The C1QA protein helps form C1, the starting component of the serum complement system. C1q binds to the zymogens C1r and C1s, resulting in C1 assembly. C1QA Protein, Mouse (His-SUMO) is the recombinant mouse-derived C1QA protein, expressed by E. coli , with N-6*His, N-SUMO labeled tag.