Mediates adhesion of proximal tubule epithelial cells via integrins alpha3-beta1 and alphaV-beta3. This is a non catalytic peptidase C1 family protein. Expressed in the kidney cortex, small intestine and cornea. Initially observed in the Bowman capsule during early glomerular capillary loop formation in the kidney. In more developmentally mature glomeruli, following transition from early to mid-capillary loop stage, expression is higher in the proximal tubular basement membrane than in the distal basement membrane and Bowman capsule. It has been suggested that the active SMB domain may be permitted considerable disulfide bond heterogeneity or variability, thus 2 alternate disulfide patterns based on 3D structures are described with 1 disulfide bond conserved in both. Antibodies against TINAG are found in sera of patients with tubulointerstitial nephritis, a rare autoimmune disorder that causes acute and chronic renal injury. Major isoform. Belongs to the peptidase C1 family.