Spotlights
I want to break free
The regulation of protein kinase activity by activation loop phosphorylation is a well-characterized mechanism. Protein kinases that auto-phosphorylate usually do so in trans: dimerization results in reciprocal phosphorylation of the activation loop by the other protomer. However, we have discovered that Protein Kinase D (PKD) has evolved the inverse solution to the same problem. PKD is an inactive dimer that is activated by kinase domain dissociation followed by cis-autophosphorylation (Reinhardt et al, PNAS, 2023).
Made to measure
The myotonic dystrophy kinases of the DMPK family are conserved regulators of actomyosin contractility. The four prototypical DMPK members are obligate homodimers with a conserved architecture of N-terminal kinase domains, a central coiled-coil, and C-terminal membrane binding domains. Remarkably, the length of the coiled-coil domain of each family member varies between 10 and 145 nm, but is astonishingly well conserved. We present a model in which the activity of these kinases is regulated by their spatial positioning with respect to the membrane (Truebestein et al, Structure, 2023).
Brothers in Arms
Phosphoinositide-dependent kinase 1 (PDK1) is an essential protein kinase that controls cellular and organismal growth. We have elucidated the mechanism by which PDK1 is activated by phosphatidylinositol-3,4,5-trisphosphate (PIP3) at the plasma membrane in response to growth factor-mediated activation of cell surface receptors. Our work reveals previously unknown mechanisms of autoinhibition and trans-autoactivation, with opportunities for the development of novel therapeutics in the treatment of cancer (Levina et al, Nature Communications, 2022).
© Illustration by Dorotea Fracchiolla (Art&Science)
The final Akt
The lipid second messengers PI(3,4,5)P3 and PI(3,4)P2 have long been known to activate Akt by recruiting it to membranes, where it is activated by phosphorylation. We have determined the structure of autoinhibited Akt1, revealing the molecular basis of a disease-causing mutation in the PH domain which gives rise to Proteus Syndrome and some cancers. Phosphorylation is insufficient to fully activate Akt1. Our work implies that Akt signaling is restricted to discrete membrane locations in the cell (Truebestein et al, PNAS, 2021).
An intracellular zip code for kinase activity
Serum- and glucocorticoid-regulated kinase 3 (Sgk3) is activated by the phospholipid phosphatidylinsoitol 3-phosphate (PI3P) in the PI3 kinase pathway. Up-regulation of Sgk3 activity has increasingly been implicated in cancers that exhibit paradoxically low Akt activity. We have discovered that Sgk3 is dependent on PI3P for its activity, which restricts its activity to PI3P-rich endosomes in cells. We have biochemically reconstituted Sgk3 activation downstream of the class III PI 3-kinase Vps34 in vitro (Pokorny et al, Journal of Biological Chemistry, 2021).
It takes two to tango
Protein Kinase D (PKD) is an essential ser/thr kinase involved in vesicular transport of cargo from the trans-Golgi network to the plasma membrane. We have discovered a novel, ubiquitin-like domain in PKD that mediates its dimerization on diacylglycerol-containing membranes, thereby driving trans-autophosphorylation and activation of its kinase domain (Elsner et al, Journal of Biological Chemistry, 2019).
Location, location, location
The protein kinase Akt integrates signals from membrane-embedded lipid second messengers and signals in the form of phosphorylation by upstream protein kinases. We have shown that one without the other is insufficient for Akt activation and that membrane dissociation triggers rapid dephosphorylation and inactivation of Akt (Lučić et al, PNAS, 2018).
Akt-ing up in cancer
We recently demonstrated that the activity of a protein kinase called Akt, which promotes cell growth and proliferation, is strictly governed by the engagement of two specific lipids in cell membranes (Ebner & Lučić et al, Molecular Cell, 2017). Bypassing this requirement leads to uncontrolled growth and cancer.
Switching off with ADP
We have discovered an allosteric switch in the Src and Tec kinases that converts them into active enzymes by promoting the exchange of ADP for ATP (von Raußendorf et al, Scientific Reports, 2017). The switch depends on recognition of a polyproline motif in the tail of activated receptors at the plasma membrane.
Bridging the gap
Rho-associated coiled-coil kinase (ROCK) is a key signal transducer in regulating the cytoskeleton. Substrate engagement is controlled by the precise positioning of its kinase domains, which is achieved via a long coiled-coil domain that bridges its membrane binding domains to its kinase domains (Truebestein et al., Nature Communications, 2016).
11:00
IMBA/GMI Lecture Hall
Dea Slade
Gaia Novarino