Accessory subunit of plasma membrane calcium-transporting ATPase ATP2B2/PMCA2 that stabilizes the transporter at the cell surface (By similarity). Also acts as a chaperone for ATP2B1; stabilizes ATP2B1 and increases its ATPase activity (PubMed:30190470). Probable homophilic and heterophilic cell adhesion molecule involved in long term potentiation at hippocampal excitatory synapses through activation of p38MAPK (By similarity). May also regulate neurite outgrowth by activating the FGFR1 signaling pathway (By similarity). May play a role in synaptic plasticity (By similarity). Promotes localization of XKR8 at the cell membrane (PubMed:27503893). {ECO:0000250|UniProtKB:P97300, ECO:0000250|UniProtKB:P97546, ECO:0000269|PubMed:27503893, ECO:0000269|PubMed:30190470}. This is the function of Ensembl gene identifier ENSG00000156642 (NPTN, neuroplastin).