Cloning and characterization of a viral α2–3-sialyltransferase (vST3Gal-I) for the synthesis of sialyl Lewisx

摘要

Sialyl Lewis^x (SLe^x, Siaα2–3Galβ1–4(Fucα1–3)GlcNAcβOR) is an important sialic acid-containing carbohydrate epitope involved in many biological processes such as inflammation and cancer metastasis. In the biosynthetic process of SLe^x, α2–3-sialyltransferase-catalyzed sialylation generally proceeds prior to α1–3-fucosyltransferase-catalyzed fucosylation. For the chemoenzymatic synthesis of SLe^x containing different sialic acid forms, however, it would be more efficient if diverse sialic acid forms are transferred in the last step to the fucosylated substrate Lewis^x (Le^x). An α2–3-sialyltransferase obtained from myxoma virus-infected European rabbit kidney RK13 cells (viral α2–3-sialyltransferase (vST3Gal-I)) was reported to be able to tolerate fucosylated substrate Le^x. Nevertheless, the substrate specificity of the enzyme was only determined using partially purified protein from extracts of cells infected with myxoma virus. Herein we demonstrate that a previously reported multifunctional bacterial enzyme Pasteurella multocida sialyltransferase 1 (PmST1) can also use Le^x as an acceptor substrate, although at a much lower efficiency compared to nonfucosylated acceptor. In addition, N-terminal 30-amino-acid truncated vST3Gal-I has been successfully cloned and expressed in Escherichia coli Origami™ B(DE3) cells as a fusion protein with an N-terminal maltose binding protein (MBP) and a C-terminal His6-tag (MBP-Δ30vST3Gal-I-His6). The viral protein has been purified to homogeneity and characterized biochemically. The enzyme is active in a broad pH range varying from 5.0 to 9.0. It does not require a divalent metal for its α2–3-sialyltransferase activity. It has been used in one-pot multienzyme sialylation of Le^x for the synthesis of SLe^x containing different sialic acid forms with good yields.