Transglutaminase from rat coagulating gland secretion - Post-translational modifications and activation by phosphatidic acids

Structural and biochemical characteristics of transglutaminase purified by a rapid chromatographic procedure from the rat coagulating gland (anterior prostate) secretion are reported. Fast atom bombardment mapping and automated Edman degradation experiments allowed us to verify that at least 85% of the entire transglutaminase amino acid sequence is identical to that derived from the cDNA of the major androgen-dependent rat prostate protein called DP1, The enzyme was found NH2 terminally blocked and largely posttranslationally modified, since the presence of N-linked oligosaccharides, as well as of complex lipidic structures, was observed, Mass spectral analysis showed that Asn-408 and -488 are the glycosylated sites, the N-linked structures identified belonging to both high-mannose and complex type glycans. The presence of myo-inositol, of glycerol bound fatty acids, and the high content of mannose residues, are in agreement with previous observations suggesting, that a Lipid anchor is bound to coagulating gland secretion transglutaminase, Furthermore, two tightly bound calcium ions per molecule of enzyme were detected, Finally, a strong stimulation of the enzyme activity in vitro by both SDS and a variety of phosphatidic acids was observed. The reported structural and functional peculiarities should definitively lead to consider She prostate enzyme as a new member (type IV) of the transglutaminase family.