Thermophilic proteins show substantially higher intrinsic thermal stability than their mesophilic counterparts. Amino acid composition is believed to alter the intrinsic stability of proteins. Several investigations and mutagenesis experiment have been carried out to understand the amino acid composition for the thermostability of proteins. This review presents some generalized features of amino acid composition found in thermophilic proteins, including an increase in residue hydrophobicity, a decrease in uncharged polar residues, an increase in charged residues, an increase in aromatic residues, certain amino acid coupling patterns and amino acid preferences for thermophilic proteins. The differences of amino acids composition between thermophilic and mesophilic proteins are related to some properties of amino acids. These features provide guidelines for engineering mesophilic protein to thermophilic protein.

Aims: This study examined the biotransformation pathway of ginsenoside Rb 1 by the fungus Esteya vermicola CNU 120806. Methods and Results: Ginsenosides Rb 1 and Rd were extracted from the root of Panax ginseng. Liquid fermentation and purified enzyme hydrolysis were employed to investigate the biotransformation of ginsenoside Rb 1 . The metabolites were identified and confirmed using NMR analysis as gypenoside XVII and gypenoside LXXV. A mole yield of 95Á4% gypenoside LXXV was obtained by enzymatic conversion (pH 5Á0, temperature 50°C). Ginsenoside Rd was used to verify the transformation pathway under the same reaction condition. The product Compound K (mole yield 49Á6%) proved a consecutive hydrolyses occurred at the C-3 position of ginsenoside Rb 1 . Conclusions: Strain CNU 120806 showed a high degree of specific b-glucosidase activity to convert ginsenosides Rb 1 and Rd to gypenoside LXXV and Compound K, respectively. The maximal activity of the purified glucosidase for ginsenosides transformation occurred at 50°C and pH 5Á0. Compared with its activity against pNPG (100%), the b-glucosidase exhibited quite lower level of activity against other aryl-glycosides. Enzymatic hydrolysate, gypenoside LXXV and Compound K were produced by consecutive hydrolyses of the terminal and inner glucopyranosyl moieties at the C-3 carbon of ginsenoside Rb 1 and Rd, giving the pathway: ginsenoside Rb 1 ? gypenoside XVII ? gypenoside LXXV; ginsenoside Rd?F 2 ? Compound K, but did not hydrolyse the 20-C, b-(1-6)-glucoside of ginsenoside Rb 1 and Rd. Significance and Impact of the Study: The results showed an important practical application on the preparation of gypenoside LXXV. Additionally, this study for the first time provided a high efficient preparation method for gypenoside LXXV without further conversion, which also gives rise to a potential commercial enzyme application.