ENGINEERED ARYL SULFATE-DEPENDENT ENZYMES
The present invention provides several non-naturally occurring sulfotransferase enzymes that have been engineered to react with aryl sulfate compounds as sulfo group donors, instead of the natural substrate 3′-phosphoadenosine 5′-phosphosulfate (PAPS), and with heparosan-based polysaccharides, particularly heparan sulfate, as sulfo group acceptors. Each of the engineered sulfotransferase enzymes have a biological activity characterized by the position within the heparosan-based polysaccharide that receives the sulfo group, including glucosaminyl N-sulfotransferase activity, hexuronyl 2-O sulfotransferase activity, glucosaminyl 6-O sulfotransferase activity, or glucosaminyl 3-O sulfotransferase activity. Methods of using the engineered sulfotransferases to produce sulfated heparosan-based polysaccharides, including polysaccharides having anticoagulant activity, are also provided.
1 . A method of enzymatically forming a 2-O-sulfated heparan sulfate product, the method comprising the following steps:
(a) forming a reaction mixture comprising:
(i) a sulfo group donor, the sulfo group donor consisting of an aryl sulfate compound;
(ii) a heparosan-based polysaccharide, wherein the heparosan-based polysaccharide comprises at least one disaccharide unit consisting of a hexuronic acid residue and an N-unsubstituted glucosamine residue, wherein the hexuronic acid residue is selected from the group consisting of a glucuronic acid residue and an iduronic acid residue; and
(iii) a non-natural hexuronyl 2-O sulfotransferase enzyme (2OST), engineered to have sulfotransferase activity in the absence of 3′-phosphoadenosine 5′-phosphosulfate (PAPS), wherein the sulfotransferase activity comprises a transfer of the sulfo group from the aryl sulfate compound to the hexuronic acid residue;
(b) binding the aryl sulfate compound within the enzyme active site to form a protein-substrate complex; and
(c) catalyzing the transfer of the sulfo group from the aryl sulfate compound to the hexuronic acid residue, thereby forming the 2-O-sulfated heparan sulfate product.
2 . The method of claim 1 , wherein the hexuronic acid residue that receives the sulfo group from the aryl sulfate compound is an iduronic acid residue.
3 . The method of claim 1 , wherein the heparosan-based polysaccharide consists of disaccharide units having a hexuronic acid residue and an N-unsubstituted glucosamine residue.
4 . The method of claim 3 , wherein the hexuronic acid residue that receives the sulfo group from the aryl sulfate compound is an iduronic acid residue.
5 . The method of claim 3 , wherein the heparosan-based polysaccharide is chemically-desulfated heparin.
6 . The method of claim 1 , wherein the step of providing the heparosan-based polysaccharide comprises the steps of:
providing a starting mixture comprising heparosan;
chemically N-deacetylating at least one of the N-acetyl glucosamine residues within the heparosan, wherein the chemical N-deacetylation of an N-acetyl glucosamine residue forms an N-unsubstituted glucosamine residue; and
epimerizing at least one of the glucuronic acid residues within the heparosan using a heparosan-glucuronate C 5 -epimerase, wherein the epimerization of the glucuronic acid residue forms an iduronic acid residue.
7 . The method of claim 6 , wherein the epimerization step is performed prior to the chemical N-deacetylation step.
8 . The method of claim 1 , wherein the aryl sulfate compound is selected from the group consisting of p-nitrophenyl sulfate and 4-nitrocatechol sulfate.
9 . A protein-substrate complex, the protein-substrate complex comprising an aryl sulfate compound bound within the active site of a non-natural hexuronyl 2-O sulfotransferase enzyme (2OST) enzyme engineered to have sulfotransferase activity in the absence of 3′-phosphoadenosine 5′-phosphosulfate (PAPS), the sulfotransferase activity comprising the transfer of a sulfo group from an aryl sulfate compound to a heparosan-based polysaccharide to form a 2-O-sulfated heparan sulfate product.
10 . The protein-substrate complex of claim 9 , wherein the amino acid sequence of the non-natural 2OST enzyme comprises at least one amino acid sequence motif selected from the group consisting of SEQ ID NO: 248, SEQ ID NO: 249, and SEQ ID NO: 250.
11 . The protein-substrate complex of claim 10 , wherein the non-natural 2OST enzyme has an amino acid sequence comprising multiple mutations relative to conserved amino acid residues found in natural 2OST enzymes within enzyme class EC 2.8.2.-, wherein:
natural 2OST enzymes have sulfotransferase activity with heparan sulfate and a sulfo group donor, the sulfo group donor consisting of PAPS, to form a 2-O-sulfated heparan sulfate product; and
the amino acid sequence of the non-natural 2OST enzyme has at least 80% sequence identity with the amino acid sequence of a natural 2OST enzyme, the natural 2OST enzyme having amino acid sequence SEQ ID NO: 179.
12 . The protein-substrate complex of claim 11 , wherein the amino acid sequence of the non-natural 2OST enzyme comprises an amino acid sequence motif having the amino acid sequence of SEQ ID NO: 250.
13 . The protein-substrate complex of claim 11 , wherein the aryl sulfate compound is selected from the group consisting of p-nitrophenyl sulfate and 4-nitrocatechol sulfate.
14 . The protein-substrate complex of claim 10 , wherein the protein-substrate complex further comprises the heparosan-based polysaccharide, and the heparosan-based polysaccharide is also bound within the active site of the non-natural 2OST enzyme.
15 . The protein-substrate complex of claim 14 , wherein the heparosan-based polysaccharide comprises at least one disaccharide unit selected from the group consisting of:
a disaccharide unit having the structure of Formula IV,
a disaccharide unit having the structure of Formula V,
a disaccharide unit having the structure of Formula XI,
and a disaccharide unit having the structure of Formula XII,
16 . The protein-substrate complex of claim 9 , wherein the protein-substrate complex further comprises the heparosan-based polysaccharide, and at least a portion of the heparosan-based polysaccharide is also bound within the active site of the non-natural 2OST enzyme.
17 . The protein-substrate complex of claim 9 , wherein the aryl sulfate compound comprises a sulfuryl moiety, wherein the sulfuryl moiety is coordinated with a histidine residue engineered into the active site of the non-natural 2OST enzyme.
18 . The protein-substrate complex of claim 17 , wherein the amino acid sequence of the non-natural 2OST enzyme comprises the amino acid sequence motif having the amino acid sequence of SEQ ID NO: 250, and the sulfuryl moiety is coordinated with the histidine residue at position 4 of SEQ ID NO: 250.
19 . The protein-substrate complex of claim 9 , wherein the protein-substrate complex further comprises a C 5 -epimerase enzyme bound to the non-natural 2OST.
20 . The protein-substrate complex of claim 19 , wherein the C 5 -epimerase enzyme is a heparosan-glucuronate C 5 -epimerase.