6 research outputs found
Distinct conformational behaviors of four mammalian dualāflavin reductases (cytochrome P450 reductase, methionine synthase reductase, neuronal nitric oxide synthase, endothelial nitric oxide synthase) determine their unique catalytic profiles
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109651/1/febs13073.pd
Distinct Conformational Behaviors of Four Mammalian Dual-Flavin Reductases (Cytochrome P450 Reductase, Methionine Synthase Reductase, Neuronal Nitric Oxide Synthase, Endothelial Nitric Oxide Synthase) Determine Their Unique Catalytic Profiles
Multidomain enzymes often rely on large conformational motions to function. However, the conformational setpoints, rates of domain motions and relationships between these parameters and catalytic activity are not well understood. To address this, we determined and compared the conformational setpoints and the rates of conformational switching between closed unreactive and open reactive states in four mammalian diflavin NADPH oxidoreductases that catalyze important biological electron transfer reactions: cytochrome P450 reductase, methionine synthase reductase and endothelial and neuronal nitric oxide synthase. We used stopped-flow spectroscopy, single turnover methods and a kinetic model that relates electron flux through each enzyme to its conformational setpoint and its rates of conformational switching. The results show that the four flavoproteins, when fully-reduced, have a broad range of conformational setpoints (from 12% to 72% open state) and also vary 100-fold with respect to their rates of conformational switching between unreactive closed and reactive open states (cytochrome P450 reductase \u3e neuronal nitric oxide synthase \u3e methionine synthase reductase \u3e endothelial nitric oxide synthase). Furthermore, simulations of the kinetic model could explain how each flavoprotein can support its given rate of electron flux (cytochrome c reductase activity) based on its unique conformational setpoint and switching rates. The present study is the first to quantify these conformational parameters among the diflavin enzymes and suggests how the parameters might be manipulated to speed or slow biological electron flux
Context-dependent monoclonal antibodies against protein carbamidomethyl-cysteine.
Protein sulfhydryl residues participate in key structural and biochemical functions. Alterations in sulfhydryl status, regulated by either reversible redox reactions or by permanent covalent capping, may be challenging to identify. To advance the detection of protein sulfhydryl groups, we describe the production of new Rabbit monoclonal antibodies that react with carbamidomethyl-cysteine (CAM-cys), a product of iodoacetamide (IAM) labeling of protein sulfhydryl residues. These antibodies bind to proteins labeled with IAM (but not N-ethylmaleimide (NEM) or acrylamide) and identify multiple protein bands when applied to Western blots of cell lysates treated with IAM. The monoclonal antibodies label a subset of CAM-cys modified peptide sequences and purified proteins (human von Willebrand Factor (gene:vWF), Jagged 1 (gene:JAG1), Laminin subunit alpha 2 (gene:LAMA2), Thrombospondin-2 (gene:TSP2), and Collagen IV (gene:COL4)) but do not recognize specific proteins such as Bovine serum albumin (gene:BSA) and human Thrombospondin-1 (gene:TSP1), Biglycan (gene:BGN) and Decorin (gene:DCN). Scanning mutants of the peptide sequence used to generate the CAM-cys antibodies elucidated residues required for context dependent reactivity. In addition to recognition of in vitro labeled proteins, the antibodies were used to identify selected sulfhydryl-containing proteins from living cells that were pulse labeled with IAM. Further development of novel CAM-cys monoclonal antibodies in conjunction with other biochemical tools may complement current methods for sulfhydryl detection within specific proteins. Moreover, CAM-cys reactive reagents may be useful when there is a need to label subpopulations of proteins
Trans-Reduction of Cerebral Small Vessel Disease Proteins by Notch-Derived EGF-like Sequences
Cysteine oxidation states of extracellular proteins participate in functional regulation and in disease pathophysiology. In the most common inherited dementia, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), mutations in NOTCH3 that alter extracellular cysteine number have implicated NOTCH3 cysteine states as potential triggers of cerebral vascular smooth muscle cytopathology. In this report, we describe a novel property of the second EGF-like domain of NOTCH3: its capacity to alter the cysteine redox state of the NOTCH3 ectodomain. Synthetic peptides corresponding to this sequence (NOTCH3 N-terminal fragment 2, NTF2) readily reduce NOTCH3 N-terminal ectodomain polypeptides in a dose- and time-dependent fashion. Furthermore, NTF2 preferentially reduces regional domains of NOTCH3 with the highest intensity against EGF-like domains 12–15. This process requires cysteine residues of NTF2 and is also capable of targeting selected extracellular proteins that include TSP2 and CTSH. CADASIL mutations in NOTCH3 increase susceptibility to NTF2-facilitated reduction and to trans-reduction by NOTCH3 produced in cells. Moreover, NTF2 forms complexes with the NOTCH3 ectodomain, and cleaved NOTCH3 co-localizes with the NOTCH3 ectodomain in cerebral arteries of CADASIL patients. The potential for NTF2 to reduce vascular proteins and the enhanced preference for it to trans-reduce mutant NOTCH3 implicate a role for protein trans-reduction in cerebrovascular pathological states such as CADASIL
Role of the Proximal Cysteine Hydrogen Bonding Interaction in Cytochrome P450 2B4 Studied by Cryoreduction, Electron Paramagnetic Resonance, and ElectronNuclear Double Resonance Spectroscopy
Role of the Proximal Cysteine Hydrogen Bonding Interaction in Cytochrome P450 2B4 Studied by Cryoreduction, Electron Paramagnetic Resonance, and ElectronāNuclear Double Resonance Spectroscopy
Crystallographic studies have shown
that the F429H mutation of
cytochrome P450 2B4 introduces an H-bond between His429 and the proximal
thiolate ligand, Cys436, without altering the protein fold but sharply
decreases the enzymatic activity and stabilizes the oxyferrous P450
2B4 complex. To characterize the influence of this hydrogen bond on
the states of the catalytic cycle, we have used radiolytic cryoreduction
combined with electron paramagnetic resonance (EPR) and (electronānuclear
double resonance (ENDOR) spectroscopy to study and compare their characteristics
for wild-type (WT) P450 2B4 and the F429H mutant. (i) The addition
of an H-bond to the axial Cys436 thiolate significantly changes the
EPR signals of both low-spin and high-spin heme-ironĀ(III) and the
hyperfine couplings of the heme-pyrrole <sup>14</sup>N but has relatively
little effect on the <sup>1</sup>H ENDOR spectra of the water ligand
in the six-coordinate low-spin ferriheme state. These changes indicate
that the H-bond introduced between His and the proximal cysteine decreases
the extent of S ā Fe electron donation and weakens the FeĀ(III)āS
bond. (ii) The added H-bond changes the primary product of cryoreduction
of the FeĀ(II) enzyme, which is trapped in the conformation of the
parent FeĀ(II) state. In the wild-type enzyme, the added electron localizes
on the porphyrin, generating an <i>S</i> = <sup>3</sup>/<sub>2</sub> state with the anion radical exchange-coupled to the FeĀ(II).
In the mutant, it localizes on the iron, generating an <i>S</i> = <sup>1</sup>/<sub>2</sub> FeĀ(I) state. (iii) The additional H-bond
has little effect on <i>g</i> values and <sup>1</sup>Hā<sup>14</sup>N hyperfine couplings of the cryogenerated, ferric hydroperoxo
intermediate but noticeably slows its decay during cryoannealing.
(iv) In both the WT and the mutant enzyme, this decay shows a significant
solvent kinetic isotope effect, indicating that the decay reflects
a proton-assisted conversion to Compound I (Cpd I). (v) We confirm
that Cpd I formed during the annealing of the cryogenerated hydroperoxy
intermediate and that it is the active hydroxylating species in both
WT P450 2B4 and the F429H mutant. (vi) Our data also indicate that
the added H-bond of the mutation diminishes the reactivity of Cpd
I