A FORMIMINOTRANSFERASE CYCLODEAMINASE ISOFORM IS LOCALIZED TO THE GOLGI-COMPLEX AND CAN MEDIATE INTERACTION OF TRANS-GOLGI NETWORK-DERIVED VESICLES WITH MICROTUBULES

A protein of 60 kDa (p60) has been identified using a quantitative in vitro vesicle-microtubule binding assay. Purified p60 induces co-sedim entation with microtubules of trans-Golgi network-derived vesicles iso lated from polarized, perforated Madin-Darby canine kidney cells. Sequ encing of the cDNA coding for this protein revealed that it is the chi cken homologue of formiminotransferase cyclodeaminase (FTCD), a liver specific enzyme involved in the histidine degradation pathway. Purifie d p60 from chicken liver has formiminotransferase activity, confirming that it is FTCD or an isoform of this enzyme. Isoforms of FTCD were i dentified in chicken hepatoma and HeLa cells, and immunolocalize to th e region of the Golgi complex and vesicular structures in its vicinity . Furthermore, 58K, a previously identified microtubule-binding Gels p rotein from rat liver (Bloom, G. S., and Brashear, T. A. (1989) J. Bio l. Chem. 264, 16083-16092), is identical to FTCD. Both proteins co-pur ify with microtubules and co-localize with membranes of the Gels compl ex. The capacity of FTCD to bind both to microtubules and Golgi-derive d membranes may suggest that this protein, or one of its isoforms, mig ht have in addition to its enzymatic activity, a second physiological function in mediating interaction of Gels-derived membranes with micro tubules.