First Structural Glimpse of CCN3 and CCN5 Multifunctional Signaling Regulators Elucidated by Small Angle X-ray Scattering

Abstract

The CCN (cyr61, ctgf, nov) proteins (CCN1-6) are an important family of matricellular regulatory factors involved in internal and external cell signaling. They are central to essential biological processes such as adhesion, proliferation, angiogenesis, tumorigenesis, wound healing, and modulation of the extracellular matrix. They possess a highly conserved modular structure with four distinct modules that interact with a wide range of regulatory proteins and ligands. However, at the structural level, little is known although their biological function(s) seems to require cooperation between individual modules. Here we present for the first time structural determinants of two of the CCN family members, CCN3 and CCN5 (expressed in Escherichia coli), using small angle x-ray scattering. The results provide a description of the overall molecular shape and possible general three-dimensional modular arrangement for CCN proteins. These data unequivocally provide insight of the nature of CCN protein(s) in solution and thus important insight into their structure-function relationships.

CCN2/CTGF regulates neovessel formation via targeting structurally conserved cystine knot motifs in multiple angiogenic regulators

“…This novel action of CCN2/CTGF may lead to several modulatory effects such as protection binding proteins from proteolytic destruction, sequestering factors in ECM at the sites of an injury, and stabilizing or destabilizing angiogenic ligand/receptor interactions. Our finding is consistent with the first structural determinants of CCNs using small‐angle X‐ray scattering, in which CCN proteins exist in the ECM as long extended scaffolds able to move and flex to allow multiple modules to bind a ligand (39). The CCN2/CTGF I–III mutant with a broad binding activity and a potent antiangiogenic activity shows therapeutic potential that may affect multiple key angiogenic pathways.…”

The CCN family acting throughout the body: recent research developments

“…At present, little is known about the tertiary structure of the CCN family proteins. One previous report indicated that CCN3 and CCN5 are rich in β-strands and random coils, as evaluated by circular dichroism spectrum analysis and that both form extended, rather than globular, shapes in solution as determined by X-ray scattering analysis and in silico modeling (11). Further structural characterization may clarify the functional role of such novel structural features of CCN family proteins in the future.…”

Adhesion-modulating/matricellular ECM protein families: A structural, functional and evolutionary appraisal

“…The presence of many cysteine residues in CCN proteins has impeded efforts at protein analysis. Recent small angle X-ray scattering analysis of purified CCN3 and CCN5 in solution indicated an extended conformation with considerable flexibility: it is suggested that this would allow for regulation of protease sensitivity of the hinge region or accessibility of the receptor binding sites on different domains (Holbourn et al, 2011).…”