Abstract: Interactions of lanthanide ions with Ca2+/calmodulin(CaM) signal transduction is a crucial pathway for the biological effect of lanthanides. In the present work, the effect of La3+ on binding of CaM to its binding proteins(CaMBP) was investigated by an immobilized CaM affinity chromatographic method in rat’s brain homogenate. CaMBP binding to La3+-activated CaM gel were analyzed by SDS-PAGE and some CaMBP were identified by MALDI-TOF-MS. The concentration dependency on La3+ for CaM-CaMBP binding was determined in a mimetic cellular media and compared with that of Ca2+. The experimental results showed that (1) the CaMBP species activated by La3+ were primarily the same as those of Ca2+. Five selected CaMBP were identified to be 6-phosphofructokinase(PFK), glyceraldehyde-3-phosphate dehydrogenase(GAPDH)(enzymes in glycolysis), tubulin, actin(cytoskeleton proteins), and heat shock cognate 71000 protein(HSCP71, stress chaperone), indicating that La3+ may interfere with multiple cellular processes through CaM. (2) The effective concentrations for La3+ to induce binding of CaM to CaMBP depended on CaMBP species. Tubulin, actin and HSCP71 were observed to be sensitive to La3+ revealed by the affinity constants K of La3+ to CaM in the metal-CaM-CaMBP tertiary system, which are similar or higher than those of Ca2+. However, in the systems with PFK or GAPDH, La3+ bound to CaM less tightly. We hypothesized that this may attribute to complexity of mimetic cellular media and/or the effects of CaM-CaMBP interaction on CaM-metal binding, on which further studies should be appropriate. The work may offer new insight to the mechanisms of the biological effects of lanthanides.

Key words: Calmodulin, Calmodulin binding protein, Lanthanide, Proteomics