Calcium is one of the most important ions in the human body. As divalent ion it is used for many different cellular mechanisms such as B- and T-cell activation, mast cell degranulation, gene expression and muscle contraction. Calcium used for cell-signaling pathways is mainly stored in the endoplasmic reticulum (ER). When the stores are depleted they have to be refilled. The best-known pathway to achieve Ca2+ store-refilling, is the store-operated calcium entry (SOCE). For SOCE two proteins STIM1 and Orai1 are essential. STIM1 is the Ca2+-sensor in the ER being activated after store depletion, wherease the Orai1 channel resides in the plasma membrane. The best characterized SOCE is the so called Ca2+ release activated Ca2+ (CRAC) channel. Up to now, only the crystal structure of Orai1 in Drosophila melanogaster (dOrai1) is resolved. This dOrai1 is a hexamer with four transmembrane (TM) regions each. Six of the transmembrane 1 (TM1) region form the pore of the channel. A recently released paper of Alavizargar et al. showed MD-simulations of the E190Q mutation in dOrai1. This simlation showed a widening of the pore in the presence of the E190Q mutant. In my thesis I wanted to investigate, if there is a widening as well in human Orai1 (hOrai1). To investigate this theory in a biological context, cross-linking experiments were carried out to see possible structural changes within the pore.