Insights into the structural dynamics of Liver kinase B1 (LKB1) by the binding of STe20 Related Adapterα (STRADα) and Mouse protein 25α (MO25α) co-activators

Abstract

LKB1, the tumour suppressor, is found mutated in Peutz-Jeghers syndrome (PJS). The LKB1 is a serine-threonine kinase protein that is allosterically activated by the binding of STRADα and MO25α without phosphorylating the Thr212 present at activation loop. The present study aims to highlight the structural dynamics and complexation mechanism during the allosteric activation of LKB1 by these co-activators using molecular dynamics simulations. The all atom simulations performed on the complexes of LKB1 with ATP, STRADα, and MO25α for a period of 30 ns reveal that binding of STRADα and MO25α significantly stabilizes the highly flexible regions of LKB1 such as ATP binding region (β1-β2 loop), catalytic & activation loop segments and αG helix. Also, binding of STRADα and MO25α to LKB1 promotes coordinated motion between N- and C-lobes along with the catalytic & activation loops by forming H-bonds between LKB1 and co-activators, which further facilitate to establish the conserved attributes of active LKB1 such as (i) formation of salt bridge between Lys78 and Glu98, (ii) formation of stable hydrophobic R- and C-spines, and (iii) interaction between both catalytic and activation loops. Especially, the residues of LKB1 interacting with STRADα (Arg74, Glu342) and MO25α (Glu165, Pro203 and Phe204) are observed to play a significant role in stabilizing the (LKB1-ATP)-(STRADα-ATP)-MO25α complex. Overall, the present work highlighting the structural dynamics of LKB1 by the binding of allosteric co-activators is expected to provide a basic understanding on drug design specific to PJS syndrome.