Periplasmic α-amylase MalS (EC. 3.2.1.1), which belongs to glycoside hydrolase (GH) family 13 subfamily 19, is an integral component of the maltose utilization pathway in Escherichia coli K12 and used among Ecnterobacteriaceae for the effective utilization of maltodextrin. We present the crystal structure of MalS from E. coli and reveal that it has unique structural features of circularly permutated domains and a possible CBM69. The conventional C-domain of amylase consists of amino acids 120–180 (N-terminal) and 646–676 (C-terminal) in MalS, and the whole domain architecture shows the complete circular permutation of C-A-B-A-C in domain order. Regarding substrate interaction, the enzyme has a 6-glucosyl unit pocket binding it to the non-reducing end of the cleavage site. Our study found that residues D385 and F367 play important roles in the preference of MalS for maltohexaose as an initial product. At the active site of MalS, β-CD binds more weakly than the linear substrate, possibly due to the positioning of A402. MalS has two Ca2+ binding sites that contribute significantly to the thermostability of the enzyme. Intriguingly, the study found that MalS exhibits a high binding affinity for polysaccharides such as glycogen and amylopectin. The N domain, of which the electron density map was not observed, was predicted to be CBM69 by AlphaFold2 and might have a binding site for the polysaccharides. Structural analysis of MalS provides new insight into the structure–evolution relationship in GH13 subfamily 19 enzymes and a molecular basis for understanding the details of catalytic function and substrate binding of MalS.

Major components including total phenolic compounds, cellulose, starch and soluble sugar and physicochemical properties of radish breeding combinations were determined and statistically analyzed to evaluate their relationship and to develop radish cultivars targeting foreign market. Sixteen radish combinations selected for Chinese market were analyzed in color and total phenolic compounds, texture and cellulose, β-amylase activity and starch/soluble sugars. In addition, relationship between each component was estimated using Pearson correlation coefficients. Total phenolic contents of radish were 26.0±3.0 mg gallic acid equivalent per gram dry weight (dw). Correlation between brightness of surface and the total phenolic content was negative, but redness or yellowness showed positive correlation. Cellulose and starch contents were 17.9±2.6 g/100 g dw and 3.06±1.08 g/100 g dw, respectively. Those contents and the cutting force of radish showed positive relationship, but according to Pearson correlation coefficient, it was not statistically significant. Activity of β-amylase was 93.2±38.0 total unit/ g dw in average, and soluble sugar was detected as 195±49 mg•g-1 dw. Unexpectedly, the β-amylase activity and starch or soluble sugar contents showed no statistically significant correlation, which might be due to very short storage time of radishes before analysis. These results could be valuable information for the development of radish cultivars applicable for dried radish targeting Chinese market.