This is a histidine-rich calcium binding repeat which appears in proteins called histidine-rich-calcium binding proteins (HRC). HRC is a high capacity, low affinity Ca2+-binding protein, residing in the lumen of the sarcoplasmic reticulum. HRC binds directly to triadin. This binding interaction occurs between the histidine-rich region of HRC and multiple clusters of charged amino acids, named as the KEKE motifs, in the lumenal domain of triadin. The region in which this repeat is found in many copies is long and variable but is the acidic region of the protein. There is also a cysteine-rich region further towards the C-terminus. HRC may regulate sarcoplasmic reticular calcium transport and play a critical role in maintaining calcium homeostasis and function in the heart. HRC as a candidate regulator of sarcoplasmic reticular calcium uptake.