 RCA proteins typically possess CCP domains, also termed Sushi domains or Short Consensus Repeats (SCR).Such beta-sandwich domains contain about 60 amino acid residues, each with 4 conserved cysteines arranged in two conserved disulfide bonds (oxidized in 'abab' manner), and a conserved tryptophan, but otherwise can vary greatly in sequence.Recently, it has been demonstrated that the order, spatial relationship, and structure of these domains is essential for determining function.