INNER AND OUTER ARM AXONEMAL DYNEINS FROM THE ANTARCTIC ROCKCOD NOTOTHENIA-CORIICEPS

Adaptive compensation of enzymatic activities is common among cold-liv ing poikilotherms. Their enzymes often demonstrate higher activities a t low temperatures than do homologs from temperate or thermophilic spe cies. To understand the molecular features necessary for cold adaptati on of microtubule motor proteins, we have initiated studies of the fla gellar dynein ATPases of Antarctic fishes (body temperature range = -1 .8 to +2 degrees C). Dyneins were isolated by high-salt extraction of demembranated sperm axonemes from the Antarctic yellowbelly rockcod, N otothenia coriiceps. Although solubilization of inner arms was incompl ete, an inner arm dynein was recognized as a discrete complex containi ng one major dynein heavy chain (DHC) and sedimenting through sucrose gradients at similar to 12 S. Like inner arm dyneins from Chlamydomona s, the fish complex contained an actin-immunoreactive protein of 43 kD a and a 30-kDa protein. One isoform of the inner arm DHC gene family o f N. coriiceps was detected by the polymerase chain reaction, and Sout hern analysis established that this DHC gene is present at one copy pe r haploid genome. Outer arm dynein was extracted quantitatively by hig h-salt treatment, contained two DHCs (one major, one minor), and sedim ented through sucrose gradients as a polydisperse, aggregating system. Associated with the outer arm DHCs were five presumptive intermediate chains (ICs) of 66-91 kDa, immunologically defined by their cross-rea ctivity to four monoclonal antibodies specific for ICs from other orga nisms. The basal (non-microtubule-stimulated) specific ATPase activiti es of the N. coriiceps inner and outer arm dyneins were similar to 0.0 7 and similar to 0.04 mu mol of P-i min(-1) mg(-1), respectively, at 0 degrees C, attained their maxima (similar to 0.1 mu mol of P-i min(-1 ) mg(-1)) at 9 and 19 degrees C, respectively, and at higher temperatu res declined substantially. Furthermore, the activities of the fish dy neins at temperatures less than or equal to 15 degrees C were signific antly larger than that of outer arm dynein from the mesophile Tetrahym ena. These results suggest that the greater catalytic efficiencies of N. coriiceps inner and outer arm dyneins at low temperatures are due t o enhanced polypeptide flexibility in the active sites of their protei n subunits. We conclude that temperature adaptation of flagellar dynei ns from Antarctic fishes is compatible with substantial conservation o f primary and quaternary structure.