso-hydroxyheme intermediate. In addition, UV/Vis Abs and ESI-MS data for a second-sphere variant that favored the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an alpha-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of heme monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyheme dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled haem conformation supports rapid heme monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered heme monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyheme. Altogether, these data yielded a refined enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into heme yielding mycobilin.<br>

scholarly journals A Dynamic Substrate is Required for MhuD-catalyzed Degradation of Heme to Mycobilin

2020 ◽  
Author(s):  
Biswash Thakuri ◽  
Bruce O'Rourke ◽  
Amanda Graves ◽  
Matthew Liptak
Keyword(s):  
Dynamic Equilibrium ◽  
Ionization Mass ◽  
Esi Ms ◽  
Enzymatic Mechanism ◽  
Single Turnover ◽  
Rate Limiting Step ◽  
Planar Substrate ◽  
Out Of Plane ◽  
Substrate Conformation ◽  
Rate Limiting

The non-canoncial heme oxygenase MhuD from <i>Mycobacterium tuberculosis</i> binds a heme substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between heme substrate dynamics and MhuD-catalyzed heme degradation resulting in a revised enzymatic mechanism. UV/Vis absorption (Abs) and electrospray ionization mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favoring population of the ruffled heme conformation changed the rate-limiting step of the reaction resulting in a measurable build-up of the monooxygenated meso-hydroxyheme intermediate. In addition, UV/Vis Abs and ESI-MS data for a second-sphere variant that favored the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an alpha-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of heme monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyheme dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled haem conformation supports rapid heme monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered heme monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyheme. Altogether, these data yielded a revised enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into heme yielding mycobilin.<br>

scholarly journals A Dynamic Substrate is Required for MhuD-catalyzed Degradation of Heme to Mycobilin

2021 ◽  
Author(s):  
Biswash Thakuri ◽  
Bruce O'Rourke ◽  
Amanda Graves ◽  
Matthew Liptak
Keyword(s):  
Dynamic Equilibrium ◽  
Ionization Mass ◽  
Esi Ms ◽  
Enzymatic Mechanism ◽  
Single Turnover ◽  
Rate Limiting Step ◽  
Planar Substrate ◽  
Out Of Plane ◽  
Substrate Conformation ◽  
Rate Limiting

The non-canoncial heme oxygenase MhuD from <i>Mycobacterium tuberculosis</i> binds a heme substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between heme substrate dynamics and MhuD-catalyzed heme degradation resulting in a refined enzymatic mechanism. UV/Vis absorption (Abs) and electrospray ionization mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favoring population of the ruffled heme conformation changed the rate-limiting step of the reaction resulting in a measurable build-up of the monooxygenated meso-hydroxyheme intermediate. In addition, UV/Vis Abs and ESI-MS data for a second-sphere variant that favored the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an alpha-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of heme monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyheme dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled haem conformation supports rapid heme monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered heme monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyheme. Altogether, these data yielded a refined enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into heme yielding mycobilin.<br>

scholarly journals A Dynamic Substrate is Required for MhuD-catalysed Degradation of Haem to Mycobilin

2020 ◽  
Author(s):  
Biswash Thakuri ◽  
Bruce O'Rourke ◽  
Amanda Graves ◽  
Matthew Liptak
Keyword(s):  
Dynamic Equilibrium ◽  
Esi Ms ◽  
Enzymatic Mechanism ◽  
Single Turnover ◽  
Rate Limiting Step ◽  
Planar Substrate ◽  
Ionisation Mass Spectrometry ◽  
Out Of Plane ◽  
Haem Oxygenase ◽  
Substrate Conformation

The non-canoncial haem oxygenase MhuD from <i>Mycobacterium tuberculosis</i> binds a haem substrate that adopts a dynamic equilibrium between planar and out-of-plane ruffled conformations. MhuD degrades this substrate to an unusual mycobilin product via successive monooxygenation and dioxygenation reactions. This article establishes a causal relationship between haem substrate dynamics and MhuD-catalysed haem degradation resulting in a revised enzymatic mechanism. UV/Vis absorption (Abs) and electrospray ionisation mass spectrometry (ESI-MS) data demonstrated that a second-sphere substitution favouring population of the ruffled haem conformation changed the rate-limiting step of the reaction resulting in a measurable build-up of the monooxygenated meso-hydroxyhaem intermediate. In addition, UV/Vis Abs and ESI-MS data for a second-sphere variant that favoured the planar substrate conformation showed that this change altered the enzymatic mechanism resulting in an alpha-biliverdin product. Single-turnover kinetic analyses for three MhuD variants revealed that the rate of haem monooxygenation depends upon the population of the ruffled substrate conformation. These kinetic analyses also revealed that the rate of meso-hydroxyhaem dioxygenation by MhuD depends upon the population of the planar substrate conformation. Thus, the ruffled haem conformation supports rapid haem monooxygenation by MhuD, but further oxygenation to the mycobilin product is inhibited. In contrast, the planar substrate conformation exhibits altered haem monooxygenation regiospecificity followed by rapid oxygenation of meso-hydroxyhaem. Altogether, these data yielded a revised enzymatic mechanism for MhuD where access to both substrate conformations is needed for rapid incorporation of three oxygen atoms into haem yielding mycobilin.<br>

scholarly journals Ruffling is Essential for Staphylococcus aureus IsdG-catalyzed Degradation of Heme to Staphylobilin

2021 ◽  
Author(s):  
Ariel Schuelke-Sanchez ◽  
Amanda Cornetta ◽  
Taylor Kocian ◽  
Matthew Conger ◽  
Matthew Liptak
Keyword(s):  
Staphylococcus Aureus ◽  
Dynamic Equilibrium ◽  
Iron Acquisition ◽  
Protein Secondary Structure ◽  
Heme Iron ◽  
Ionization Mass ◽  
Heme Oxygenases ◽  
Planar Substrate ◽  
Rearrangement Mechanism ◽  
Substrate Conformation

Non-canonical heme oxygenases are enzymes that degrade heme to non-biliverdin products within bacterial heme iron acquisition pathways. These enzymes all contain a conserved second-sphere Trp residue that is essential for enzymatic turnover. Previous studies have revealed several important roles for the conserved second-sphere Trp in Staphylococcus aureus IsdG, S. aureus IsdI, and Mycobacterium tuberculosis MhuD. However, a general model for the geometric, electronic, and functional role of the second-sphere Trp had not been deduced prior to this work. Here, UV/Vis absorption (Abs) and circular dichroism (CD) spectroscopies were employed to show that the W67F variant of IsdG perturbs the heme substrate conformation without altering the protein secondary structure. In general, it can now be stated that a dynamic equilibrium between “planar” and “ruffled” substrate conformations exists within non-canonical heme oxygenases, and that the second-sphere Trp favors population of the “ruffled” substrate conformation. 1H nuclear magnetic resonance and magnetic CD spectroscopies were used to characterize the electronic structures of IsdG and IsdI variants with different substrate conformational distributions. These data revealed that the “ruffled” substrate conformation promotes partial porphyrin-to-iron electron transfer, which makes the meso carbons of the porphyrin ring susceptible to radical attack. Finally, UV/Vis Abs spectroscopy was utilized to quantify the enzymatic rates, and electrospray ionization mass spectrometry was used to identify the product distributions, for variants of IsdG with altered substrate conformational distributions. In general, the rate of heme oxygenation by non-canonical heme oxygenases depends upon the population of the “ruffled” substrate conformation. Also, the production of staphylobilin or mycobilin by these enzymes is correlated with the population of the “ruffled” substrate conformation, since variants that favor population of the “planar” substrate conformation yield significant amounts of biliverdin. These data can be understood within the framework of a concerted rearrangement mechanism for the monooxygenation of heme to meso-hydroxyheme by non-canonical heme oxygenases. However, the mechanisms of IsdG/IsdI and MhuD must diverge following this intermediate in order to generate distinct staphylobilin and mycobilin products, respectively.

scholarly journals Secondary organic material formed by methylglyoxal in aqueous aerosol mimics

2010 ◽  
Vol 10 (3) ◽  
pp. 997-1016 ◽  
Author(s):  
N. Sareen ◽  
A. N. Schwier ◽  
E. L. Shapiro ◽  
D. Mitroo ◽  
V. F. McNeill
Keyword(s):  
Organic Material ◽  
Aldol Condensation ◽  
Bimolecular Reaction ◽  
Ionization Mass ◽  
Aerosol Formation ◽  
Hydronium Ion ◽  
Rate Limiting Step ◽  
Tropospheric Aerosol ◽  
Heterogeneous Processes ◽  
Rate Limiting

Abstract. We show that methylglyoxal forms light-absorbing secondary organic material in aqueous ammonium sulfate and ammonium nitrate solutions mimicking tropospheric aerosol particles. The kinetics were characterized using UV-Vis spectrophotometry. The results suggest that the bimolecular reaction of methylglyoxal with an ammonium or hydronium ion is the rate-limiting step for the formation of light-absorbing species, with kNH4+II=5×10−6 M−1 min−1 and kH3O+II≤10−3 M−1 min−1. Evidence of aldol condensation products and oligomeric species up to 759 amu was found using chemical ionization mass spectrometry with a volatilization flow tube inlet (Aerosol-CIMS). Tentative identifications of carbon-nitrogen species and a sulfur-containing compound were also made using Aerosol-CIMS. Aqueous solutions of methylglyoxal, with and without inorganic salts, exhibit significant surface tension depression. These observations add to the growing body of evidence that dicarbonyl compounds may form secondary organic material in the aerosol aqueous phase, and that secondary organic aerosol formation via heterogeneous processes may affect seed aerosol properties.

scholarly journals Bacterial Sec Protein Transport Is Rate-limited by Precursor Length: A Single Turnover Study

2009 ◽  
Vol 20 (19) ◽  
pp. 4256-4266 ◽  
Author(s):  
Fu-Cheng Liang ◽  
Umesh K. Bageshwar ◽  
Siegfried M. Musser
Keyword(s):  
Protein Transport ◽  
Atp Hydrolysis ◽  
Membrane Vesicles ◽  
Single Turnover ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Precursor Proteins ◽  
Inverted Membrane Vesicles ◽  
Rate Limiting

An in vitro real-time single turnover assay for the Escherichia coli Sec transport system was developed based on fluorescence dequenching. This assay corrects for the fluorescence quenching that occurs when fluorescent precursor proteins are transported into the lumen of inverted membrane vesicles. We found that 1) the kinetics were well fit by a single exponential, even when the ATP concentration was rate-limiting; 2) ATP hydrolysis occurred during most of the observable reaction period; and 3) longer precursor proteins transported more slowly than shorter precursor proteins. If protein transport through the SecYEG pore is the rate-limiting step of transport, which seems likely, these conclusions argue against a model in which precursor movement through the SecYEG translocon is mechanically driven by a series of rate-limiting, discrete translocation steps that result from conformational cycling of the SecA ATPase. Instead, we propose that precursor movement results predominantly from Brownian motion and that the SecA ATPase regulates pore accessibility.

Product Release is Not the Rate-Limiting Step during Cytochalasin B-Induced ATPase Activity of Monomeric Actin

1991 ◽  
Vol 46 (1-2) ◽  
pp. 139-144 ◽  
Author(s):  
Peter Dancker ◽  
Lore Hess ◽  
Karl Ritter
Keyword(s):  
Steady State ◽  
Atpase Activity ◽  
Rate Constant ◽  
Cytochalasin B ◽  
Single Turnover ◽  
Rate Limiting Step ◽  
Hydrolysis Products ◽  
Limiting Step ◽  
Rate Limiting ◽  
Hydrolysis Of

Abstract Under conditions where cytochalasin B induces ATPase activity of monomeric actin (0.3 mᴍ MgCl2, 1 mᴍ EGTA , 30 (μᴍ cytochalasin B, 1 mᴍ ATP) the rate constant of the ex­change of actin-bound ε-ATP for free ATP is about 4 -6 times faster than steady state ATPase activity. When a stoichiometric ATP -actin complex is extracted with PCA (single turnover ex­periment) the apparent rate constant of Pi generation is not faster than steady state ATPase activity. -The experiments suggest that the hydrolysis of actin-bound ATP and not the subse­quent release of hydrolysis products is rate-limiting during cytochalasin-induced ATPase activi­ty of actin.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Sign in / Sign up

Export Citation Format

Share Document