Structure-based stabilization of an enzyme: the case of penicillin acylase from Alcaligenes faecalis

The modeled structure of penicillin acylase from Alcaligenes faecali (AFPGA) was constructed by comparative modeling with the Modeller program. Candidate positions that could be replaced with cysteine were estimated by scanning the modeled structure of AFPGA with the program MODIP (modeling disulfide bond in protein). The mutant Q3C/P751C had a higher optimum temperature by three degrees than that of the wild type AFPGA. The half life of the double mutant Q3C/P751C at 55 degrees C was increased by 50%. To our knowledge, this was the first structure-based genetic modification of AFPGA.     

Enhanced <Emphasis Type="SmallCaps">l</Emphasis>-phenylalanine production by recombinant <Emphasis Type="Italic">Escherichia coli</Emphasis> BR-42 (pAP-B03) resistant to bacteriophage BP-1 via a two-stage feeding approach

The l-phenylalanine (l-Phe) production by Escherichia coli WSH-Z06 (pAP-B03) was frequently prevented by bacteriophage BP-1 infestation. To cope with the bacteriophage BP-1 problem for an improved l-Phe production, one bacteriophage BP-1-resistant mutant, E. coli BR-42, was obtained from 416 mutant colonies of E. coli WSH-Z06 after N-methyl-N’-nitro-N-nitrosoguanidine (NTG) mutagenesis by selection for resistance to bacteriophage BP-1. The recombinant E. coli BR-42-carrying plasmid pAP-B03 had a high capacity in l-Phe production and a remarkable tolerance to 1 × 10¹⁰ pfu (plaque-forming unit)/ml bacteriophage stock. For an enhanced l-Phe production by E. coli BR-42 (pAP-B03), the effects of different feeding strategies including pH–stat, constant rate feeding, linear decreasing rate feeding, and exponential feeding on l-Phe production were investigated; and a two-stage feeding strategy, namely exponential feeding at μ _set = 0.18 h⁻¹ in the first 20 h and a following linear varying rate feeding with F = (−0.55 × t + 18.6) ml/h, was developed to improve l-Phe production. With this two-stage feeding approach, a maximum l-Phe titer of 57.63 g/l with a high l-Phe productivity (1.15 g/l/h) was achieved, which was 15% higher than the highest level (50 g/l) reported so far according to our knowledge. The recombinant E. coli BR-42 (pAP-B03) is a potential l-Phe over-producer in substantial prevention of bacteriophage BP-1 infestation compared to its parent strain WSH-Z06 (pAP-B03).     

PACS和远程放射系统的发展和联系

本文综述了PACS和远程放射系统的构成及其关键技术,阐述了它们的联系和区别,以及两者目前集成情况,并对两者可能的集成模型进行了探讨。     

Mitochondrial quality control protects photoreceptors against oxidative stress in the H2O2-induced models of retinal degeneration diseases

Retinal degeneration diseases (RDDs) are common and devastating eye diseases characterized by the degeneration of photoreceptors, which are highly associated with oxidative stress. Previous studies reported that mitochondrial dysfunction is associated with various neurodegenerative diseases. However, the role of mitochondrial proteostasis mainly regulated by mitophagy and mitochondrial unfolded protein response (mtUPR) in RDDs is unclear. We hypothesized that the mitochondrial proteostasis is neuroprotective against oxidative injury in RDDs. In this study, the data from our hydrogen peroxide (H₂O₂)-treated mouse retinal cone cell line (661w) model of RDDs showed that nicotinamide riboside (NR)-activated mitophagy increased the expression of LC3B II and PINK1, and promoted the co-localization of LC3 and mitochondria, as well as PINK1 and Parkin in the H₂O₂-treated 661w cells. However, the NR-induced mitophagy was remarkably reversed by chloroquine (CQ) and cyclosporine A (CsA), mitophagic inhibitors. In addition, doxycycline (DOX), an inducer of mtUPR, up-regulated the expression of HSP60 and CHOP, the key proteins of mtUPR. Activation of both mitophagy and mtUPR increased the cell viability and reduced the level of apoptosis and oxidative damage in the H₂O₂-treated 661w cells. Furthermore, both mitophagy and mtUPR played a protective effect on mitochondria by increasing mitochondrial membrane potential and maintaining mitochondrial mass. By contrast, the inhibition of mitophagy by CQ or CsA reversed the beneficial effect of mitophagy in the H₂O₂-treated 661w cells. Together, our study suggests that the mitophagy and mtUPR pathways may serve as new therapeutic targets to delay the progression of RDDs through enhancing mitochondrial proteostasis.Subject terms: Cell death, Diseases