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Alkaline pectate lyases have biotechnological applications in plant fiber processing, such as ramie degumming. Previously, we characterized an alkaline pectate lyase from Bacillus clausii S10, named BacPelA, which showed potential for enzymatic ramie degumming because of its high cleavage activity toward methylated pectins in alkaline conditions. However, BacPelA displayed poor thermo-alkaline stability. Here, we report the 1.78 Å resolution crystal structure of BacPelA in apo form. The enzyme has the characteristic right-handed β-helix fold of members of the polysaccharide lyase 1 family and shows overall structural similarity to them, but it displays some differences in the details of the secondary structure and Ca2+-binding site. On the basis of the structure, 10 sites located in flexible regions and showing high B-factor and positive ΔTm values were selected for mutation, aiming to improve the thermo-alkaline stability of the enzyme. Following site-directed saturation mutagenesis and screening, mutants A238C, R150G, and R216H showed an increase in the T5015 value at pH 10.0 of 3.0 °C, 6.5 °C, and 7.0 °C, respectively, compared with the wild-type enzyme, interestingly accompanied by a 24.5%, 46.6%, and 61.9% increase in activity. The combined mutant R150G/R216H/A238C showed an 8.5 °C increase in the T5015 value at pH 10.0, and an 86.1% increase in the specific activity at 60 °C, with approximately doubled catalytic efficiency, compared with the wild-type enzyme. Moreover, this mutant retained 86.2% activity after incubation in ramie degumming conditions (4 h, 60 °C, pH 10.0), compared with only 3.4% for wild-type BacPelA. The combined mutant increased the weight loss of ramie fibers in degumming by 30.2% compared with wild-type BacPelA. This work provides a thermo-alkaline stable, highly active pectate lyase with great potential for application in the textile industry, and also illustrates an effective strategy for rational design and improvement of pectate lyases. [ABSTRACT FROM AUTHOR]

We propose an in situ technique for measuring an even aberration of lithographic projection optics. By using the Hopkins theory of partially coherent imaging and the thick-mask model, the linear relationship between the intensity difference of adjacent peaks in an alternating phase-shifting mask image and an even aberration is established by equations and verified by numerical results. The sensitivity of measuring the even aberration of lithographic projection optics based on this linear relationship is analyzed, and the measurement mark is designed accordingly. Measurement performance of the present technique is evaluated using the lithographic simulator PROLITH, which shows that the present technique is capable of measuring the even aberration of lithographic projection optics with ultrahigh measurement accuracy. OCIS codes: 050.5080, 110.3960, 120.3940.

Two types of retrograded eclogite (phengite‐bearing eclogite and garnet pyroxenite) within eclogite‐facies granitic gneisses are reported for the first time from the Younusisayi area of the South Altyn high to ultrahigh pressure (HP–UHP) metamorphic belt. These eclogites were studied using petrology, mineral chemistry, phase equilibrium modelling, and geochronology. The phengite‐bearing eclogite records five stages of metamorphism: (1) early prograde (Grt + Cpx + Amp + Rt + Qz) at conditions of P = 11.50–17.5 kbar, T = 665–740°C; (2) peak eclogite‐facies (Grt + Omp + Ph + Rt + Qz) at conditions of P > 24.2 kbar, T = 710–1000°C; (3) overprinting during retrograde transition to HP granulite‐facies conditions (Grt + Cpx ± Kfs + Pl + Rt + Qz) at P = 12.1–16.9 kbar and T = 760–890°C; (4) retrogression at granulite‐facies conditions (Grt + Cpx + Amp + Pl + Ilm + Qz) of P = 9.1–11.4 kbar, T = 730–840°C; and (5) amphibolite‐facies metamorphism (Amp + Pl + Ilm + Qz) during cooling and decompression. The garnet pyroxenite records four stages of metamorphism: (1) eclogite‐facies at conditions of P > 23.2 kbar, T = 775–965°C; (2) HP granulite‐facies conditions of P = 13.2–17.8 kbar and T = 836–912°C; (3) granulite‐facies conditions of P = 8.6–9.7 kbar, T = 739–783°C; and (4) amphibolite‐facies metamorphism. Zircon U–Pb dating and trace element analysis constrain eclogite‐facies metamorphism to c. 500 Ma, consistent with the age of the surrounding eclogite‐facies granitic gneiss (497.8 ± 2.7 Ma). Retrograde metamorphism ages of c. 460 Ma are interpreted as recording zircon growth after granulite‐facies metamorphism. The P–T–t path defines the integrated process of deep subduction and multistage exhumation and places constraints on the early Palaeozoic geodynamics of the South Altyn belt. Well‐preserved major and trace element zoning of garnets in the Ph‐bearing eclogites lacks evidence of significant thermal diffusion and may record garnet growth during deep subduction, immediately followed by very rapid exhumation. [ABSTRACT FROM AUTHOR]