TY - JOUR
T1 - The catalytic machinery of the FAD-dependent AtBBE-like protein 15 for alcohol oxidation
T2 - Y193 and Y479 form a catalytic base, Q438 and R292 an alkoxide binding site
AU - Messenlehner, Julia
AU - Hetman, Michael
AU - Tripp, Adrian
AU - Wallner, Silvia
AU - Macheroux, Peter
AU - Gruber, Karl
AU - Daniel, Bastian
N1 - Funding Information:
This work was supported by a grant from the Austrian Science Foundation (FWF) (Doctoral program ?Molecular Enzymology? W908 and P28678) to KG and PM. We would like to acknowledge the help of Marina Toplak by her expertise in methodology and scientific input.
Publisher Copyright:
© The Authors
PY - 2021/3/30
Y1 - 2021/3/30
N2 - Monolignol oxidoreductases are members of the berberine bridge enzyme–like (BBE-like) protein family (pfam 08031) that oxidize monolignols to the corresponding aldehydes. They are FAD-dependent enzymes that exhibit the para-cresolmethylhydroxylase-topology, also known as vanillyl oxidase-topology. Recently, we have reported the structural and biochemical characterization of two monolignol oxidoreductases from Arabidopsis thaliana, AtBBE13 and AtBBE15. Now, we have conducted a comprehensive site directed mutagenesis study for AtBBE15, to expand our understanding of the catalytic mechanism of this enzyme class. Based on the kinetic properties of active site variants and molecular dynamics simulations, we propose a refined, structure-guided reaction mechanism for the family of monolignol oxidoreductases. Here, we propose that this reaction is facilitated stepwise by the deprotonation of the allylic alcohol and a subsequent hydride transfer from the Cα-atom of the alkoxide to the flavin. We describe an excessive hydrogen bond network that enables the catalytic mechanism of the enzyme. Within this network Tyr479 and Tyr193 act concertedly as active catalytic bases to facilitate the proton abstraction. Lys436 is indirectly involved in the deprotonation as this residue determines the position of Tyr193 via a cation-π interaction. The enzyme forms a hydrophilic cavity to accommodate the alkoxide intermediate and to stabilize the transition state from the alkoxide to the aldehyde. By means of molecular dynamics simulations, we have identified two different and distinct binding modes for the substrate in the alcohol and alkoxide state. The alcohol interacts with Tyr193 and Tyr479 while Arg292, Gln438 and Tyr193 form an alkoxide binding site to accommodate this intermediate. The pH-dependency of the activity of the active site variants revealed that the integrity of the alkoxide binding site is also crucial for the fine tuning of the pKa of Tyr193 and Tyr479. Sequence alignments showed that key residues for the mechanism are highly conserved, indicating that our proposed mechanism is not only relevant for AtBBE15 but for the majority of BBE-like proteins.
AB - Monolignol oxidoreductases are members of the berberine bridge enzyme–like (BBE-like) protein family (pfam 08031) that oxidize monolignols to the corresponding aldehydes. They are FAD-dependent enzymes that exhibit the para-cresolmethylhydroxylase-topology, also known as vanillyl oxidase-topology. Recently, we have reported the structural and biochemical characterization of two monolignol oxidoreductases from Arabidopsis thaliana, AtBBE13 and AtBBE15. Now, we have conducted a comprehensive site directed mutagenesis study for AtBBE15, to expand our understanding of the catalytic mechanism of this enzyme class. Based on the kinetic properties of active site variants and molecular dynamics simulations, we propose a refined, structure-guided reaction mechanism for the family of monolignol oxidoreductases. Here, we propose that this reaction is facilitated stepwise by the deprotonation of the allylic alcohol and a subsequent hydride transfer from the Cα-atom of the alkoxide to the flavin. We describe an excessive hydrogen bond network that enables the catalytic mechanism of the enzyme. Within this network Tyr479 and Tyr193 act concertedly as active catalytic bases to facilitate the proton abstraction. Lys436 is indirectly involved in the deprotonation as this residue determines the position of Tyr193 via a cation-π interaction. The enzyme forms a hydrophilic cavity to accommodate the alkoxide intermediate and to stabilize the transition state from the alkoxide to the aldehyde. By means of molecular dynamics simulations, we have identified two different and distinct binding modes for the substrate in the alcohol and alkoxide state. The alcohol interacts with Tyr193 and Tyr479 while Arg292, Gln438 and Tyr193 form an alkoxide binding site to accommodate this intermediate. The pH-dependency of the activity of the active site variants revealed that the integrity of the alkoxide binding site is also crucial for the fine tuning of the pKa of Tyr193 and Tyr479. Sequence alignments showed that key residues for the mechanism are highly conserved, indicating that our proposed mechanism is not only relevant for AtBBE15 but for the majority of BBE-like proteins.
KW - Alcohol oxidase
KW - Flavoprotein
KW - Reaction mechanism
KW - Structure-function relationship
UR - http://www.scopus.com/inward/record.url?scp=85100297690&partnerID=8YFLogxK
U2 - 10.1016/j.abb.2021.108766
DO - 10.1016/j.abb.2021.108766
M3 - Article
C2 - 33485849
AN - SCOPUS:85100297690
SN - 0003-9861
VL - 700
JO - Archives of Biochemistry and Biophysics
JF - Archives of Biochemistry and Biophysics
M1 - 108766
ER -