Elton Zeqiraj and Beatrice Filippi publish spectacular structure of the LKB1 tumour suppressor complex
Much research in the MRC PPU over the last 11 years has focused on understanding the roles of the LKB1 tumour suppressor protein kinase, as loss of function mutations in this enzyme are frequently observed to promote cancer. Some progress has been made. It is now clear that LKB1 exerts its growth suppressing effects by activating a group of other ~14 kinases comprising AMPK and AMPK-related kinases. Activation of AMPK by LKB1 suppresses growth and proliferation when energy and nutrient levels are scarce. Activation of AMPK-related kinases by LKB1 plays vital roles maintaining cell polarity thereby inhibiting inappropriate expansion of tumour cells. A picture from current research is emerging that loss of LKB1 leads to disorganization of cell polarity and facilitates tumour growth under energetically unfavorable conditions.
A fascinating feature of LKB1 is that it is activated by an unusual allosteric mechanism involving interaction with an inactive pseudokinase termed STRAD and a scaffolding protein termed MO25. For the last 8 years in collaboration with Daan van Aalten's lab we have been attempting to crystallize this complex to understand the molecular mechanism by which LKB1 is activated. Elton courageously took up the challenge to crystallize LKB1 for his PhD project. For the first 3 years Elton encountered numerous obstacles in expressing and crystallizing LKB1 and it was suggested many times that he should find another simpler project to work on. However, Elton ignored these comments and persevered defying the odds by succeeding in crystallizing and solving the structure of the heterotrimeric LKB1:STRAD:MO25 complex. Click here to see a movie of the crystal structure of the heterotrimeric LKB1. (Pink): STRAD (green): MO25 (blue). Location of LKB1 residues mutated in cancer are shown in purple.
With the help of Maria Deak, Beatrice Filippi then analysed the effect that over 100 mutations in interesting regions of the LKB1 complex had on complex assembly and activity.
Together, these data provide a stunning picture of how LKB1 is activated. The pseudokinase STRAD despite being catalytically inactive binds ATP and adopts a closed conformation typical of active protein kinases. LKB1 interacts with STRAD as a pseudosubstrate. LKB1 is maintained in an active conformation by forming a web of interactions with both STRAD and MO25. The structure of the LKB1 complex also strikingly reveals how many mutations found in Peutz-Jeghers syndrome and other cancers impair LKB1 function.
The finding that STRAD despite being catalytically inactive, exerts its biological function by folding into an active conformation and binding LKB1 in the same manner as which an active kinase would interact with a substrate, is likely to be relevant to understanding the evolution and function of other poorly studied pseudokinases (of which there are ~30-50 encoded by the human genome).
Click here to read the paper describing the LKB1 heterotrimeric structure.
Elton has now completed his PhD and is departing to undertake postdoctoral research in one of Canada's pre-eminent scientists, Frank Sicheri's laboratory at the Samuel Lunenfeld Research institute. Beatrice is now investigating the docking mechanisms by which LKB1 interacts with its substrates.
A fascinating feature of LKB1 is that it is activated by an unusual allosteric mechanism involving interaction with an inactive pseudokinase termed STRAD and a scaffolding protein termed MO25. For the last 8 years in collaboration with Daan van Aalten's lab we have been attempting to crystallize this complex to understand the molecular mechanism by which LKB1 is activated. Elton courageously took up the challenge to crystallize LKB1 for his PhD project. For the first 3 years Elton encountered numerous obstacles in expressing and crystallizing LKB1 and it was suggested many times that he should find another simpler project to work on. However, Elton ignored these comments and persevered defying the odds by succeeding in crystallizing and solving the structure of the heterotrimeric LKB1:STRAD:MO25 complex. Click here to see a movie of the crystal structure of the heterotrimeric LKB1. (Pink): STRAD (green): MO25 (blue). Location of LKB1 residues mutated in cancer are shown in purple.
With the help of Maria Deak, Beatrice Filippi then analysed the effect that over 100 mutations in interesting regions of the LKB1 complex had on complex assembly and activity.
Together, these data provide a stunning picture of how LKB1 is activated. The pseudokinase STRAD despite being catalytically inactive binds ATP and adopts a closed conformation typical of active protein kinases. LKB1 interacts with STRAD as a pseudosubstrate. LKB1 is maintained in an active conformation by forming a web of interactions with both STRAD and MO25. The structure of the LKB1 complex also strikingly reveals how many mutations found in Peutz-Jeghers syndrome and other cancers impair LKB1 function.
The finding that STRAD despite being catalytically inactive, exerts its biological function by folding into an active conformation and binding LKB1 in the same manner as which an active kinase would interact with a substrate, is likely to be relevant to understanding the evolution and function of other poorly studied pseudokinases (of which there are ~30-50 encoded by the human genome).
Click here to read the paper describing the LKB1 heterotrimeric structure.
Elton has now completed his PhD and is departing to undertake postdoctoral research in one of Canada's pre-eminent scientists, Frank Sicheri's laboratory at the Samuel Lunenfeld Research institute. Beatrice is now investigating the docking mechanisms by which LKB1 interacts with its substrates.