title: Nuclear targeting of methyl-recycling enzymes in Arabidopsis thaliana is mediated by specific protein interactions.
abstract: Numerous transmethylation reactions are required for normal plant growth and development. S-adenosylhomocysteine hydrolase (SAHH) and adenosine kinase (ADK) act coordinately to recycle the by-product of these reactions, S-adenosylhomocysteine (SAH) that would otherwise competitively inhibit methyltransferase (MT) activities. Here, we report on investigations to understand how the SAH produced in the nucleus is metabolized by SAHH and ADK. Localization analyses using green fluorescent fusion proteins demonstrated that both enzymes are capable of localizing to the cytoplasm and the nucleus, although no obvious nuclear localization signal was found in their sequences. Deletion analysis revealed that a 41-amino-acid segment of SAHH (Gly(150)-Lys(190)) is required for nuclear targeting of this enzyme. This segment is surface exposed, shows unique sequence conservation patterns in plant SAHHs, and possesses additional features of protein-protein interaction motifs. ADK and SAHH interact in Arabidopsis via this segment and also interact with an mRNA cap MT. We propose that the targeting of this complex is directed by the nuclear localization signal of the MT; other MTs may similarly target SAHH/ADK to other subcellular compartments to ensure uninterrupted transmethylation.
authors: Department of Biology, University of Waterloo, Waterloo, ON, N2L 3G1, Canada.
authors: Sanghyun
authors: S
authors: Lee
authors: Andrew C
authors: AC
authors: Doxey
authors: Brendan J
authors: BJ
authors: McConkey
authors: Barbara A
authors: BA
authors: Moffatt
mesh_terms: D043383:Adenosylhomocysteinase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D008780:Methyltransferases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport; D011505:Protein-Tyrosine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012315:RNA Caps / Q000235:genetics / Q000378:metabolism; D012435:S-Adenosylhomocysteine / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D019913:Nuclear Localization Signals; D012315:RNA Caps; D012435:S-Adenosylhomocysteine; D008780:Methyltransferases; C090910:ADK1 protein, Arabidopsis; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D043383:Adenosylhomocysteinase