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Structural Snapshots of an Engineered Cystathionine-?-lyase Reveal the Critical Role of Electrostatic Interactions in the Active Site.

ABSTRACT: Enzyme therapeutics that can degrade l-methionine (l-Met) are of great interest as numerous malignancies are exquisitely sensitive to l-Met depletion. To exhaust the pool of methionine in human serum, we previously engineered an l-Met-degrading enzyme based on the human cystathionine-?-lyase scaffold (hCGL-NLV) to circumvent immunogenicity and stability issues observed in the preclinical application of bacterially derived methionine-?-lyases. To gain further insights into the structure-activity relationships governing the chemistry of the hCGL-NLV lead molecule, we undertook a biophysical characterization campaign that captured crystal structures (2.2 Å) of hCGL-NLV with distinct reaction intermediates, including internal aldimine, substrate-bound, gem-diamine, and external aldimine forms. Curiously, an alternate form of hCGL-NLV that crystallized under higher-salt conditions revealed a locally unfolded active site, correlating with inhibition of activity as a function of ionic strength. Subsequent mutational and kinetic experiments pinpointed that a salt bridge between the phosphate of the essential cofactor pyridoxal 5'-phosphate (PLP) and residue R62 plays an important role in catalyzing ?- and ?-eliminations. Our study suggests that solvent ions such as NaCl disrupt electrostatic interactions between R62 and PLP, decreasing catalytic efficiency.

SUBMITTER: Yan W

PROVIDER: S-EPMC5376214 | biostudies-literature | 2017 Feb

REPOSITORIES: biostudies-literature

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Structural Snapshots of an Engineered Cystathionine-γ-lyase Reveal the Critical Role of Electrostatic Interactions in the Active Site.

Yan Wupeng W Stone Everett E Zhang Yan Jessie YJ

Biochemistry 20170203 6

Enzyme therapeutics that can degrade l-methionine (l-Met) are of great interest as numerous malignancies are exquisitely sensitive to l-Met depletion. To exhaust the pool of methionine in human serum, we previously engineered an l-Met-degrading enzyme based on the human cystathionine-γ-lyase scaffold (hCGL-NLV) to circumvent immunogenicity and stability issues observed in the preclinical application of bacterially derived methionine-γ-lyases. To gain further insights into the structure-activity ...[more]

PMID: 28106980

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Project description:Traditionally, hydrogen sulfide (H2S) was simply considered as a toxic and foul smelling gas, but recently H2S been brought into the spot light of cardiovascular research and development. Since the 1990s, H2S has been mounting evidence of physiological properties such as immune modification, vascular relaxation, attenuation of oxidative stress, inflammatory mitigation, and angiogenesis. H2S has since been recognized as the third physiological gaseous signaling molecule, along with CO and NO [65,66]. H2S is produced endogenously through several key enzymes, including cystathionine β-lyase (CBE), cystathionine γ-lyase (CSE), and 3-mercaptopyruvate sulfurtransferase (MST)/cysteine aminotransferase (CAT). These specific enzymes are expressed accordingly in various organ systems and CSE is the predominant H2S-producing enzyme in the cardiovascular system. The cystathionine γ-lyase (CSE)/H2S pathway has demonstrated various cardioprotective effects, including anti-atherosclerosis, anti-hypertension, pro-angiogenesis, and attenuation of myocardial ischemia-reperfusion injury. CSE exhibits its anti-atherosclerotic effect through 3 mechanisms, namely reduction of chemotactic factor inter cellular adhesion molecule-1 (ICAM-1) and CX3CR1, inhibition of macrophage lipid uptake, and induction of smooth muscle cell apoptosis via MAPK pathway. The CSE/H2S pathway's anti-hypertensive properties are demonstrated via aortic vasodilation through several mechanisms, including the direct stimulation of KATP channels of vascular smooth muscle cells (VSMCs), induction of MAPK pathway, and reduction of homocysteine buildup. Also, CSE/H2S pathway plays an important role in angiogenesis, particularly in increased endothelial cell growth and migration, and in increased vascular network length. In myocardial ischemia-reperfusion injuries, CSE/H2S pathway has shown a clear cardioprotective effect by preserving mitochondria function, increasing antioxidant production, and decreasing infarction injury size. However, CSE/H2S pathway's role in inflammation mitigation is still clouded, due to both pro and anti-inflammatory results presented in the literature, depending on the concentration and form of H2S used in specific experiment models.

Project description:Hydrogen sulfide (H2S) has recently been recognized as a novel gaseous transmitter with several anti-inflammatory properties. The role of host- derived H2S in infections by Pseudomonas aeruginosa was investigated in clinical and mouse models. H2S concentrations and survival was assessed in septic patients with lung infection. Animal experiments using a model of severe systemic multidrug-resistant P. aeruginosa infection were performed using mice with a constitutive knock-out of cystathionine-γ lyase (Cse) gene (Cse-/-) and wild-type mice with a physiological expression (Cse+/+). Experiments were repeated in mice after a) treatment with cyclophosphamide; b) bone marrow transplantation (BMT) from a Cse+/+ donor; c) treatment with H2S synthesis inhibitor aminooxyacetic acid (ΑΟΑΑ) or propargylglycine (PAG) and d) H2S donor sodium thiosulfate (STS) or GYY3147. Bacterial loads and myeloperoxidase activity were measured in tissue samples. The expression of quorum sensing genes (QS) was determined in vivo and in vitro. Cytokine concentration was measured in serum and incubated splenocytes. Patients survivors at day 28 had significantly higher serum H2S compared to non-survivors. A cut- off point of 5.3 μΜ discriminated survivors with sensitivity 92.3%. Mortality after 28 days was 30.9% and 93.7% in patients with H2S higher and less than 5.3 μΜ (p = 7 x 10-6). In mice expression of Cse and application of STS afforded protection against infection with multidrug-resistant P. aeruginosa. Cyclophosphamide pretreatment eliminated the survival benefit of Cse+/+ mice, whereas BMT increased the survival of Cse-/- mice. Cse-/- mice had increased pathogen loads compared to Cse+/+ mice. Phagocytic activity of leukocytes from Cse-/- mice was reduced but was restored after H2S supplementation. An H2S dependent down- regulation of quorum sensing genes of P.aeruginosa could be demonstrated in vivo and in vitro. Endogenous H2S is a potential independent parameter correlating with the outcome of P. aeruginosa. H2S provides resistance to infection by MDR bacterial pathogens.

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Structural Snapshots of an Engineered Cystathionine-?-lyase Reveal the Critical Role of Electrostatic Interactions in the Active Site.

Publications

Structural Snapshots of an Engineered Cystathionine-γ-lyase Reveal the Critical Role of Electrostatic Interactions in the Active Site.

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