Abstract：In this study, we first molecularly cloned sheep C3d from RNA of the sheep liver, and compared with the C3d gene of other animals available in GenBank at nucleotide and amino acid leves. The 909bp cDNA of sheep C3d f encodes a polypeptide of 303 amino acids consisting of 1 potential Glycosaminoglycan attachment sites（SG.G）, 2 Protein kinase C phosphorylation sites([ST].[RK]) , 1Tyrosine kinase phosphorylation site, 2 N-myristoylation sites and 1 Casein kinase II phosphorylation site. The amino acid sequence similarity of C3d between human, bovine, goat, boar, golden hamste,rmouse,brown rat,Macropus, hare,Gallus is 80.4% ,94.7% ,96.9% ,82.8% ,81.1% ,80.6% ,80.2%,71.0% ,75.2% and60.3% respectively..Helix and angles turns out alternately in Sheep C3d second structure, which helix accounted for 55.12%, strand to 2.31%and coil for the 42.57% of such a structure conducive to the performance of barrel-shaped structure is formed. ESyPred3D through homology modeling forecast sheep C3d three known structures C3d with the same people also formed by nuclear heart and the outer form of the performance of barrel-shaped molecular structure. The experiment not only for livestock C3d in the immunological basis to provide experimental evidence, but also for the construction of high immunogenicity of vaccine gene lay the foundation for the new technology.
