PHYSARUM VITRONECTIN-LIKE PROTEIN HAS EXTENSIVE HOMOLOGY TO DIHYDROLIPOAMIDE ACETYLTRANSFERASE

Physarum vitronectin-like protein with a molecular mass of 70 kDa cros s-reacts with antibovine vitronectin and promotes cell-spreading (Miya zaki, K. et al. 1992. Exp. Cell Res., 199: 106-110.). The amino-termin al sequence of Physarum vitronectin-like protein is, however, distinct from those of animal vitronectins but shows significant sequence homo logy with dihydrolipoamide acetyltransferase, a component of pyruvate dehydrogenase complex. We have investigated the structural relationshi ps between Physarum vitronectin-like protein and dihydrolipoamide acet yltransferase by using both antibody and protein-chemical methods. The vitronectin-like protein reacted with both anti-bovine vitronectin Ig G and anti-rat pyruvate dehydrogenase complex IgG, indicating that it shares common antigenic determinant(s) with rat pyruvate dehydrogenase complex. Furthermore, sequencing studies of peptides obtained by lysy lendopeptidase digestion indicated that internal sequences of Physarum vitronectin-like protein show significant homology with dihydrolipoam ide acetyltransferase, but do not show any homology with the primary s tructures of authentic vitronectins. Immunocytochemistry revealed that the protein is widely localized in cytoplasm and nuclei of Physarum p olycephalum, but is not present in the central area of vacuoles. Our r esults indicate that Physarum vitronectin-like protein is a molecule s tructurally and immunologically related to dihydrolipoamide acetyltran sferase but functionally similar to animal vitronectin, although its l ocalization is unique.