br Conclusions In this work we

Conclusions In this work we have gained a substantial amount of structural and functional information on RHA-P, a novel recombinant rhamnosidase of the GH106 family recently isolated from the marine bacterium N. sp. PP1Y. The GH106 is a still poorly characterized family of glycosyl hydrolases and, to the best of our knowledge, only the crystal structure of protein BT0986 from Bacteroides thetaiotaomicron, has been solved so far. Therefore, in the absence of RHA-P crystal structure, the insights obtained from the combined approach involving a multiple sequences alignment and the homology modeling described in this work allowed to identify critical residues in the active site of RHA-P, which is of fundamental importance for the future fine-tuning of this enzymatic activity for biotechnological applications. Our results have highlighted that the biotechnological use of RHA-P, which has shown a remarkable catalytic efficiency on several flavonoids, encompass the use of either the purified protein or the whole recombinant C598-0466 expressing the His-tagged protein. Lastly, the optimization of the recombinant expression and purification protocol will undoubtedly pave the way in the near future to crystallization experiments that are required to shed light on the catalytic and structural features of this unique family of glycosyl hydrolases.
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Introduction Aggressive agents of chloride ions penetration into the concrete reinforcement is one of the most usual corrosive attacks in harsh environments that leads to several destructive consequences such as reduction of serviceability and strength. Cracks are the facilitator of the penetration process and certain routes for accession of moisture and oxygen to the reinforcement. Furthermore, the presence of enough chloride ions would cause the deterioration of passive layer adhered to steel rebar [1]. It is highly accepted that the incorporation of a pozzolanic material can reduce the permeability of concrete and enhance its resistance against chloride ions penetration [2]. The usage of supplementary cementitious materials such as rice husk ash has not only reduced the fuel demand for cement production and environmental pollution but also improved the mechanical properties and durability of concrete especially in aggressive environments [3]. Rice approximately covers 1% of land area of the earth and it is one of the main sources of food for billions of people [4]. One of the main agriculture industry residues is rice husk, which contains high amount of amorphous silica up to 85–95%. Rice husk ash (RHA) is a solid residue of rice husk controlled combustion, which shows the highest pozzolanic behavior among all plant residues productions [5]. Many of the previous studies have concentrated on investigating the optimum conditions for rice husk controlled combustion such as burning time and temperature, oxidizing procedures and heating rate in order to produce reactive ash [5]. In this regard, several studies [6], [7] have concluded that incineration of rice husk at temperatures below 500°C is imperfect and appreciable amount of unburned carbon is not expelled yet in this circumstances, which can result in adverse effects on ash pozzolanic activities. On the other hand, burning at temperatures higher than 700°C can lead to producing RHA with crystalline pozzolanic activity instead of amorphous one which is not preferable due to the reduction in reactivity [8], [9], [10], [11].