SMN2 and proximal spinal muscular atrophy: Taken together, it is conceivable that the buried side chains of SMN’s Asp44 and Gemin2’s Arg213 form a salt bridge, which constitutes a favourable electrostatic energy contribution to the SMN-Gemin2 complex structural stability [27], and highlights the functionally indispensable roles of the two residues’ charged side chains, considering the experimental observation that the SMN-Gemin2 binding is abrogated by the D44V mutation [27], resulting in a functionally deficient SMA-linked D44V SMN mutant (SMND44V).