Journal
JOURNAL OF STRUCTURAL BIOLOGY
Volume 200, Issue 1, Pages 36-44Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jsb.2017.08.006
Keywords
Lipid; Kinase; PI4KB; 14-3-3 protein; Phosphatidylinositol; Small-angle X-ray scattering (SAXS); GIN; Analytical ultracentrifugation; Structure; Proteolytical degradation
Funding
- Czech Science Foundation [17-05200S]
- National Science Centre, Poland [2016/21/B/NZ1/00006]
- Academy of Sciences of Czech Republic (RVO) [61388963]
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Phosphatidylinositol 4-kinase III beta (PI4KB) is responsible for the synthesis of the Golgi and trans-Golgi network (TGN) pool of phosphatidylinositol 4-phospahte (PI4P). PI4P is the defining lipid hallmark of Golgi and TGN and also serves as a signaling lipid and as a precursor for higher phosphoinositides. In addition, PI4KB is hijacked by many single stranded plus RNA (+RNA) viruses to generate PI4P-rich membranes that serve as viral replication organelles. Given the importance of this enzyme in cells, it has to be regulated. 14-3-3 proteins bind PI4KB upon its phosphorylation by protein kinase D, however, the structural basis of PI4KB recognition by 14-3-3 proteins is unknown. Here, we characterized the PI4KB:14-3-3 protein complex biophysically and structurally. We discovered that the PI4KB:14-3-3 protein complex is tight and is formed with 2:2 stoichiometry. Surprisingly, the enzymatic activity of PI4KB is not directly modulated by 14-3-3 proteins. However, 14-3-3 proteins protect PI4KB from proteolytic degradation in vitro. Our structural analysis revealed that the PI4KB:14-3-3 protein complex is flexible but mostly within the disordered regions connecting the 14-3-3 binding site of the PI4KB with the rest of the PI4KB enzyme. It also predicted no direct modulation of PI4KB enzymatic activity by 14-3-3 proteins and that 14-3-3 binding will not interfere with PI4KB recruitment to the membrane by the ACBD3 protein. In addition, the structural analysis explains the observed protection from degradation; it revealed that several disordered regions of PI4KB become protected from proteolytical degradation upon 14-3-3 binding. All the structural predictions were subsequently biochemically validated.s
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