FKBP36 forms complexes with clathrin and Hsp72 in spermatocytes.

The testes-specific peptidyl-prolyl cis/ trans isomerase FKBP36 plays a crucial role in male meiosis. Here we show that the catalytic domain of FKBP36 binds to clathrin heavy chain (CHC) of clathrin. Despite wild-type FKBP36 not displaying PPIase activity, the introduction of the R81L substitution resulted in catalysis of prolyl isomerization, which is comparable to the regulated activity of FKBP38. Furthermore, the TPR domain of FKBP36 interacts with Hsp72. In fact, FKBP36 preferentially binds to Hsp72 among the members of the Hsp70 family and is thus the first TPR-containing protein which discriminates between Hsp70 proteins. The clathrin-FKBP36-Hsp72 complexes resulting from both identified interactions are bound to the matrices of clathrin-coated vesicles in spermatocytes, which indicates a possible role of FKBP36 and Hsp72 in the disassembly of clathrin coats.