Proline hydroxylation alters the electrophoretic mobility of pulmonary surfactant‐associated protein A

Studies from several laboratories involving amino acid analysis and sequencing of the M_r 35 000 pulmonary surfactant‐associated proteins (SP‐A) have detected hydroxyproline residues. These residues are present in a region with a collagen‐like sequence that has been revealed by direct amino acid sequencing and from the deduced amino acid sequence of the cDNA clones coding for SP‐A. We treated human lung tissue with tunicamycin to block N‐glycosylation and with 2,2‐dipyridyl to inhibit the hydroxylation of proline residues. The SP‐A synthesized under these conditions showed a shift in apparent molecular weight to 27 000 and 29 000 compared to 29 000 and 31 000 for SP‐A synthesized in the presence of tunicamycin alone. Dipyridyl treatment alone caused an alteration in electrophoretic mobility similar to that seen with tunicamycin, although this was more difficult to evaluate since changes in molecular weight due to glycosylation occurred under these conditions. These results indicate that proline hydroxylation in the collagen‐like portion of SP‐A decreases its electrophoretic mobility.