58 4 br Experiments br Numerical simulations br Discussion b
Conclusions By large-caliber PELE with various d/D against RHA plate at low velocity of 415 m s−1, impact experiments against 30 mm RHA target were carried out. Numerical simulations were also conducted to monitor progress of PELE expansion and fragmentation in this condition. According to experimental and numerical results, an analytical model that taking an additional radial shock wave into consideration was presented to describe lateral effect, as well as an empirical approach for damage area on witness target. Further comparisons and discussion drew conclusions including:
Introduction RNA helicases are molecular motors that bind or remodel RNA and ribonucleoprotein (RNP) complexes in an ATP-dependent manner [, , ]. RNA helicases can be found in all the helicase superfamilies except for SF6 [4,5], exist in almost all living organisms, and play important roles in dsRNA unwinding, pre-mRNA editing, splicing, translation initiation, and other fundamental processes [, , ]. The majority of RNA helicases belonging to SF2 are comprised of five families, three of which are termed the DEAD-box, DEAH/RHA and viral DExH protein 58 4 . The DEAH/RHA family is the second largest RNA helicase with eight sequence motifs (I, Ia, Ib, II, III, IV, V and VI) that are conserved from bacteria to humans [, , , , ]. Motifs I, II and VI are related to ATP binding and hydrolysis, whereas, motifs Ia, Ib, IV and V may be involved in RNA binding . DEAH refers to the sequence of the helicase motif II, the equivalent of the DEAD-box, which reads D-E-A-H, for about half of the family members. RHA stands for RNA helicase A, the best-characterized protein of the remaining family members, all of which bear close resemblance to this enzyme on the sequence level. The DEAH/RHA family shares a conserved catalytic center formed by two RecA-like domains connected by a short flexible linker [1,14,15]. There are two genes encoding DEAH/RHA helicases in Escherichia coli (Ec), HrpA (Hypersensitive Response and Pathogenicity A) and HrpB (Hypersensitive Response and Pathogenicity B) . HrpA has been shown to be important in mRNA processing, ATP binding, hydrolysis ability and dsRNA unwinding in vitro [17,18]. HrpB was defined as a putative ATP-dependent RNA helicase, indispensable in RNA metabolism, bacteria motility, biofilm formation, survival on host leaves and the expression of type IV pili genes . In this study, we describe the first crystal structure of the EcHrpB-ADP•AlF4 complex, which is also the first structure of a prokaryotic DEAH/RHA helicase to be reported. Further, we found no similar structures when comparing the three-dimensional protein structure of the C-terminal extension (CTE) with the available database using the DALI server, suggesting that the CTE domain of HrpB has adopted a unique way of folding.
Materials and methods
Results and discussion
Declaration of interests
Acknowledgements We thank beamline scientists at BL17U1 of the Shanghai Synchrotron Radiation Facility and at BL18U1 and BL19U1 of the National Center for Protein Science Shanghai, for assistance with data collection; San-Hong Fan for critical comments on the manuscript. This work was supported by the National Natural Science Foundation of China (11574252 and 11774407) and International Associated Laboratory (LIA, ‘G-quadruplex-HELI’).
Introduction Concrete is one of the widely used construction materials for pavement construction. The present U.S. national highway system has about 45,000 miles of Interstate System, of which significant percent is concrete pavement . Production of concrete demands typically 10–15 percent of cement by volume . In 2015, about 82.8 million tons of cement was produced in the United States . This huge amount of cement production is responsible for a significant percentage of CO2 emissions in the environment. Each ton of cement production emits about one ton of CO2 , , and the cement industry is reported as the third largest CO2 producer in the world . As a result, incorporation of supplementary cementitious materials (SCM) in concrete has become a great concern nowadays. One of the potential SCMs is rice husk ash (RHA).