Sasirekha Narayanasamy

In eukaryotic cells, Ca2+ signals play a crucial role in the regulation of many cellular processes, e.g., gene expression, cytoskeleton dynamics, cell cycle, cell death, neurotransmission, and signal transduction. To achieve its role as messenger, the intracellular Ca2+ concentration ([Ca2+]) is very tightly regulated in time, space, and magnitude. The biological role of calcium is mainly fulØlled by its binding with different classes of Ca2+ binding proteins (CaBPs). Calcium, in addition to stabilizing these proteins, it also induces conformational changes. Most Ca2+-binding proteins act as functional switches controlling a physiological phenomenon (Yang et al., 2006). The mode and mechanism of interaction of Ca2+ with CaBPs helps in understanding the proteins’ ability to transduce signal transduction within a cell (Chary et al., 2007). Histidine rich calcium binding protein (HRC) is a high capacity, low affinity Ca2+-binding protein, residing in the lumen of the Sarcoplasmic reticulum (SR). HRC has been associated into the SR protein complex and implicated in various pathological conditions. However, the regions that are involved in Ca2+-binding and the mode at which it binds Ca2+ and the high-resolution structure are currently unknown. Also, the biophysical attributes as a calcium-binding protein and the structural implications upon binding to Ca2+ are largely unknown. On account of these observations, molecular characterization of HRC assumes extreme importance.