Production of Oligosaccharides By Microorganisms
The present invention relates to the enzymatic synthesis of oligosaccharides, including sialylated product saccharides. In particular, it relates to the use of recombinant cells to take up low cost precursors such as glucose, pyruvate and N-actyl-glucosamine, and to synthesize activated sugar moieties that are used in oligosaccharide synthesis. The methods make possible the synthesis of many oligosaccharides using microorganisms and readily available, relatively inexpensive starting materials.
1 . A method of producing an oligosaccharide, the method comprising the step of culturing a microorganism in a culture medium comprising a glucose moiety, wherein the microorganism comprises
a heterologous galactosyltransferase activity, wherein the galactosyltransferase activity catalyzes the transfer of a galactose moiety from an activated galactose molecule to the glucose moiety to form a disaccharide.
2 . The method of claim 1 , wherein the microorganism further comprises a heterologous enzymatic system for synthesizing an activated galactose moiety from glucose.
3 . The method of claim 1 , wherein the oligosaccharide is lactose.
4 . The method of claim 1 , wherein the glucose moiety is glucose or N-acetylglucosamine (GlcNAc).
5 . The method of claim 1 , wherein the galactosyltransferase activity is selected from the group consisting of β1,3-galactosyltransferase and β1,4-galactosyltransferase.
6 . The method of claim 1 , wherein the microorganism further comprises a second heterologous glycosyltransferase, wherein the second glycosyltransferase catalyzes transfer of an activated sugar moiety to the disaccharide.
7 . The method of claim 6 , wherein the second heterologous glycosyltransferase is a sialyltransferase.
8 . The method of claim 7 , further comprising a heterologous fucosyltransferase.
9 . The method of claim 7 , wherein the culture medium further comprises N-acetylglucosamine (GlcNAc),
wherein the microorganism further comprises
b) an enzymatic system for synthesizing sialic acid from N-acetylglucosamine,
c) a CMP-sialic acid synthase polypeptide, and
d) a sialyltransferase polypeptide, wherein culture takes places under conditions suitable for synthesizing an activated sialic acid molecule and wherein the sialyltransferase polypeptide catalyzes the transfer of a sialic acid moiety from the activated sialic acid molecule to the lactose moiety to produce the oligosaccharide.
10 . The method of claim 6 , wherein the second heterologous glycosyltransferase is selected from the group consisting of a fucosyltransferase, an N-acetylglucosaminyl (GlcNAc) transferase, an N-acetylgalactosaminyl (GalNAc) transferase, and an α1,4-galactosyltransferase.
11 . A method of producing a sialylated product saccharide, said method comprising the step of:
growing a microorganism in a culture media comprising N-acetylglucosamine and an acceptor substrate, wherein said microorganism comprises:
a) an enzymatic system for synthesizing sialic acid from N-acetylglucosamine,
b) a CMP-sialic acid synthase polypeptide, and
c) a sialyltransferase polypeptide, wherein growth takes places under conditions suitable for synthesizing an activated sialic acid molecule and wherein the sialyltransferase polypeptide catalyzes the transfer of a sialic acid moiety from the activated sialic acid molecule to the acceptor substrate to produce the sialylated product saccharide.
12 . The method of claim 11 , wherein the enzymatic system for synthesizing sialic acid comprises an N-acetylglucosamine (GlcNAc) epimerase polypeptide and an N-acetyl neuraminic acid condensing polypeptide.
13 . The method of claim 12 , wherein the GlcNAc epimerase polypeptide is a heterologous protein.
14 . The method of claim 12 , wherein the N-acetyl neuraminic acid condensing polypeptide is a heterologous protein.
15 . The method of claim 11 , wherein the enzymatic system for synthesizing sialic acid comprises a UDP-GlcNAc epimerase polypeptide and a sialate synthase polypeptide.
16 . The method of claim 15 , wherein the UDP-GlcNAc epimerase polypeptide or the sialate synthase polypeptide is a heterologous protein.
17 . The method of claim 11 , wherein the CMP-sialic acid synthase polypeptide is a heterologous protein.
18 . The method of claim 11 , wherein the sialyltransferase polypeptide is a heterologous protein.
19 . The method of claim 11 , wherein the acceptor substrate is a monosaccharide selected from the group consisting of glucose, galactose, lactose, and mannose.
20 . The method of claim 11 , wherein the acceptor saccharide is lactose and the sialylated product sugar is sialylactose.
21 . The method of claim 11 , wherein the culture medium further comprises pyruvate.
22 . The method of claim 11 , wherein the sialylated product is produced on a commercial scale.
23 . The method of claim 11 , wherein the bacterium further comprises a heterologous CTP synthetase polypeptide.
24 . The method of claim 12 , wherein the GlcNAc epimerase polypeptide is a heterologous protein, the N-acetyl neuraminic acid condensing polypeptide is a heterologous protein, the CMP-sialic acid synthase polypeptide is a heterologous protein, and the sialyltransferase polypeptide is a heterologous protein.