Phosphorylation of Maize and Arabidopsis HMGB Proteins by Protein Kinase CK2α

• Published in: Biochemistry (Easton) Vol. 42; no. 12; pp. 3503 - 3508
• Main Authors: Stemmer, Christian, Leeming, Diana J, Franssen, Lars, Grimm, Rudi, Grasser, Klaus D
• Format: Journal Article
• Language: English
• Published: American Chemical Society 01.04.2003
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi027350d

In plants, a variety of chromatin-associated high mobility group (HMG) proteins belonging to the HMGB family have been identified. We have examined the phosphorylation of the HMGB proteins from the monocotyledonous plant maize and the dicotyledonous plant Arabidopsis by protein kinase CK2α. Maize CK2α phosphorylates the maize HMGB1 and HMGB2/3 proteins and the Arabidopsis HMGB1, HMGB2/3, and HMGB4 proteins. Maize HMGB4 and HMGB5 and Arabidopsis HMGB5 are not phosphorylated by CK2α. Depending on the HMGB protein up to five amino acid residues are phosphorylated in the course of the phosphorylation reaction. The HMGB1 proteins from both plants are markedly more slowly phosphorylated by CK2α than the other HMGB substrate proteins, indicating that certain HMGB proteins are clearly preferred substrates for CK2α. The rate of the phosphorylation reaction appears to be related to the ease of interaction between CK2α and the HMGB proteins, as indicated by chemical cross-linking experiments. MALDI/TOF mass spectrometry analyses demonstrate that the HMGB1 and HMGB2/3 proteins occur in various phosphorylation states in immature maize kernels. Thus, HMGB1 exists as monophosphorylated, double-phosphorylated, triple-phosphorylated, and tetraphosphorylated protein in kernel tissue, and the tetraphosphorylated form is the most abundant version. The observed in vivo phosphorylation states indicate that protein kinase(s) other than CK2α contribute(s) to the modification of the plant HMGB proteins. The fact that the HMGB proteins are phosphorylated to various extents reveals that the existence of differentially modified forms increases the number of distinct HMGB protein variants in plant chromatin that may be adapted to certain functions.