Data collection and refinement statistics.

<p>Values in parentheses are for the highest resolution shell.</p

Comparison of fold IV and fold I transaminases.

<p>A: Position of lysine relative to PLP in fold IV transaminases: in AT-ωTA (green), BCAT from human (1KT8, blue) or <i>E. coli</i> (1IYE, turquoise) and D-ATA from <i>Bacillus</i> sp. YM-1 (3DAA, brown). Ligands: blue: L-Ile-aldimine bound in human BCAT, turquoise: L-Glu-aldimine bound in BCAT from <i>E. coli</i>, brown: D-Ala-aldimine bound in D-ATA, green: L-Glu-aldimine bound in AT-ωTA, purple: docked acetophenone-aldimine in AT-ωTA. B: Position of lysine relative to PLP in fold I (<i>S</i>)-ω-transaminases: in PD-ωTA from <i>Paracoccus denitrificans</i> (4GRX, light green), PA-ωTA from <i>Pseudomonas aeruginosa</i> (4B98, turquoise) and several (<i>S</i>)-TAs identified from the Pdb by Steffen-Munsberg: from <i>Pseudomonas putida</i> (3A8U, pink), from <i>Mesorhizobium loti</i> (3GJU, yellow) and from <i>Silicobacter pomeroyi</i> (3HMU, brownish), in PD-ωTA the substrate, 5-aminopentanoate, is depicted in light green. The figures were prepared using the program PyMOL.</p

Localisation of the large and small binding pocket relative to PO₄ and O3’ of PLP and binding of the substrates’ substituents in different amino acid and amine transaminases (upper part: fold I aminotransferases, lower part: fold IV aminotransferases).

a<p>defined by the substrate size, in some structures the actual difference in the size of the pockets is very subtle.</p>b<p>proposed binding as seen in the scheme in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0087350#pone-0087350-g006" target="_blank">Figure 6</a>.</p>c<p>as observed in the solved structure of AT-ωTA.</p

Detailed reaction mechanism of transaminases.

<p>Detailed reaction mechanism of transaminases.</p

Crystal structure of AT-ωTA.

<p>A: Overview of the AT-ωTA dimer (chain A in green, chain B in grey), conserved regions are indicated in yellow, B: overview of the AT-ωTA dimer with the binding pockets indicated as orange spheres, C: small binding pocket amino acids (blue), D: large binding pocket amino acids (orange), E: PLP binding amino acids (green). The figures were prepared using the program PyMOL.</p

Relative activities calculated from the increase of acetophenone at 300-ωTA and mutants thereof (0.1 mM PLP, 5 mM <i>(R)-</i>α-methylbenzylamine, 5 mM pyruvate or 5 mM butanal, in 50 mM KPi, pH 7.5, 0.25 mg/mL of total lysate protein) at 25°C.

<p>The relative activities are referred to either the wild-type activity with pyruvate (0.8 U/mg lysate, dark grey bars) or butanal (0.1 U/mg lysate, light grey bars).</p

Schematic drawing of the localisation of the large and small binding pocket in AT-ωTA relative to PO₄ and O3’ of PLP and the binding of the substrates’ substituents.

<p>Schematic drawing of the localisation of the large and small binding pocket in AT-ωTA relative to PO₄ and O3’ of PLP and the binding of the substrates’ substituents.</p

Zoom into the loop Thr121-Val136 region of chain B in the structural alignment of the AT-ωTA structure (magenta) with other fold class IV transaminase structures (dark grey).

<p>For PDB-IDs see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0087350#pone.0087350.s001" target="_blank">Figure S2 in File S1</a>. The figure was prepared using the program PyMOL.</p

Crystal Structure of an (<i>R</i>)-Selective ω-Transaminase from <i>Aspergillus terreus</i>

<div><p>Chiral amines are important building blocks for the synthesis of pharmaceutical products, fine chemicals, and agrochemicals. ω-Transaminases are able to directly synthesize enantiopure chiral amines by catalysing the transfer of an amino group from a primary amino donor to a carbonyl acceptor with pyridoxal 5′-phosphate (PLP) as cofactor. In nature, (<i>S</i>)-selective amine transaminases are more abundant than the (<i>R</i>)-selective enzymes, and therefore more information concerning their structures is available. Here, we present the crystal structure of an (<i>R</i>)-ω-transaminase from <i>Aspergillus terreus</i> determined by X-ray crystallography at a resolution of 1.6 Å. The structure of the protein is a homodimer that displays the typical class IV fold of PLP-dependent aminotransferases. The PLP-cofactor observed in the structure is present in two states (i) covalently bound to the active site lysine (the internal aldimine form) and (ii) as substrate/product adduct (the external aldimine form) and free lysine. Docking studies revealed that (<i>R</i>)-transaminases follow a dual binding mode, in which the large binding pocket can harbour the bulky substituent of the amine or ketone substrate and the α-carboxylate of pyruvate or amino acids, and the small binding pocket accommodates the smaller substituent.</p></div

Proposed reaction mechanism.

<p>Reaction mechanism for the Friedel–Crafts alkylation catalyzed by SAM-dependent <i>C</i>-methyltransferases, CouO from <i>Streptomyces rishiriensis</i> and NovO from <i>Streptomyces spheroides</i>.</p