Overexpression and characterization of two unknown proteins, YicI and YihQ, originated from Escherichia coli

Substrate Recognition of Escherichia coli YicI (.ALPHA.-Xylosidase)

“…9) YicI is a typical α xylosidase. 10) Although YihQ hydrolyzes natural substrates, such as maltose and isomaltose, with quite low velocity, the protein evidently hydrolyzes an α glucopyranosyl fluoride, thereby being defined as an α glucosidase. 10) Although GH 31 contains such intriguing enzymes, the 17) and α glucosidase from Sulfolobus solfataricus, 18) have been determined.…”

“…10) Although YihQ hydrolyzes natural substrates, such as maltose and isomaltose, with quite low velocity, the protein evidently hydrolyzes an α glucopyranosyl fluoride, thereby being defined as an α glucosidase. 10) Although GH 31 contains such intriguing enzymes, the 17) and α glucosidase from Sulfolobus solfataricus, 18) have been determined. Biochemical properties of YicI have been also characterized thoroughly 10,17,19 21) as well as the structural studies, so that YicI is now one of the most representative enzymes in GH 31.…”

“…10) The enzyme is stable from pH 4.7 to 10.1 after incubation at 4 C for 24 h and is stable up to 47 C for 15 min of heat treatment, and totally loses its activity at 65 C. 10 have no effect on the hydrolytic activity of YicI. 17) The relative molecular mass of YicI is estimated to be 88,000 by SDS polyacrylamide gel electrophoresis (SDS PAGE) but is measured to be 530,000 by gel filtration chromatography, indicating that YicI exists as a hexamer.…”

“…17) The relative molecular mass of YicI is estimated to be 88,000 by SDS polyacrylamide gel electrophoresis (SDS PAGE) but is measured to be 530,000 by gel filtration chromatography, indicating that YicI exists as a hexamer. 10) The relative values of the hydrolysis rates for 4 mM of α xyloside and α glucoside substrates with YicI 10) are shown in Table 1. YicI can hydrolyze α xylosyl fluoride 17,400 times more rapidly than α glucosyl fluoride.…”

“…22) These preferences indicate that binding energy at the subsite +1 sufficiently contributes to the catalysis in GH 31 enzymes. YicI cannot hydrolyze insoluble xyloglucan, 10) implying that YicI may have no carbohydrate binding domain. The enzyme hardly ever hydrolyzes maltose, isomaltose, isomaltotriose, panose or maltotriose.…”