Skaf MS

References (4)

Title : Mechanism and biomass association of glucuronoyl esterase: an alpha\/beta hydrolase with potential in biomass conversion - Zong_2022_Nat.Commun_13_1449
Author(s) : Zong Z , Mazurkewich S , Pereira CS , Fu H , Cai W , Shao X , Skaf MS , Larsbrink J , Lo Leggio L
Ref : Nat Commun , 13 :1449 , 2022
Abstract : Glucuronoyl esterases (GEs) are alpha/beta serine hydrolases and a relatively new addition in the toolbox to reduce the recalcitrance of lignocellulose, the biggest obstacle in cost-effective utilization of this important renewable resource. While biochemical and structural characterization of GEs have progressed greatly recently, there have yet been no mechanistic studies shedding light onto the rate-limiting steps relevant for biomass conversion. The bacterial GE OtCE15A possesses a classical yet distinctive catalytic machinery, with easily identifiable catalytic Ser/His completed by two acidic residues (Glu and Asp) rather than one as in the classical triad, and an Arg side chain participating in the oxyanion hole. By QM/MM calculations, we identified deacylation as the decisive step in catalysis, and quantified the role of Asp, Glu and Arg, showing the latter to be particularly important. The results agree well with experimental and structural data. We further calculated the free-energy barrier of post-catalysis dissociation from a complex natural substrate, suggesting that in industrial settings non-catalytic processes may constitute the rate-limiting step, and pointing to future directions for enzyme engineering in biomass utilization.
ESTHER : Zong_2022_Nat.Commun_13_1449
PubMedSearch : Zong_2022_Nat.Commun_13_1449
PubMedID: 35304453
Gene_locus related to this paper: opitp-b1zmf4

Title : Transition Path Sampling Study of the Feruloyl Esterase Mechanism - Silveira_2021_J.Phys.Chem.B__
Author(s) : Silveira RL , Knott BC , Pereira CS , Crowley MF , Skaf MS , Beckham GT
Ref : J Phys Chem B , : , 2021
Abstract : Serine hydrolases cleave peptide and ester bonds and are ubiquitous in nature, with applications in biotechnology, in materials, and as drug targets. The serine hydrolase two-step mechanism employs a serine-histidine-aspartate/glutamate catalytic triad, where the histidine residue acts as a base to activate poor nucleophiles (a serine residue or a water molecule) and as an acid to allow the dissociation of poor leaving groups. This mechanism has been the subject of debate regarding how histidine shuttles the proton from the nucleophile to the leaving group. To elucidate the reaction mechanism of serine hydrolases, we employ quantum mechanics/molecular mechanics-based transition path sampling to obtain the reaction coordinate using the Aspergillus niger feruloyl esterase A (AnFaeA) as a model enzyme. The optimal reaction coordinates include terms involving nucleophilic attack on the carbonyl carbon and proton transfer to, and dissociation of, the leaving group. During the reaction, the histidine residue undergoes a reorientation on the time scale of hundreds of femtoseconds that supports the "moving histidine" mechanism, thus calling into question the "ring flip" mechanism. We find a concerted mechanism, where the transition state coincides with the tetrahedral intermediate with the histidine residue pointed between the nucleophile and the leaving group. Moreover, motions of the catalytic aspartate toward the histidine occur concertedly with proton abstraction by the catalytic histidine and help stabilize the transition state, thus partially explaining how serine hydrolases enable poor nucleophiles to attack the substrate carbonyl carbon. Rate calculations indicate that the second step (deacylation) is rate-determining, with a calculated rate constant of 66 s(-1). Overall, these results reveal the pivotal role of active-site dynamics in the catalytic mechanism of AnFaeA, which is likely similar in other serine hydrolases.
ESTHER : Silveira_2021_J.Phys.Chem.B__
PubMedSearch : Silveira_2021_J.Phys.Chem.B__
PubMedID: 33616402
Gene_locus related to this paper: aspni-FAEA

Title : Characterization and engineering of a plastic-degrading aromatic polyesterase - Austin_2018_Proc.Natl.Acad.Sci.U.S.A_115_E4350
Author(s) : Austin HP , Allen MD , Donohoe BS , Rorrer NA , Kearns FL , Silveira RL , Pollard BC , Dominick G , Duman R , El Omari K , Mykhaylyk V , Wagner A , Michener WE , Amore A , Skaf MS , Crowley MF , Thorne AW , Johnson CW , Woodcock HL , McGeehan JE , Beckham GT
Ref : Proc Natl Acad Sci U S A , 115 :E4350 , 2018
Abstract : Poly(ethylene terephthalate) (PET) is one of the most abundantly produced synthetic polymers and is accumulating in the environment at a staggering rate as discarded packaging and textiles. The properties that make PET so useful also endow it with an alarming resistance to biodegradation, likely lasting centuries in the environment. Our collective reliance on PET and other plastics means that this buildup will continue unless solutions are found. Recently, a newly discovered bacterium, Ideonella sakaiensis 201-F6, was shown to exhibit the rare ability to grow on PET as a major carbon and energy source. Central to its PET biodegradation capability is a secreted PETase (PET-digesting enzyme). Here, we present a 0.92 A resolution X-ray crystal structure of PETase, which reveals features common to both cutinases and lipases. PETase retains the ancestral alpha/beta-hydrolase fold but exhibits a more open active-site cleft than homologous cutinases. By narrowing the binding cleft via mutation of two active-site residues to conserved amino acids in cutinases, we surprisingly observe improved PET degradation, suggesting that PETase is not fully optimized for crystalline PET degradation, despite presumably evolving in a PET-rich environment. Additionally, we show that PETase degrades another semiaromatic polyester, polyethylene-2,5-furandicarboxylate (PEF), which is an emerging, bioderived PET replacement with improved barrier properties. In contrast, PETase does not degrade aliphatic polyesters, suggesting that it is generally an aromatic polyesterase. These findings suggest that additional protein engineering to increase PETase performance is realistic and highlight the need for further developments of structure/activity relationships for biodegradation of synthetic polyesters.
ESTHER : Austin_2018_Proc.Natl.Acad.Sci.U.S.A_115_E4350
PubMedSearch : Austin_2018_Proc.Natl.Acad.Sci.U.S.A_115_E4350
PubMedID: 29666242
Gene_locus related to this paper: idesa-peth

Title : Enzyme microheterogeneous hydration and stabilization in supercritical carbon dioxide - Silveira_2012_J.Phys.Chem.B_116_5671
Author(s) : Silveira RL , Martinez J , Skaf MS , Martinez L
Ref : J Phys Chem B , 116 :5671 , 2012
Abstract : Supercritical carbon dioxide is a promising green-chemistry solvent for many enzyme-catalyzed chemical reactions, yet the striking stability of some enzymes in such unconventional environments is not well understood. Here, we investigate the stabilization of the Candida antarctica Lipase B (CALB) in supercritical carbon dioxide-water biphasic systems using molecular dynamics simulations. The preservation of the enzyme structure and optimal activity depend on the presence of small amounts of water in the supercritical dispersing medium. When the protein is at least partially hydrated, water molecules bind to specific sites on the enzyme surface and prevent carbon dioxide from penetrating its catalytic core. Strikingly, water and supercritical carbon dioxide cover the protein surface quite heterogeneously. In the first solvation layer, the hydrophilic residues at the surface of the protein are able to pin down patches of water, whereas carbon dioxide solvates preferentially hydrophobic surface residues. In the outer solvation shells, water molecules tend to cluster predominantly on top of the larger water patches of the first solvation layer instead of spreading evenly around the remainder of the protein surface. For CALB, this exposes the substrate-binding region of the enzyme to carbon dioxide, possibly facilitating diffusion of nonpolar substrates into the catalytic funnel. Therefore, by means of microheterogeneous solvation, enhanced accessibility of hydrophobic substrates to the active site can be achieved, while preserving the functional structure of the enzyme. Our results provide a molecular picture on the nature of the stability of proteins in nonaqueous media.
ESTHER : Silveira_2012_J.Phys.Chem.B_116_5671
PubMedSearch : Silveira_2012_J.Phys.Chem.B_116_5671
PubMedID: 22497454