The lipopolysaccharide (LPS) O-antigen structure of the plant pathogen Rhizobium radiobacter strain TT9 and its possible role in a plant-microbe interaction was investigated. The analyses disclosed the presence of two O-antigens, named Poly1 and Poly2. The repetitive unit of Poly2 constitutes a 4-α-l-rhamnose linked to a 3-α-d-fucose residue. Surprisingly, Poly1 turned out to be a novel type of biopolymer in which the repeating unit is formed by a monosaccharide and an amino-acid derivative, so that the polymer has alternating glycosidic and amidic bonds joining the two units: 4-amino-4-deoxy-3-O-methyl-d-fucose and (2'R,3'R,4'S)-N-methyl-3',4'-dihydroxy-3'-methyl-5'-oxoproline). Differently from the O-antigens of LPSs from other pathogenic Gram-negative bacteria, these two O-antigens do not activate the oxidative burst, an early innate immune response in the model plant Arabidopsis thaliana, explaining at least in part the ability of this R. radiobacter strain to avoid host defenses during a plant infection process.

carbohydrates, structure elucidation, saccharides, structural biology, Biopolymers

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7
1,4	xD3,4HO1,3MePro-5-oxo	175.6	72.3	77.7	76.6	176.5	30.5	22.0
1,3	Me	58.2
1	aDFucp4N	100.6	68.4	79.2	51.8	66.0	17.2
	Me	56.6


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7
1,4	xD3,4HO1,3MePro-5-oxo	-	4.16	-	4.56	-	2.80	1.41
1,3	Me	3.38
1	aDFucp4N	4.82	3.75	3.66	4.58	4.21	1.20
	Me	3.41


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7
1,4	xD3,4HO1,3MePro-5-oxo		72.3/4.16		76.6/4.56		30.5/2.80	22.0/1.41
1,3	Me	58.2/3.38
1	aDFucp4N	100.6/4.82	68.4/3.75	79.2/3.66	51.8/4.58	66.0/4.21	17.2/1.20
	Me	56.6/3.41

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CO[C@H]1O[C@H](C)[C@H](NC(=O)[C@@H]2N(C)C(=O)C(O)C2(C)O)[C@H](OC)[C@H]1O

362.379 g/mol (C₁₅H₂₆N₂O₈)

The lipopolysaccharide (LPS) O-antigen structure of the plant pathogen Rhizobium radiobacter strain TT9 and its possible role in a plant-microbe interaction was investigated. The analyses disclosed the presence of two O-antigens, named Poly1 and Poly2. The repetitive unit of Poly2 constitutes a 4-α-l-rhamnose linked to a 3-α-d-fucose residue. Surprisingly, Poly1 turned out to be a novel type of biopolymer in which the repeating unit is formed by a monosaccharide and an amino-acid derivative, so that the polymer has alternating glycosidic and amidic bonds joining the two units: 4-amino-4-deoxy-3-O-methyl-d-fucose and (2'R,3'R,4'S)-N-methyl-3',4'-dihydroxy-3'-methyl-5'-oxoproline). Differently from the O-antigens of LPSs from other pathogenic Gram-negative bacteria, these two O-antigens do not activate the oxidative burst, an early innate immune response in the model plant Arabidopsis thaliana, explaining at least in part the ability of this R. radiobacter strain to avoid host defenses during a plant infection process.

carbohydrates, structure elucidation, saccharides, structural biology, Biopolymers

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7
1,4	xD3,4HO1,3MePro-5-oxo	175.6	72.3	77.7	76.6	176.5	30.5	22.0
1,3	Me	58.2
1	bDFucp4N	105.3	71.0	82.5	51.5	71.3	17.2
	Me	58.8


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7
1,4	xD3,4HO1,3MePro-5-oxo	-	4.17	-	4.56	-	2.80	1.41
1,3	Me	3.38
1	bDFucp4N	4.35	3.41	3.53	4.57	3.93	1.23
	Me	3.58


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7
1,4	xD3,4HO1,3MePro-5-oxo		72.3/4.17		76.6/4.56		30.5/2.80	22.0/1.41
1,3	Me	58.2/3.38
1	bDFucp4N	105.3/4.35	71.0/3.41	82.5/3.53	51.5/4.57	71.3/3.93	17.2/1.23
	Me	58.8/3.58

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CO[C@H]1[C@@H](NC(=O)[C@@H]2N(C)C(=O)C(O)C2(C)O)[C@@H](C)O[C@@H](OC)[C@@H]1O

362.379 g/mol (C₁₅H₂₆N₂O₈)

The lipopolysaccharide (LPS) O-antigen structure of the plant pathogen Rhizobium radiobacter strain TT9 and its possible role in a plant-microbe interaction was investigated. The analyses disclosed the presence of two O-antigens, named Poly1 and Poly2. The repetitive unit of Poly2 constitutes a 4-α-l-rhamnose linked to a 3-α-d-fucose residue. Surprisingly, Poly1 turned out to be a novel type of biopolymer in which the repeating unit is formed by a monosaccharide and an amino-acid derivative, so that the polymer has alternating glycosidic and amidic bonds joining the two units: 4-amino-4-deoxy-3-O-methyl-d-fucose and (2'R,3'R,4'S)-N-methyl-3',4'-dihydroxy-3'-methyl-5'-oxoproline). Differently from the O-antigens of LPSs from other pathogenic Gram-negative bacteria, these two O-antigens do not activate the oxidative burst, an early innate immune response in the model plant Arabidopsis thaliana, explaining at least in part the ability of this R. radiobacter strain to avoid host defenses during a plant infection process.

carbohydrates, structure elucidation, saccharides, structural biology, Biopolymers

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
4	aDFucp4N	100.0	67.7	78.0	72.1	67.3	15.4
	aLRhap	102.3	70.9	69.2	81.1	68.6	17.2


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
4	aDFucp4N	5.06	3.95	3.93	3.91	4.42	1.22
	aLRhap	5.04	4.10	3.97	3.52	3.97	1.38


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
4	aDFucp4N	100.0/5.06	67.7/3.95	78.0/3.93	72.1/3.91	67.3/4.42	15.4/1.22
	aLRhap	102.3/5.04	70.9/4.10	69.2/3.97	81.1/3.52	68.6/3.97	17.2/1.38

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

[*]O[C@H]1[C@@H](N)[C@@H](C)O[C@H](O[C@H]2[C@H](C)O[C@@H]([*])[C@H](O)[C@@H]2O)[C@@H]1O

291.3 g/mol (C₁₂H₂₁R₂NO₇, R = next and previous repeats, not counted in mol weight)

The lipopolysaccharide (LPS) O-antigen structure of the plant pathogen Rhizobium radiobacter strain TT9 and its possible role in a plant-microbe interaction was investigated. The analyses disclosed the presence of two O-antigens, named Poly1 and Poly2. The repetitive unit of Poly2 constitutes a 4-α-l-rhamnose linked to a 3-α-d-fucose residue. Surprisingly, Poly1 turned out to be a novel type of biopolymer in which the repeating unit is formed by a monosaccharide and an amino-acid derivative, so that the polymer has alternating glycosidic and amidic bonds joining the two units: 4-amino-4-deoxy-3-O-methyl-d-fucose and (2'R,3'R,4'S)-N-methyl-3',4'-dihydroxy-3'-methyl-5'-oxoproline). Differently from the O-antigens of LPSs from other pathogenic Gram-negative bacteria, these two O-antigens do not activate the oxidative burst, an early innate immune response in the model plant Arabidopsis thaliana, explaining at least in part the ability of this R. radiobacter strain to avoid host defenses during a plant infection process.

carbohydrates, structure elucidation, saccharides, structural biology, Biopolymers

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7
4	xD3,4HO1,3MePro-5-oxo	173.8	72.5	77.8	80.0	173.8	30.4	22.1
3	Me	57.9
	aDFucp4N	99.9	68.6	78.5	51.6	66.6	17.0


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7
4	xD3,4HO1,3MePro-5-oxo	-	4.16	-	4.71	-	2.82	1.15
3	Me	3.42
	aDFucp4N	5.16	3.79	3.86	4.67	4.63	1.21


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7
4	xD3,4HO1,3MePro-5-oxo		72.5/4.16		80.0/4.71		30.4/2.82	22.1/1.15
3	Me	57.9/3.42
	aDFucp4N	99.9/5.16	68.6/3.79	78.5/3.86	51.6/4.67	66.6/4.63	17.0/1.21

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

[*]OC1C(=O)N(C)[C@@H](C(=O)N[C@@H]2[C@H](OC)[C@@H](O)[C@@H]([*])O[C@@H]2C)C1(C)O

330.337 g/mol (C₁₄H₂₂R₂N₂O₇, R = next and previous repeats, not counted in mol weight)