User:Marcin Jozef Suskiewicz/Sandbox MarcinSuskiewicz
From Proteopedia
NodS is a bacterial methyltransferase involved in the pathway leading to the biosynthesis of Nod factor, an important signaling molecule released by rhizobial bacteria in the course of endosymbiotic interaction with legumes. It is the first S-adenosyl-L-methionine-dependent methyltransferase specific for chitooligosaccharide substrates, the structure of which has been solved, with (3ofk) and without (3ofj) S-adenosyl-L-homocysteine ligand.[1][2]
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Biological significance
Rhizobia-legumes symbiosis
The endosymbiotic relationship between nitrogen-fixing rhizobial bacteria and certain plants (legumes) is of the utmost importance for the nitrogen cycle in the biosphere and hence an object of intense study by specialists from various areas of biology. What is more, although the use of artificial nitrogen-containing fertilizers made it possible to bypass the strict dependence on this process, its understanding is still crucial for the efficient agriculture. Biological nitrogen fixation requires nitrogenase, an enzyme present in, among others, rhizobial bacteria but absent in plants. The rhizobia are a diverse range of soil bacteria. It is thought that after the symbiotic capabilities were first acquired by some of them, they spread by means of horizontal transfer of a plasmid or genomic island containing genes important for the process. The symbiotic relationship between the two symbionts depends on the formation of invasion structures (nodules) by the host, allowing bacteria to enter the plant root, colonize a specific type of cells and be transformed into bacteroids which perform nitrogen fixation. As complementarity between various signals and their cognate receptors is required for the efficient symbiosis, its emergence most likely required coevolution of plants and bacteria.[3][4] One of the bacterial nodulating symbionts is Bradyrhizobium japonicum WM9, which is involved in a partnership with lupine and serradella legumes.[5]
Chemical signals
The very first stage of this process is an exchange of chemical signals between the symbionts. On sensing a flavonoid compound released by the plant, the bacteria produce a signalling molecule known as Nod factor, which is a lipochitooligosaccharide derivative. This molecule in turn induces nodule formation by the plant.[6][7][8] Many types of flavonoids and Nod factors are known and which ones are present influences the specificity of the interaction. It must be mentioned that while these two molecules are important signals and specificity determinants, there are numerous others.[9][10]
Nod factor synthesis
Nod factor synthesis involves the coordinated action of several rhizobial enzymes encoded by the nodulation-specific genes. NodC, NodB and NodA, found in nearly all rhizobial strains, synthesize the main part of Nod factor's structure, while several others, including NodS, NodU, NolO, NodL, and NolL, introduce species- and strain-specific modifications, such as N-methylation, carbamoylation, acetylation, fucosylation etc.[11][12]
The structure and activity of NodS
NodS is an S-adenosyl-L-methionine (SAM)-dependent methyltransferase that methylates the deacetylated nitrogen atom at the nonreducing end of the chitooligosaccharide substrate, converting at the same time the S-adenosyl-L-methionine methyl donor into S-adenosyl-L-homocysteine, which is then released as a by-product.[13] S-adenosyl-L-methionine-dependent methyltransferases, many of which have been reported to date, methylate a wide variety of substrates and are involved in diverse processes ranging from biosynthetic pathways to gene silencing. Those of them which have been structurally analyzed have been divided into five structural families known as classes I–V, class I, to which NodS belongs, being the most numerous.[14] Its typical fold consists of a seven-stranded β-sheet with a reversed β-hairpin at the C-terminal end of the sheet. The sheet is surrounded on both sides by α-helices, forming an α/β/α folding pattern.
