Immunochemical and biochemical evidence for distinct basement membrane heparan sulfate proteoglycans.

Two antigenically and structurally related heparan sulfate proteoglycans (HSPG), with masses of 200 and 350 kDa, have been isolated and characterized from bovine renal tubular basement membranes (BTBM) using DEAE-Sephacel, octyl-Sepharose CL-4B, and Propac PA-1 chromatography. Heparitinase treatment revealed core proteins of 145 and 125 kDa, with corresponding core proteins after trifluoromethanesulfonic acid treatment of 88 and 82 kDa, from the 200- and 350-kDa HSPGs, respectively. The separated HSPGs produced similar tryptic peptide maps, had similar amino acid compositions, and had similarly sized GAG chains. The 200-kDa HSPG had 2.1 mg of protein/mumol of hexuronic acid compared with 1.1 mg/mumol for the 350-kDa HSPG. Anti-BTBM HSPG monoclonal antibody (mAb A12) reacted with core proteins derived from the 200- and 350-kDa HSPGs, whereas anti-perlecan polyclonal and monoclonal antibodies did not bind to the BTBM HSPG core proteins described above but reacted with a 230-kDa core protein, which was nonreactive with mAb A12. Immunohistochemical studies of the kidney demonstrated differences in the distribution of BTBM HSPG and perlecan. Comparison of amino acid sequences from BTBM HSPG tryptic peptides with the sequence of perlecan revealed similarities but not extensive identity. Two tryptic peptides show homology to rat agrin, a basement membrane component of synaptic junctions. These data suggest that the two BTBM HSPGs are immunologically and structurally related and that differences in these molecules may arise from alternative splicing or posttranslational modifications. In addition, the two BTBM HSPGs are immunologically and structurally distinct from perlecan but may share homology with agrin.