Mass Spectrometry

Biography

Biography: Dijana Matak-Vinković

Abstract

CK2 is an intrinsically active protein kinase that is crucial for cellular viability and exists as a heterotetrameric holoenzyme (α₂/β₂) composed of two catalytic α subunits (denoted as CK2α or α) attached to a central, regulatory dimer of β subunits (denoted as CK2β or β₂). However, conventional kinase regulatory mechanisms do not apply to CK2, and its mode of regulation remains elusive. Interestingly, CK2 is known to undergo reversible ionic-strength-dependent oligomerization. Furthermore, a regulatory mechanism based on autoinhibitory oligomerization, driven by the inter-holoenzyme electrostatic interactions between the acidic loop of CK2β and the basic substrate-binding regions of CK2α, has been postulated based on the observation of circular trimeric oligomers and linear CK2 assemblies in various crystal structures. Here, native mass spectrometry (MS) was employed to monitor the assembly of oligomeric CK2 species in an ionic-strength-dependent manner. Subsequently, ion mobility spectrometry-MS (IMS-MS) was used to examine the conformational state of the CK2 oligomers. To validate the findings from IMS-MS, hydrogen−deuterium exchange mass spectrometry (HDX-MS) was used to analyze the solution-phase conformation of CK2 oligomers. Through the use of a suite of orthogonal mass spectrometric techniques (native MS, IMS-MS and HDX-MS), it was shown that CK2 undergoes ionic-strength dependent oligomerization to form both circular and linear supramolecular assemblies, thus representing a novel mechanism of regulation for protein kinases. The results were consistent with previously proposed models of CK2 oligomerization derived from X-ray crystallographic analysis and in vivo evidence of CK2 aggregation.