Human Ca2+ receptor cysteine-rich domain - Analysis of function of mutant and chimeric receptors

The 612-residue extracellular domain of the human Ca2+ receptor (hCaR) has been speculated to consist of a Venus's-flytrap domain (VFT) and a cysteine -rich domain. We studied the function of the hCaR Cys-rich domain by using mutagenesis and chimera approaches. A chimeric hCaR with the sequence from residues 540-601 replaced by the corresponding sequence from the Fugu CaR r emained fully functional. Another chimeric hCaR with the same region of seq uence replaced by the corresponding sequence from metabotropic glutamate re ceptor subtype 1 (mGluR1) still was activated by extracellular Ca2+ ([Ca2+] (o)), but its function was severely compromised. Chimeric receptors with th e hCaR VFT and mGluR1 seven-transmembrane domain plus C-tail domain retaine d good response to [Ca2+](o) whether the Cys-rich domain was from hCaR or f rom mGluR1, Mutant hCaR with the Cys-rich domain deleted failed to respond to [Ca2+](o), although it was expressed at the cell surface and capable of dimerization. Our results indicate that the hCaR Cys-rich domain plays a cr itical role in signal transmission from VFT to seven-transmembrane domain. This domain tolerates a significant degree of amino acid substitution and m ay not be directly involved in the binding of [Ca2+](o).