Subcellular localization of adenosine kinase in mammalian cells: The long isoform of AdK is localized in the nucleus |
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Authors: | Xianying Amy Cui |
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Affiliation: | Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ont., Canada L8N3Z5 |
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Abstract: | Two isoforms of adenosine kinase (AdK) have been identified in mammalian organisms with the long isoform (AdK-long) containing extra 20-21 amino acids at the N-terminus (NTS). The subcellular localizations of these isoforms are not known and they contain no identifiable targeting sequence. Immunofluorescence labeling of mammalian cells expressing either only AdK-long or both isoforms with AdK-specific antibody showed only nuclear labeling or both nucleus and cytoplasmic labeling, respectively. The AdK-long and -short isoforms fused at the C-terminus with c-myc epitope also localized in the nucleus and cytoplasm, respectively. Fusion of the AdK-long NTS to green fluorescent protein also resulted in its nuclear localization. AdK-long NTS contains a cluster of conserved amino acids (PKPKKLKVE). Replacement of KK in this sequence with either AA or AD abolished its nuclear localization capability, indicating that this cluster likely serves as a nuclear localization signal. AdK in nucleus is likely required for sustaining methylation reactions. |
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Keywords: | Adenosine kinase Enzyme isoforms Subcellular localization Purine salvage pathway Nuclear localization sequence Methylation reactions |
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