Prokaryotic homolog of tubulin? Consideration of FtsZ and glyceraldehyde 3-phosphate dehydrogenase as probable candidates.

The bacterial FtsZ protein has recently been suggested as a probable prokaryotic homolog of the tubulin family of proteins (Cell 80, 1995, 367-370). We have compared the sequence similarity of tubulins to FtsZ and another protein glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Both these proteins exhibited similar levels of sequence identity to the tubulins, which in a few cases was indicated to be significant. We report that incubation of the GAPDH in microtubule assembly buffer causes its polymerization into filamentous structures. In eukaryotic cells, GAPDH is known to be associated with cytoskeletal structures and it binds specifically to both tubulins and colchicine. The latter is a distinctive characteristic of the tubulin family of proteins. These observations indicate that similar to the FtsZ proteins, GAPDH also exhibits a number of intriguing similarities to the tubulins. Whether any of these proteins truly represent the prokaryotic homolog of tubulin, however, is unclear at present.