Spine-Associated RapGAP (SPAR) interacts with a PDZ-LIM domain family protein called PDZ and LIM domain 5 (PDLIM5), formerly known as Enigma Homolog (ENH). PDLIM5 is expressed postsynaptically in excitatory pyramidal neurons of the hippocampus and associates with SPAR protein in the brain. In hippocampal neurons, PDLIM5 promotes decreased dendritic spine size, opposite to the effect of SPAR overexpression that causes spine head enlargement.
Single nucleotide polymorphisms in PDLIM5 have been associated with schizophrenia, depression, and bipolar disorder (Kato et al. 2005, Li et al. 2008, Liu et al. 2008), although the physiological functions of PDLIM5 are not well understood.