Construction And Functional Study Of Human Cubilin Protein Mutants

Excessive resorption of albumin by renal tubular epithelial cells may cause renal injury through multiple mechanisms and ultimately result in chronic renal failure. Cubilin is a pinocytotic receptor distributing on the brush border of proximal tubular epithelial cells and responsible for reabsorb large-molecule substances such as albumin. Cubilin-defective humans and dogs present with serious albuminuria, but not with apparent pathological changes of the kidney; moreover, they will not develop chronic renal failure. We demonstrated that in patients with nephritic syndrome, cubilin expression is upregulated in renal tubular epithelial cells and resorption of albumin is increased, which is associated with upregulated expression of renal tubular interstitial MCP-1 and RANTES and infiltration of inflammatory cells; whereas, antisense cubilin RNA can suppress excessive resorption of albumin and significantly downregulate the expression of MCP-1 and RANTES by renal tubular epithelial cells, suggesting that cublilin plays an important role in mediating albumin overload-induced renal tubular interstitial lesion.Full-length Cubilin is composed of 3623aa (molecular weight, 460kD), involving 8 EGF-like domains at N-terminal and 27 CUB domains. The CUB domains are also the main functional domains, responsible for binding to most of ligands. Of them, CUB7-8 domains bind to albumin; nevertheless, the essential amino acid residues for binding have not been determined yet. Protein-protein interaction or recognition is based on specific spatial structures formed by peptide segments within protein molecules (for instance, the"ligand-binding pocket"is responsible recognition and binding of receptor and ligand); therefore, several essential functional residues are frequently enough for determining the efficiency of interaction. According to different biological properties of segments of Cubilin, functional fragments CUB7-8 were investigated. The spatial structure of CUB8 functional domain was built by homologous modeling, and candidate functional residues of CUB8 functional domain that bind to albumin were predicted by computer-aided molecular...