Structural and functional characterization of annexin 1 from Medicago truncatula

Annexins are calcium- and membrane-binding proteins that have been shown to have diverse properties such as actin, integrin and GTP binding, both in animals and plants. Recently, Medicago truncatula annexin 1 (AnnMt1) has been suggested to participate in nodulation (Nod factor signaling) and mycorrhization in legume plants. In this report we demonstrate for the first time that recombinant AnnMt1 (rec-AnnMt1) mediates membrane permeabilization to cations with conductance ranging from 16 pS to 329 pS. In agreement with other structurally determined annexins, homology modeling of AnnMt1 suggests that most of the functional determinants are found on the convex surface of the modeled structure. In conclusion, we propose a potential constitutive role of AnnMt1 in Nod factor signaling as a non-specific ion channel.