Modulates calcium-dependent activity of inositol 1,4,5-triphosphate receptors (ITPRs)(PubMed:14570872). Inhibits agonist-induced intracellular calcium signaling (PubMed:15980432). Enhances inactivation and does not support calcium-dependent facilitation of voltage-dependent P/Q-type calcium channels (PubMed:11865310). Causes calcium-dependent facilitation and inhibits inactivation of L-type calcium channels by binding to the same sites as calmodulin in the C-terminal domain of CACNA1C, but has an opposite effect on channel function (PubMed:15140941). Suppresses the calcium-dependent inactivation of CACNA1D (By similarity). Inhibits TRPC5 channels (PubMed:15895247). Prevents NMDA receptor-induced cellular degeneration. Required for the normal transfer of light signals through the retina (By similarity). Homodimer; when bound to calcium or magnesium. Interacts (via C-terminus) with ITPR1, ITPR2 and ITPR3. This binding is calcium dependent and the interaction correlates with calcium concentration. An additional calcium-independent interaction with the N-terminus of ITPR1 results in a decreased InsP(3) binding to the receptor. Interacts with CACNA1A (via C-terminal CDB motif) in the pre- and postsynaptic membranes. Interacts with CACNA1C (via C-terminal C and IQ motifs). The binding to the C motif is calcium independent whereas the binding to IQ requires the presence of calcium and is mutually exclusive with calmodulin binding. Interacts with CACNA1D (By similarity). Interacts with TRPC5 (via C-terminus). Interacts (via EF-hands 1 and 2) at microtubules with MAP1LC3B. Interacts with MYO1C (By similarity). Interacts (via EF-hands 1 and 2) with NSMF (via the central NLS-containing motif region), the interaction occurs in a calcium dependent manner after synaptic NMDA receptor stimulation and prevents nuclear import of NSMF. Interacts with SPACA9 (By similarity). L-CaBP1 is associated most likely with the cytoskeletal structures, whereas S-CaBP1 is localized at or near the plasma membrane. L-CaBP1 is associated most likely with the cytoskeletal structures. S-CaBP1 is localized at or near the plasma membrane. Experimental confirmation may be lacking for some isoforms. Retina and brain. Somatodendritic compartment of neurons. Calbrain was found exclusively in brain where it is abundant in the hippocampus, habenular area in the epithalamus and in the cerebellum. EF-1 binds magnesium constitutively under physiological conditions, EF-3 and EF-4 bind calcium cooperatively and EF-2 binds neither calcium nor magnesium. Phosphorylated. The phosphorylation regulates the activity. It is currently uncertain whether calbrain represent a spliced isoform. The interaction with CACNA1A is described as calcium independent in PubMed:11865310 while it is shown to be acutely calcium dependent in PubMed:14570872. PubMed:12032348 describes a stimulatory effect of CABP1 during agonist-induced intracellular calcium signaling while PubMed:14570872 and PubMed:11865310 show an inhibitory effect.