Exploring Obscurin and SPEG Kinase Biology.

Jennifer R Fleming,Stephan Lange,Jamie Kraft,Emma Börgeson,Alankrita Rani,Sanja Zenker

doi:10.3390/jcm10050984

Abstract

Three members of the obscurin protein family that contain tandem kinase domains with important signaling functions for cardiac and striated muscles are the giant protein obscurin, its obscurin-associated kinase splice isoform, and the striated muscle enriched protein kinase (SPEG). While there is increasing evidence for the specific roles that each individual kinase domain plays in cross-striated muscles, their biology and regulation remains enigmatic. Our present study focuses on kinase domain 1 and the adjacent low sequence complexity inter-kinase domain linker in obscurin and SPEG. Using Phos-tag gels, we show that the linker in obscurin contains several phosphorylation sites, while the same region in SPEG remained unphosphorylated. Our homology modeling, mutational analysis and molecular docking demonstrate that kinase 1 in obscurin harbors all key amino acids important for its catalytic function and that actions of this domain result in autophosphorylation of the protein. Our bioinformatics analyses also assign a list of putative substrates for kinase domain 1 in obscurin and SPEG, based on the known and our newly proposed phosphorylation sites in muscle proteins, including obscurin itself.

Highlights

This tandem kinase domain architecture is found in SPEG—containing the kinase domains SK1 and SK2, which are homologous to kinase domains found in obscurin [7]
It remains undetermined which of the two kinase domains within SPEG is responsible for this catalytic activity
We wondered if SPEG or the highly homologous obscurin contain putative phosphorylation sites that are similar to SPEGs phosphorylation site within RyR2

Summary

Introduction

The obscurin protein family consists of three members: the giant protein obscurin with its three main splice isoforms The giant obscurin isoforms contain a calcium/calmodulin-binding IQ-motif and RhoGEF domain triplet (consisting of serially linked SH3-DH-PH domains). ObscurinB has an additional two C-terminally located kinase domains (OK1 and OK2), which are present in the obscurin-associated kinase isoform [2,6,10]. This tandem kinase domain architecture is found in SPEG—containing the kinase domains SK1 and SK2, which are homologous to kinase domains found in obscurin [7]

Methods

Results

Conclusion