ORIGINAL PAPER Heterogeneity of quaternary structure of glucosamine-6-phosphate deaminase from Giardia lamblia

Abstract The oligoHis-tagged versions of glucosamine-6-phosphate deaminase fromGiardia lamblia (GlmNagB-HisN, GlmNagB-HisC) were constructed and purified to hear homo-geneity, and their kinetic and structural properties were com-pared to those of the wild-type enzyme (GlmNagB). Introduc-tion of the oligoHis tag at the GlmNagB C-terminus resulted in almost complete loss of the catalytic activity, while the catalytic properties of GlmNagB-HisN and GlmNagB were very similar. The recombinant and wild-type enzyme exhibits heterogeneity of the quaternary structure and in solution exists in three interconvertible forms, namely, monomeric, homodi-meric, and homotetrameric. Although the monomeric form is prevalent, the monomer/dimer/tetramer ratios depended on protein concentration and fell within the range from 72:27:1 to 39:23:38. The enzyme is fully active in each of the oligo-meric structures, efficiently catalyzes synthesis of D-glucos-amine-6-phosphate from D-fructose-6-phosphate and ammo-nia, and its activity is not modified by GlcNAc6P, UDP-GlcNAc, or UDP-GalNAc. GlcN6P deaminase of G. lamblia represents a novel structural and functional type of enzyme of the NagB subfamily