Substrate preference of 5′-methylthioadenosine/ S-adenosylhomocysteine nucleosidase in Burkholderia thailandensis.

5′-Methylthioadenosine/ S-adenosylhomocysteine nucleosidase ( MTAN) plays crucial roles in the production of autoinducers and methionine metabolism. Putative genes encoding MTAN and Ado Hcyase from Burkholderia thailandensis were cloned and characterized. The Km values of MTAN for 5′-methylthioadenosine ( MTA) and S-adenosylhomocysteine ( SAH) were 19 and 58 μM, respectively. The catalytic efficiency of MTAN for SAH was only 0.004% of the value for MTA, indicating an almost complete substrate preference of MTAN for MTA. The results of autoinducer-2 assay of B. thailandensis and recombinants indicated that LuxS enzyme activity was lacking in Burkholderia species. Instead, Ado Hcyase hydrolysed SAH directly to homocysteine and adenosine in the activated methyl cycle. Meanwhile, the Km value of Ado Hcyase for SAH was determined to be 40 μM. Sequence analysis revealed that MTAN had much higher diversity than Ado Hcyase, which likely contributes to its substrate preference for MTA. Furthermore, the phylogenetic tree of MTAN sequences revealed that LuxS+ bacteria could be discriminated from LuxS− bacteria. These results suggested that the substrate preference of MTAN for MTA and SAH degradation pathway evolved with the bacterial-activated methyl cycle. [ABSTRACT FROM AUTHOR]