Methylation of the DNA/RNA-binding protein Kin17 by METTL22 affects its association with chromatin.

Kin17 is a protein that was discovered through its immunoreactivity towards an antibody directed against prokaryotic RecA. Further study of Kin17 revealed a function in DNA replication and repair, as well as in pre-mRNA processing. Recently, it was found that Kin17 is methylated on lysine 135 by the newly discovered methyltransferase METTL22. To better understand the function of Kin17 and its regulation by methylation, we used multiple cell compartment protein affinity purification coupled with mass spectrometry (MCC-AP-MS) to identify novel interaction partners of Kin17 and to assess whether these interactions can take place on chromatin. Our results confirm that Kin17 interacts with METTL22 both in the soluble and chromatin fractions. We also show that many RNA-binding proteins, including the previously identified interactor BUD13 as well as spliceosomal and ribosomal subunits, associate with Kin17 in the soluble fraction. Interestingly, overexpression of METTL22 in HEK 293 cells displaces Kin17 from the chromatin to the cytoplasmic fraction, suggesting a role for methylation of lysine 135, a residue that lies within a winged helix domain of Kin17, in regulating association with chromatin. These results are discussed in view of the putative cellular function of Kin17. BIOLOGICAL SIGNIFICANCE: The results shown here broaden our understanding of METTL22, a member of a family of newly-discovered non-histone lysine methyltransferases and its substrate, Kin17, a DNA/RNA-binding protein with reported roles in DNA repair and replication and mRNA processing. An innovative method to study protein-protein interactions in multiple cell compartments is employed to outline the interaction network of both proteins. Functional experiments uncover a correlative role between Kin17 lysine methylation and its association with chromatin. This article is part of a Special Issue entitled: Can Proteomics Fill the Gap Between Genomics and Phenotypes?