INTERACTION OF TROPONIN-H AND GLUTATHIONE S-TRANSFERASE-2 IN THE INDIRECT FLIGHT MUSCLES OF DROSOPHILA-MELANOGASTER

Drosophila indirect flight muscles (IFMs) contain a 35 kDa protein whi ch cross-reacts with antibodies to the IFM specific protein troponin-H isoform 34 (TnH-34). Peptide fingerprinting and peptide sequencing sh owed that this 35 kDa protein is glutathione S-transferase-2 (GST-2). GST-2 is present in the asynchronous indirect flight muscles but not i n the synchronous tergal depressor of the trochanter (jump muscle). Ge netic dissection of the sarcomere showed that GST-2 is stably associat ed with the thin filaments but the presence of myosin is required to a chieve the correct stoichiometry, suggesting that there is also an int eraction with the thick filament. The two Drosophila TnHs (isoforms 33 and 34) are naturally occurring fusion proteins in which a proline-ri ch extension of similar to 250 amino acids replaces the 27 C-terminal residues of the muscle-specific tropomyosin II isoform. The proteolyti c enzyme, Igase, cleaves the hydrophobic C-terminal sequence of TnH-34 at three sites and TnH-33 at one site. This results in the release of GST-2 from the myofibril. The amount of GST-2 stably bound to the myo fibril is directly proportional to the total amount of undigested TnH. It is concluded that GST-2 in the thin filament is stabilized there b y interaction with TnH. We speculate that the hydrophobic N-terminal r egion of GST-2 interacts with the hydrophobic C-terminal extension of TnH, and that both are close to a myosin cross-bridge. (C) Chapman & H all Ltd.