13 research outputs found
Norcoclaurine synthase: the mechanism and biocatalytic potential of a Pictet-Spenglerase
In plants, the enzyme norcoclaurine synthase (NCS) catalyses the formation of (S)-
norcoclaurine via the Pictet–Spengler condensation of dopamine and 4-
hydroxyphenylacetaldehyde (4-HPAA). (S)-Norcoclaurine is the precursor to all
benzylisoquinoline alkaloids (BIAs), a diverse group of over 2500 natural products.
The aim of this project was to elucidate the mechanism of NCS in order to enable the
rational engineering of NCS activity. Variants of NCS were screened for activities with
various substrates, forming novel tetrahydroisoquinolines (THIQs). NCS was combined
with other enzymes in biocatalytic cascades to produce THIQs.
Initially, an N-terminally truncated NCS from Thalictrum flavum (Δ19TfNCS) was
expressed. Problems with the purification of Δ19TfNCS led to the use of a different
truncate, Δ29TfNCS. This enzyme and variants were expressed and purified. The
effect of mutations on the activity, kinetics and substrate specificity of Δ29TfNCS led to
the conclusion that NCS operates with a ‘dopamine-first’ mechanism. Computational
analysis, including molecular dynamics and docking experiments, supported this
conclusion. Furthermore, rational engineering of substrate specificity was
demonstrated.
Next, the biocatalytic potential of NCS was investigated. Biotransformation conditions,
such as enzyme or lysate loading, were optimised before demonstrative examples of
milligram scale biotransformations were performed. Then, NCS and a transaminase
were combined in a one-pot ‘triangular’ biocatalytic cascade to produce chiral BIAs. An
additional chemical step led to the one-pot formation of chiral
tetrahydroprotoberberines (berbines). The cascades were demonstrated on a milligram
preparative scale.
Methods for screening NCS mutants were examined: various enzyme preparations,
reaction conditions and reporter systems were tested and evaluated. Subsequently,
NCS mutants were screened for activities with numerous amines and aldehydes. NCS
activity was identified with some α-substituted aldehydes and ketones. Selected
mutants demonstrated an increase in activity compared to wild-type for these unusual
substrates. Notably, high conversions were revealed for cyclohexanone derivatives. A
number of resulting cyclohexane-spiro-THIQs were characterised
One-pot triangular chemoenzymatic cascades for the syntheses of chiral alkaloids from dopamine
We describe novel chemoenzymatic routes to (S)-benzylisoquinoline and (S)-tetrahydroprotoberberine alkaloids using the enzymes transaminase (TAm) and norcoclaurine synthase (NCS) in a one-pot, one-substrate ‘triangular’ cascade. Employment of up to two C–C bond forming steps allows for the rapid generation of molecular complexity under mild conditions
Generation of amine dehydrogenases with increased catalytic performance and substrate scope from ε-deaminating <i>L</i>-Lysine dehydrogenase
Amine dehydrogenases (AmDHs) catalyse the conversion of ketones into enantiomerically pure amines at the sole expense of ammonia and hydride source. Guided by structural information from computational models, we create AmDHs that can convert pharmaceutically relevant aromatic ketones with conversions up to quantitative and perfect chemical and optical purities. These AmDHs are created from an unconventional enzyme scaffold that apparently does not operate any asymmetric transformation in its natural reaction. Additionally, the best variant (LE-AmDH-v1) displays a unique substrate-dependent switch of enantioselectivity, affording S- or R-configured amine products with up to >99.9% enantiomeric excess. These findings are explained by in silico studies. LE-AmDH-v1 is highly thermostable (Tm of 69 °C), retains almost entirely its catalytic activity upon incubation up to 50 °C for several days, and operates preferentially at 50 °C and pH 9.0. This study also demonstrates that product inhibition can be a critical factor in AmDH-catalysed reductive amination