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J. Biol. Chem., Vol. 281, Issue 9, 5391-5397, March 3, 2006

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Critical Elements of Oligosaccharide Acceptor Substrates for the Pasteurella multocida Hyaluronan Synthase^*

Kellie J. Williams, Koen M. Halkes, Johannis P. Kamerling, and Paul L. DeAngelis¹

From the Department of Biochemistry and Molecular Biology, Oklahoma Center for Medical Glycobiology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104 and Bijvoet Center, Department of Bio-Organic Chemistry, Utrecht University, P.O. Box 80.075, NL-3508 TB Utrecht, The Netherlands

Three-dimensional structures are not available for polysaccharide synthases and only minimal information on the molecular basis for catalysis is known. The Pasteurella multocida hyaluronan synthase (PmHAS) catalyzes the polymerization of the alternating 1,3-N-acetylglucosamine-1,4-glucuronic acid sugar chain by the sequential addition of single monosaccharides to the non-reducing terminus. Therefore, PmHAS possesses both GlcNAc-transferase and glucuronic acid (GlcUA)-transferase activities. The recombinant Escherichia coli-derived PmHAS enzyme will elongate exogenously supplied hyaluronan chains in vitro with either a single monosaccharide or a long chain depending on the UDP-sugar availability. Competition studies using pairs of acceptors with distinct termini (where one oligosaccharide is a substrate that may be elongated, whereas the other cannot) were performed here; the lack of competition suggests that PmHAS contains at least two distinct acceptor sites. We hypothesize that the size of the acceptor binding pockets of the enzyme corresponds to the size of the smallest high efficiency substrates; thus we tested the relative activity of a series of authentic hyaluronan oligosaccharides and related structural analogs. The GlcUA-transferase site readily elongates (GlcNAc-GlcUA)₂, whereas the GlcNAc-transferase elongates GlcUA-Glc-NAc-GlcUA. The minimally sized oligosaccharides, elongated with high efficiency, both contain a trisaccharide with two glucuronic acid residues that enabled the identification of a synthetic, artificial acceptor for the synthase. PmHAS behaves as a fusion of two complete glycosyltransferases, each containing a donor site and an acceptor site, in one polypeptide. Overall, this information advances the knowledge of glycosaminoglycan biosynthesis as well as assists the creation of various therapeutic sugars for medical applications in the future.

Received for publication, September 22, 2005 , and in revised form, December 7, 2005.

^* This work was supported in part by National Science Foundation Grant MCB-9876193 and Oklahoma Center for Advancement of Science and Technology Health Research Grant HR02-036R (to P. L. D.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ To whom correspondence should be addressed: Dept. of Biochemistry and Molecular Biology, Univ. of Oklahoma Health Sciences Ctr., 940 Stanton L. Young Blvd., Oklahoma City, OK 73104. Tel.: 405-271-2227; Fax: 405-271-3092; E-mail: paul-deangelis{at}ouhsc.edu.

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