Bioinformatical View on the Contribution of MAST/IRE-Dependent Phosphorylation in the Tubulin Code

Abstract

Protein kinases represent one of the largest eukaryotic enzyme superfamilies. However, only a few can directly phosphorylate tubulin and contribute to the modulation of the “tubulin code.” The authors previously confirmed the structural and functional homology of the plant protein kinase IREH1 and members of the mammalian MAST kinase family. Their participation in the regulation of the microtubule system in plant and animal cells was also experimentally confirmed. At the same time, the direct contribution of MAST/IRE to the “tubulin code” remains unclear. In the current study, based on bioinformatical and structural biology methods, the possibility of such an interaction was evaluated. The target sites of MAST/IRE-phosphorylation of tubulin were predicted based on similarity to the generalized specific profiles. Two potential MAST/IRE specific sites, conserved in human and Arabidopsis tubulins were selected: Thr73 (80) exists in most isotypes of α-tubulin and Ser115 was found in the majority of human and plant isotypes of β-tubulin. It was predicted that phosphorylation of the first site can affect the assembly of α/β-tubulin heterodimer, and phosphorylation of the second may affect the interaction between neighboring protofilaments of microtubules. The last site Ser433, was found in both γ-tubulin isotypes of A. thaliana, but it was absent in mammals. The external position of Ser433 in plant γ-tubulin allows for suggesting that phosphorylation of this amino acid can affect the structure of the γTuRC complex but it does not affect inner contacts of γTuSC and their interaction in the ring.