Conformational Variations of Human C1q in Different Buffers

Abstract

C1q is a primary activator of Complement system and has a physiological role in maintaining the homeostasis. C1q is now acknowledged as a protein of complex functionality, capable of forming multiple binding sites for ligands of various nature by its C-terminal globular domains (gC1q), composed of the globular fragments of the three types of chains, ghA, ghB and ghC. The conformation of the globular fragments is critical for the formation of different binding sites underlying the functional activity of C1q. We studied the conformational flexibility of C1q and its globular fragments ghA, ghB and ghC in different routinely used buffers by the highly sensitive fluorescent spectroscopy. We compared the conformational state of C1q in PBS, pH 7.2; TBS, pH 7.2; carbonate buffer, pH 9.6; NaHCO3, pH 7.2 and HEPES, pH 7.2. HEPES buffer appeared most favourable solute in terms of conformational stability of C1q. The ghB of all three globular fragments followed most closely the native protein.