Creation of enzyme variants displaying desirable catalytic performance usually necessitates tedious and time-consuming procedures for library generation and selection, which may be circumvented by a computational method based on a precise understanding of the reaction mechanism in the context of active site environment. Despite the great potential of ω-transaminases (ω-TAs) for asymmetric synthesis of chiral amines from ketones, it remains elusive why ω-TAs exhibit marginal activities for most ketones in contrast to their high activities for α-keto acids and aldehydes. To address this puzzling question, crystal structure determination and molecular modeling of ω-TAs were carried out to analyze docking orientations of the amino acceptors in the Michaelis complex. We found that ketones, unlike the reactive substrates, led to nonproductive binding complexes where the bound substrate was hardly accessible to a nucleophilic attack by the pyridoxamine cofactor to initiate reductive amination of the amino acceptor. This finding led us to perform in silico mutagenesis of the S-selective ω-TA from Ochrobactrum anthropi to ameliorate the unfavorable nucleophilic attack trajectory to structurally demanding ketones. The resulting variant, carrying L57A/W58A mutations, was predicted to allow an unprecedented re-face attack on butyrophenone, leading to 10 5 -fold activity improvement with no loss in stereoselectivity. This study is expected to provide an efficient computational strategy for creation of high-turnover ω-TA variants tailored for a target ketone by affording in silico assessment of the effect of active site mutation on an enzyme activity.

Asymmetricr eductivea mination of ketones using w-transaminases (w-TAs)offers apromising alternative to the chemocatalytic synthesiso f chiral amines.O ne fundamental challenge to the biocatalytic strategyi st he very low enzyme activities for most ketones compared with native substrates (i.e., <1% relativet op yruvate). Here we have demonstrated that as ingle point mutation in the active site of the (S)-selective w-TAf rom Ochrobactrum anthropi could induce ar emarkable acceleration of the amination reactionw ithout anyl oss in stereoselectivity and enzyme stability.M olecular modeling of quinonoid intermediates,a lanine scanning mutagenesis and kinetic analysis revealedthat the W58 residue acted as as tericb arrier to binding and catalytic turnover of ketone substrates. Removal of the steric strain by W58L substitution, which was selected by partials aturation mutagenesis,l ed to dramatica ctivity improvements for structurally diverse ketones (e.g.,3 40-fold increase in k cat /K M for acetophenone). TheW 58Lm utant afforded an efficient synthesis of enantiopure amines (i.e., >99% ee)u sing isopropylamine as an amino donor.

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psyllidae) is a vector for the causative agents of Huanglongbing, which threatens citrus production worldwide. This study reports and discusses the first D. citri transcriptomes, encompassing the three main life stages of D. citri, egg, nymph and adult. The transcriptomes were annotated using Gene Ontology (GO) and insecticide-related genes within each life stage were identified to aid the development of future D. citri insecticides. Transcriptome assemblies and other sequence data are available for download at the International Asian Citrus Psyllid Genome Consortium website [http://psyllid.org/download] and at NCBI [http://www.ncbi.nlm.nih.gov/bioproject/29447].

Methylosinus trichosporium OB3b (for "oddball" strain 3b) is an obligate aerobic methane-oxidizing alphaproteobacterium that was originally isolated in 1970 by Roger Whittenbury and colleagues. This strain has since been used extensively to elucidate the structure and function of several key enzymes of methane oxidation, including both particulate and soluble methane monooxygenase (sMMO) and the extracellular copper chelator methanobactin. In particular, the catalytic properties of soluble methane monooxygenase from M. trichosporium OB3b have been well characterized in context with biodegradation of recalcitrant hydrocarbons, such as trichloroethylene. The sequence of the M. trichosporium OB3b genome is the first reported from a member of the Methylocystaceae family in the order Rhizobiales.