Nitrilase-catalyzed hydrolysis of 2-chloronicotinonitrile (2-CN) is a promising approach for efficient synthesis of 2-chloronicotinic acid (2-CA). Development of nitrilase with ideal catalytic properties is crucial for the biosynthetic route with industrial potentail. Herein, a nitrilase from Rhodococcus zopfii ( Rz NIT), which showed much higher hydration activity than hydrolysis activity, was designed for efficient hydrolysis of 2-CN. Two residues (N165 and W167) significantly affecting the reaction specificity were precisely identified. By tuning these two residues, a single mutation of W167G with abolished hydration activity and 20-fold improved hydrolysis activity was obtained. Molecular dynamics simulation and molecular docking revealed that the mutation generated a larger binding pocket, causing the substrate 2-CN bound more deeply in the pocket and the formation of delocalized π bond between the residues W190 and Y196, which reduced the negative influence of steric hindrance and electron effect caused by chlorine substituent. With mutant W167G as biocatalyst, 100 mM 2-CN was exclusively converted into 2-CA within 16 h. The study provides useful guidance in nitrilase engineering for simultaneous improvement of reaction specificity and catalytic activity, which are highly desirable in value-added carboxylic acids production from nitriles hydrolysis. Importance 2-CA is an important building block for agrochemicals and pharmaceuticals with rapid increase in demand in recent years. It is currently manufactured from 3-cyanopyridine by chemical methods. However, during the final step of 2-CN hydrolysis under high temperature and strong alkaline conditions, by-product 2-CM was generated except for the target product, leading to low yield and tedious separation steps. Nitrilase-mediated hydrolysis is regarded as a promising alternative for 2-CA production, which proceeds under mild conditions. Nevertheless, nitrilase capable of efficient hydrolysis of 2-CN was not reported till now, since the enzymes showed either extremely low activity or surprisingly high hydration activity towards 2-CN. Herein, the reaction specificity of Rz NIT was precisely tuned through a single site mutation. The mutant exhibited remarkably enhanced hydrolysis activity without formation of by-products, providing a robust biocatalyst for 2-CA biosynthesis with industrial potential.

No abstract

No abstract

Although large-scale 3D reconstruction by photogrammetry has been well studied and applied, the reconstruction of night scenery in urban areas has not been thoroughly considered. At night, low-light conditions often cause the images to lack sharpness and high-dynamic range issue leads to saturation. The SFM reconstruction pipeline that works well in daylight is likely to recover only limited dense points of bright fragmented objects near artificial lighting. Here, we propose a novel solution based on registration and synthesis between the night-time reconstruction and that of the same region in daytime. A registration pipeline is developed for conformal matching of the day and night point clouds. For the coarse registration step, we use detected plane features to search and match 4-plane congruent sets. For the fine registration step, we consider the positions of windows, a commonly-occurring object cue in urban building scenes as markers for accurate positioning. This leads to final registration error less than 0.2 degrees in rotation, and 0.2% in scale and translation. Finally, we synthesize the daytime textured model and the night point clouds to produce vivid visual effects of urban night scenery.

No abstract