AKINbeta3, a plant specific SnRK1 protein, is lacking domains present in yeast and mammals non-catalytic ?-subunits
Résumé
The SNF1/AMPK/SnRK1 heterotrimeric kinase complex is involved in the adaptation of cellular metabolism in response to diverse stresses in yeast, mammals and plants. Following a model proposed in yeast, the kinase targets are likely to bind the complex via the non-catalytic β-subunits. These proteins currently identified in yeast, mammals and plants present a common structure with two conserved interacting domains named Kinase Interacting Sequence (KIS) and Association with SNF1 Complex (ASC), and a highly variable N-terminal domain. In this paper we describe the characterisation of AKINβ3, a novel protein related to AKINβ subunits of Arabidopsis thaliana, containing a truncated KIS domain and no N-terminal extension. Interestingly the missing region of the KIS domain corresponds to the glycogen-binding domain (β-GBD) identified in the mammalian AMPKβ1. In spite of its unusual features, AKINβ3 complements the yeast sip1Δsip2Δgal83Δ mutant. Moreover, interactions between AKINβ3 and other AKIN complex subunits from A. thaliana were detected by two-hybrid experiments and in vitro binding assays. Taken together these data demonstrate that AKINβ3 is a β-type subunit. A search for β-type subunits revealed the existence of β3-type proteins in other plant species. Furthermore, we suggest that the AKINβ3-type subunits could be plant specific since no related sequences have been found in any of the other completely sequenced genomes. These data suggest the existence of novel SnRK1 complexes including AKINβ3-type subunits, involved in several functions among which some could be plant specific.