PssJ Is a Terminal Galactosyltransferase Involved in the Assembly of the Exopolysaccharide Subunit in Rhizobium Leguminosarum bv. Trifolii

• Published in: International journal of molecular sciences 2020-10, Vol.21 (20), p.7764
• Main Authors: Marczak, Małgorzata, Wójcik, Magdalena, Żebracki, Kamil, Turska-Szewczuk, Anna, Talarek, Kamila, Nowak, Dominika, Wawiórka, Leszek, Sieńczyk, Marcin, Łupicka-Słowik, Agnieszka, Bobrek, Kamila, Romańczuk, Marceli, Koper, Piotr, Mazur, Andrzej
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Biofilms; Biosynthesis; Carbohydrates; Chromosome deletion; Deletion mutant; Enzymes; exopolysaccharide; Exopolysaccharides; Galactose; Galactose - chemistry; Galactose - metabolism; Galactosyltransferases - genetics; Galactosyltransferases - metabolism; Genes; Glucose; glycosyltransferase; Host-Pathogen Interactions; Membrane proteins; Membranes; Mutants; Mutation; Nodules; Plant Root Nodulation - genetics; Polymerization; Polysaccharides, Bacterial - chemistry; Polysaccharides, Bacterial - metabolism; Proteins; Rhizobium; Rhizobium leguminosarum; Rhizobium leguminosarum - enzymology; Rhizobium leguminosarum - genetics; Rhizobium leguminosarum - physiology; Root Nodules, Plant - genetics; Root Nodules, Plant - microbiology; symbiosis; Symbiosis - genetics; Trifolium - microbiology
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms21207764

bv. produces exopolysaccharide (EPS) composed of glucose, glucuronic acid, and galactose residues at a molar ratio 5:2:1. A majority of genes involved in the synthesis, modification, and export of exopolysaccharide are located in the chromosomal Pss-I region. In the present study, a Δ deletion mutant was constructed and shown to produce EPS lacking terminal galactose in the side chain of the octasaccharide subunit. The lack of galactose did not block EPS subunit translocation and polymerization. The delivery of the gene restored the production of galactose-containing exopolysaccharide. The mutant was compromised in several physiological traits, e.g., motility and biofilm production. An impact of the mutation and changed EPS structure on the symbiotic performance was observed as improper signaling at the stage of molecular recognition, leading to formation of a significant number of non-infected empty nodules. Terminal galactosyltransferase PssJ was shown to display a structure typical for the GT-A class of glycosyltransferases and interact with other GTs and Wzx/Wzy system proteins. The latter, together with PssJ presence in soluble and membrane protein fractions indicated that the protein plays its role at the inner membrane interface and as a component of a larger complex.