The human complement receptor type I (CRI, C3b/C4b receptor) has attracted keen interests as an inhibitor for inflammatory and immune system. Recently CR1 was demonstrated to suppress the hyper-acute rejection in xeno-transplantation and to cure autoimmune diseases. sCR1, a soluble form of CR1, is a recombinant protein of CR1 in which the transmembrane domain at C-terminus was cleaved off and could be over-expressed in Chinese hamster ovary (CHO) cells. Previously, we reported a novel and simple method to produce and purify sCR1 [Kato et al. Biotechnol. Bioprocess. Eng. 7 (2002) 67]. In this study, we purified the derivative of sCR1, called as aglyco-sCR1, by treating sCR1 with tunicamycin so as to remove glyco-chains or to inhibit the glycosylation on CR1 protein during cell cultivation. Both sCR1 and aglyco-sCR1 proteins were examined by transmission electron microscopy. The sCR1 molecules were monodispersed in an appropriate surfactant which showed a square shape with a side length of 11.6 nm, whereas aglyco-sCR1 showed disc-like shape with a diameter of 8.2 nm having a concave at its center and formed larger oligomeric disc-like shaped assemblies with a diameter of 19.0 nm. The lack of the glyco-chains may facilitate aglyco-sCR1 to form oligomeric disc-like architectures so as to stabilize the structure in the solution. These facts may suggest that glyco-chains play an important role in the functions of glyco-protein, and the lower activity of aglyco-sCR1 in comparison with that of sCR1 to suppress the complement activation may due to the assembly formation and the dynamic changes occurred in protein morphology. (C) 2003 Elsevier Inc. All rights reserved.