Chemical analysis and electron microscopy studies of human C1q prepared by different methods

Abstract

Five differently isolated and purified human C1q preparations were examined by electron microscopy and analyzed by polyacrylamide gel electrophoresis in 0.1% sodium dodecyl sulfate and 0.5 M urea. The amino acid and carbohydrate composition of C1q purified by the DNA method are reported and compared with results obtained on C1q isolated by other procedures. Electron microscopy showed that all C1q preparations had six peripheral subunits connected by fibrillar strands to a central subunit. The presence of small amounts of dimers was also observed. The physico-chemical properties of the molecule are independent of the purification method used. The five C1q preparations labeled with 125I in presence of lactoperoxidase formed two types of noncovalently linked subunits. In each case the smaller (central) subunit contained over thirty times as much radioactivity as the larger (peripheral) subunit supposed to interact with immune complexes. Reduction and alkylation confirmed for each preparation the presence of three polypeptide chains, the smaller of which contained essentially all radioactivity.

The Disulfide Bonding Pattern in Ficolin Multimers

“…Ficolins and collectins consist of a short N-terminal domain, which may be used for multimerization, a middle collagen domain, and a C-terminal globular domain that binds carbohydrate (19 -26). This structure is also similar to complement protein C1q (21). The primary difference between ficolins and collectins is that the C-terminal globular domain of ficolin is a fibrinogen-like (fbg) domain, whereas that of collectins is a carbohydrate recognition domain (12)(13)(14)26).…”

The Classical and Regulatory Functions of C1q in Immunity and Autoimmunity

“…A C1q consists of 6 such triple helical structures which are held together through inter-chain disulphide bonds at the N-terminal ends (Figure 1). It is viewed as a "bundle-of-tulips" under the electron microscope (66). Earlier work has established conditions for the selective degradation of the collagenous or globular regions of C1q to evaluate the functions of each region in the absence of the other (67,68).…”

Purification and characterization of subcomponent C1q of the first component of bovine complement

“…The collagen helices come together at the other end to generate a fibril-like assembly. This results in an appearance in the electron microscope of a 'bowl of tulips' (Knobel et al, 1975), the six subunits having globular heads, the flowers, with collagen triple helices, the stems, coming together to form the fibril or pot-like structure at the base.…”