Bioconversion of Rare Sugars by Isomerases and Epimerases from Microorganisms

미생물 유래 당질관련 이성화효소 및 에피머효소를 이용한 희소당 생물전환

Abstract

The International Society of Rare Sugars (ISRS) defines rare sugars as monosaccharides and their derivatives that rarely occur in nature. Rare sugars have recently received much attention because of their many uses including low-calorie sweeteners, bulking agents, and antioxidants, and their various applications including as immunosuppressants in allogeneic rat liver transplantation, as potential inhibitors of various glycosidases and microbial growth, in ischemia-reperfusion injury repair in the rat liver, and in segmented neutrophil production without detrimental clinical effects. Because they rarely exist in nature, the production of rare sugars has been regarded as one of the most important research areas and, generally, they are produced by chemical synthesis. However, the production of rare sugars by bioconversion using enzymes from microorganisms has been receiving increased attention as an environmentally friendly alternative production method. In particular, D-allulose, D-allose, and D-tagatose are of interest as low-calorie sweeteners in various industries. To date, D-tagatose 3-epimerase, D-psicose 3-epimerase, and D-allulose 3-epimerase have been reported as D-allulose bioconversion enzymes, and L-rhamnose isomerase, Galactose 6-phosphate isomerase, and Ribose 5-phosphate isomerase have been identified as D-allose production enzymes. Elsewhere, D-tagatose has been produced by L-arabinose isomerase from various microorganisms. In this study, we report the production of D-allulose, D-allose, and D-tagatose by microorganism enzymes.

희소당(Rare Sugars)은 국제희소당학회(International Society of Rare Sugars, ISRS)에 의해 지구상에 극히 소량 존재하는 단당류 또는 단당 유도체로서 정의되어 있으며, 희소당이 보유하고 있는 저칼로리, 항암, 항염증 및 항산화와 같은 유용한 생리활성으로 인해 현대산업분야에서 높은 주목을 받고 있는 차세대 기능성 신소재이다. 희소당은 자연계에 존재의 희소성으로 인해 희소당의 원활한 공급을 위한 희소당 생산 연구는 무엇보다도 중요한 연구로서 인식되어져 있다. 일반적으로 희소당은 화학적 방법과 미생물 유래 효소를 이용한 생물학적 방법으로 생산이 가능한데, 친환경적이며 생산공정도 안전한 생물학적 방법이 최근에 많은 주목을 받고 있다. 현재까지 희소당은 약 50종류 이상이 보고되어져 있는데 저칼로리, 항산화, 설탕 유사 감도 및 감미 특성으로부터 D-Allulose, D-Allose, 그리고 D-Tagatose가 특히 많은 주목을 받고 있는 희소당으로서 알려져 있다. 본 연구에서는 식품산업 및 의약산업을 비롯하여 다양한 산업분야에서 향 후 높은 활용성이 기대되는 D-Allulose, D-Allose, 그리고 D-Tagatose에 대한 미생물 유래 효소를 이용한 생물전환 생산에 대하여 보고를 하고자 한다.

Fig. 1. Bio-conversion of D-allulsoe from D-fructose by enzymes from microorganisms. DTEase and DAEase mean D-tagatose 3-epimerase and D-Allulose 3-epimerase, respectively .

Fig. 2. Rare sugars produced by epimerization reaction of DTEase and DAEase. Various rare sugars can be produced by epimerization at a C-3 position on D,L-form aldo-hexoses, keto-hexoses, aldo-pentoses, and keto-pentoses by DTEase and DAEase from environmental microorganisms.

Fig. 3. Bio-conversion of D-allose from D-allulose by enzymes from microorganisms. RipB, LacAB, and Rhalase mean Ribose 5-phosphate isomerase, Galactose 6-phosphate isomerase, and L-rhamnose isomerase, respectively.

Fig. 4. Rare sugars produced by Isomerization reaction of Rhalase, RpiB, and LacAB. Various rare sugars can be produced by isomerization of aldo-hexoses and aldo-pentoses having hydroxyl groups oriented in the right-handed configuration at C-2, C-3 or C-2, C-3, C-4 position by Rhalase, RpiB, and LacAB from environmental microorganisms.

Fig. 5. Bio-conversion of D-tagatose from D-galactose by enzymes from microorganisms. Arabiase means L-arabinose isomerase.

Fig. 6. Rare sugars produced by Isomerization reaction of Arabiase. Various rare sugars can be produced by isomerization of aldo-hexoses and aldo-pentoses having hydroxyl groups oriented in the right-handed and lefthanded configuration at C-2 and C-3 position, respectively by Arabiase from environmental microorganisms.

Table 1. Functions and applications of rare sugars