Biochemical Studies

The pssA Gene Encodes UDP-Glucose: Polyprenyl Phosphate-Glucosyl Phosphotransferase Initiating Biosynthesis of Rhizobium leguminosarum Exopolysaccharide

V. N. Ksenzenko1#, T. V. Ivashina2, Z. A. Dubeikovskaya2, S. G. Ivanov2, M. B. Nanazashvili3, T. N. Druzhinina4, N. A. Kalinchuk4 and V. N. Shibaev4

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1Institute of Protein Research, Russian Academy of Sciences, ul. Institutskaya 4, Pushchino, Moscow oblast, 142292, Russia;
2Skryabin Institute of Biochemistry and Physiology of Microorganisms, Russian Academy of Sciences, ul. Institutskaya 5, Pushchino, Moscow oblast, 142292, Russia;
3Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, ul. Institutskaya 3, Pushchino, Moscow oblast, 142292, Russia;
4Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninskii pr. 47, Moscow, 119992, Russia

Received: March 21, 2006; in final form: April 25, 2006

Abstract. Symbiotic nitrogen-fixing bacteria Rhizobium leguminosarum bv. viciae VF39 secrete an acidic heteropolysaccharide, the biosynthesis of which involves the stage of polyprenyl diphosphate octasaccharide formation with its carbohydrate fragment corresponding to the repeating polymer unit. The amino acid analysis of the product of the pssA gene, we have earlier identified, showed its homology to bacterial polyisoprenyl phosphate hexose 1-phosphate transferases catalyzing the formation of phosphodiester bonds between polyprenyl phosphates and hexose 1-phosphates, whose donors are nucleotide sugars. The immunoblotting demonstrated that Rhizobium cells synthesize a protein with a molecular mass of 25 kDa, which implies the translation of the open reading frame occurring from the second initiating codon followed by the protein processing. It was shown that PssA is an integral membrane-bound protein involved in glucose 1-phosphate transfer from UDP-glucose to polyprenyl phosphate to form polyprenyl diphosphate glucose. These results suggest that the pssA gene encodes UDP-glucose:polyprenyl phosphate-glucosyl phosphotransferase.

Key words: exopolysaccharidesglycosyl transferases, membrane-bound proteins, polyprenyl diphosphate sugars, Rhizobium leguminosarum

Russian Journal of Bioorganic Chemistry 2007, 33 (1): 150-155