Low complexity MIMO equalization for long-haul SDM systems.

Space-division multiplexing (SDM) has been expected to support the continuous growth of transmission capacity. However, it suffers from high computation complexity that limits its physical implementations. In this paper, we propose and experimentally demonstrate a low-complexity MIMO equalization method to leverage the sparsity of weights and reduce the complexity by L1&L2-regularization in long-haul space-division multiplexing (SDM) systems. The L1-regularization finds the sparse solution of equalizer filters and substitutes it for optimal solution, reducing the complexity with performance degradation. On the other hand, the L2-regularization tends to produce a smoother estimation than L1 regularization and is therefore more robust to large variance. We conduct a 39.87-GBaud QPSK coherent optical transmission experiment based on a 4-core coupled-core fiber with the transmission distance from 1206-km to 7236-km. Comparisons on the equalization performance and computational complexity show that the sparse equalizer using L1&L2-regularization achieves a 30% reduction in complexity at the similar system performance, compared with the traditional time-domain MIMO.

[Ecosystem Carbon Storage in Hangzhou Bay Area Based on InVEST and PLUS Models].

The study of the relationship between the land use and carbon storage of ecosystem services is of great significance to regional carbon emission management. It can provide an important scientific basis for the management of regional ecosystem carbon pools and the formulation of policies for emission reduction and foreign exchange increases. The carbon storage component of the InVEST model and the PLUS model were used to study and predict the temporal and spatial variation characteristics of carbon storage in the ecological system and their relationship with land use type for the periods of 2000-2018 and 2018-2030 in the research area. The results were as follows:the carbon storage in 2000, 2010, and 2018 in the research area was 7.250×108, 7.227×108, and 7.241×108 t, respectively, which suggested that it first decreased and then increased. The change in land use pattern was the main cause of changed carbon storage in the ecological system, and the fast expansion of construction land resulted in the decrease of carbon storage. With its correspondence to land use patterns, the carbon storage in the research area demonstrated significant spatial differentiation and was characterized by low storage in the northeast and high storage in the southwest according to the demarcation line of carbon storage. The resulting prediction was that the carbon storage in 2030 will be 7.344×108 t, with an increase of 1.42% compared with that in 2018, owing mainly to increased forest land. Soil type and population were the two driving factors with the highest contribution to construction land, and soil type and DEM had the highest contribution to forest land.

Screening and characterization of a nitrilase with significant nitrile hydratase activity.

PURPOSE: We screened nitrilases with significant nitrile hydratase activity to exploit their potential in benzylic amide biosynthesis. We also investigated the factors affecting their hydration activity to support further research on benzylic amide production by nitrilase. METHODS: A sequence-based screening method using previously reported crucial positions identified to be essential for amide-forming capacity of nitrilase (referred to as "amide-formation hotspots") as molecular probes to identify putative amide-forming nitrilases. RESULTS: Based on the previously reported "amide-formation hotspots," we identified a nitrilase NitPG from Paraburkholderia graminis DSM 17151 that could produce a significant amount of mandelamide toward mandelonitrile and exhibited general hydration activity toward various benzylic nitriles. The time-course experiment with NitPG demonstrated that amide was also a true reaction product of nitrilase, suggesting that the nitrile catalysis by amide-forming nitrilase could be a post-transition state bifurcation-mediated enzymatic reaction. Further research demonstrated that low temperature, metal ion addition, and specific substrate structure could profoundly improve the amide formation capability of nitrilase. CONCLUSIONS: NitPG with broad hydration activity is a potential candidate for the enzymatic synthesis of benzylic amides for biotechnological applications. Studying the effect of nitrilase hydration activity could promote our understanding of the factors that influence amide and acid distribution.

Rational hinge engineering of carboxylic acid reductase from Mycobacterium smegmatis enhances its catalytic efficiency in biocatalysis.

BACKGROUND: Carboxylic acid reductases (CARs) represent useful tools for the production of aldehydes from ubiquitous organic carboxylic acids. However, the low catalytic efficiency of these enzymes hampers their application. METHODS: Herein, a CAR originating from Mycobacterium smegmatis was redesigned through rational hinge engineering to enhance the catalytic efficiency. RESULTS: Based on the unique domain architecture of CARs and their superfamily, a mutagenesis library of the hinge region was designed. The best mutant R505I/N506K showed a 6.57-fold improved catalytic efficiency. Molecular dynamics simulations showed the increased catalytic efficiency was due to the strong binding of the acyl-AMP complex with it. Meanwhile, the ε-nitrogen atom of Lys610 frequently interacted with the ribose-ring oxygen atom of the complex, the distance (d1) between them represents a great indicator for that. The d1 value was used as a nimble indicator to evaluate unexplored mutants of that region for enhanced activity by in silico mutational experiments. Overall, eight mutants were identified to show higher enhanced activity compared with wild-type enzyme and R505F/N506G showed the highest catalytic efficiency. CONCLUSION: Altogether, the two-step strategy used here provided useful references for the engineering of CARs and other similar multiple-domain enzymes.

Switching the secondary and natural activity of Nitrilase from Acidovorax facilis 72 W for the efficient production of 2-picolinamide.

OBJECTIVES: Catalytic promiscuity, or the ability to catalyze a secondary reaction, provides new opportunities for industrial biocatalysis by expanding the range of biocatalytic reactions. Some nitrilases converting nitriles to amides, referred to as the secondary activity, show great potential for amides production. And our goal was exploiting the amide-forming potential of nitrilases. RESULTS: In this study, we characterized and altered the secondary activity of nitrilase from Acidovorax facilis 72 W (Nit72W) towards different substrates. We increased the secondary activity of Nit72W towards 2-cyanopyridine by 196-fold and created activity toward benzonitrile and p-nitrophenylacetonitrile by modifying the active pocket. Surprisingly, the best mutant, W188M, completely converted 250 mM 2-cyanopyridine to more than 98% 2-picolinamide in 12 h with a specific activity of 90 U/mg and showed potential for industrial applications. CONCLUSIONS: Nit72W was modified to increase its secondary activity for the amides production, especially 2-picolinamide.

Switching the regioselectivity of two nitrilases toward succinonitrile by mutating the active center pocket key residues through a semi-rational engineering.

The 163Ala in bll6402NIT and 172Trp in blr3397NIT played a significant role in directing nitrilase regioselectivity. Amino acid mutation of two nitrilases at these two sites could alter the size of the active site pocket and further switch nitrilase regioselectivity toward succinonitrile, which lays the foundation for subsequent research on regioselective nitrilase towards several dinitriles.