The protein p42IP4 (aka Centaurin α-1) is highly enriched in the brain and has specific binding sites for the membrane lipid phosphatidylinositol 3,4,5-trisphosphate and the soluble messenger inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4,5)P4; IP4). p42IP4 shuttles between plasma membrane, cytosol and cell nucleus. However, the molecular function of p42IP4 is still largely unclear. Here, we report a novel interaction partner for p42IP4, Ran binding protein in microtubule-organizing center (RanBPM). RanBPM is ubiquitously expressed and seems to act as scaffolding and modulator protein. In our studies, we established this interaction in vitro and in vivo. The in vivo interaction was demonstrated with endogenous RanBPM from rat brain. Both proteins co-localize in transfected HEK 293 cells. We could show that the interaction does not require additional proteins. D-Ins(1,3,4,5)P4, a specific ligand for p42IP4, is a concentration-dependent and stereoselective inhibitor of this interaction; the L-isoform is much less effective. We found that mainly the SPRY domain of RanBPM mediates the p42IP4-RanBPM association. The ARFGAP domain of p42IP4 is important for the interaction, without being the only interaction site. Recently, p42IP4 and RanBPM were shown to be involved in dendritic differentiation. Thus, we hypothesize that RanBPM could act as a modulator together with p42IP4 in synaptic plasticity.