The structure and stability of human plasma cold-insoluble globulin.

TLDR

The molecular properties of cold‑insoluble globulin were examined by velocity centrifugation, circular dichroism, and fluorescence at neutral and alkaline pH. The study proposes that cold‑insoluble globulin consists of multiple domains linked by flexible polypeptide segments. The authors evaluated thermal and guanidine hydrochloride stability and measured frictional ratio changes between pH 7.0 and 11.0, attributing the increase to expansion of flexible segments while domains remained largely unchanged. The protein’s properties closely parallel those of fibronectin, confirming structural identity, and its domains remain stable up to ~55 °C at pH 7.0 but only ~40 °C at pH 11.0.

Abstract

The molecular properties of cold-insoluble globulin have been investigated by velocity centrifugation, circular dichroism, and fluorescence at neutral and alkaline pH. The stability of the protein to thermal and guanidine hydrochloride has been evaluated under both conditions. The close parallelism between the properties of cold-insoluble globulin and those of the cell surface protein (fibronectin) serve to establish the essential identity of the structures of the two proteins derived from different sources. It is suggested that the cold-insoluble globulin is composed of several domains connected by flexible polypeptide segments. The large increase in the frictional ratio observed between pH 7.0 and 11.0 can be explained by an expansion of the flexible segments without significant change in the domains. These domains are stable to about 55 degrees C at pH 7.0 but only to about 40 degrees C at pH 11.0.