Clusterin, a Binding Protein with a Molten Globule-like Region

Abstract

Clusterin is a heterodimeric glycoprotein found in many tissues of the body and is the most abundant protein secreted by cultured rat Sertoli cells. The function of clusterin is unknown, but it has been associated with cellular injury, lipid transport, apoptosis, and it may be involved in the clearance of cellular debris caused by cell injury or death. Consistent with this last idea, clusterin has been shown to bind to a variety of molecules with high affinity including lipids, peptides, and proteins and the hydrophobic probe 1-anilino-8-naphthalenesulfonate (ANS). Given this variety of ligands, clusterin must have specific structural features that provide the protein with its promiscuous binding activity. Using sequence analyses, we show that clusterin likely contains three long regions of natively disordered or molten globule-like structures containing putative amphipathic alpha-helices. These disordered regions were highly sensitive to trypsin digestion, indicating a flexible nature. The effects of denaturation on the fluorescence of the clusterin-ANS complex were compared between proteins with structured binding pockets and molten globular forms of proteins. Clusterin bound ANS in a manner that was very similar to that of molten globular proteins. Furthermore, we found that, when bound to ANS, at least one cleavage site within the protease-sensitive disordered regions of clusterin was protected from trypsin digestion. In addition, we show that clusterin can function as a biological detergent that can solubilize bacteriorhodopsin. We propose that natively disordered regions with amphipathic helices form a dynamic, molten globule-like binding site and provide clusterin the ability to bind to a variety of molecules.

Clusterin and COMMD1 Independently Regulate Degradation of the Mammalian Copper ATPases ATP7A and ATP7B

“…Clusterin possesses molten globular-like structures that contain putative amphipathic ␣-helices (38). This structure allows clusterin to interact with the hydrophobic regions of many proteins exposed following stress (24).…”

Intrinsic disorder in spondins and some of their interacting partners

“…It is known that the presence of intrinsic disorder can serve as one of the bottlenecks in structural characterization of a target protein that can affect several processes of the structure determination pipeline, such as expression and stability, 187,188 as well as solubility, 189,190 and predisposition for crystallization. 189,[191][192][193][194][195][196] In application to spondins and their partners, this hypothesis is supported by the observation that proteins with more predicted disorder typically have lower structure coverage. Data presented in our study revealed that spondins and their binding partners contain considerable levels of disorder and intrinsic disorder might be related to functionality of these proteins.…”

From Humans to Experimental Models: The Cytoprotective Role of Clusterin in the Kidney

“…The primary structure of sCLU in both α-and β-chain subunits contains several large molten globule domains, amphipathic regions and coiled-coil α-helices [9,[33][34][35], which are typical of molecular chaperone -conformational adaptability to allow CLU protein to bind its substrate proteins or lipids with high affinity and low specificity [35][36][37]. Furthermore, one study has revealed that the glycosylation of sCLU may not be required for its overall secondary structure content and binding activity to its substrate [38].…”