Ionic strength-dependent isoforms of sea urchin egg dynein

Ciliary dynein of Paramecium tetraurelia: photolytic maps of the three heavy chains

The ciliate Paramecium tetraurelia presents a powerful system to define the structural basis for dynein functional diversity within a single cell. This analysis will depend on the biochemical resolution of the dynein proteins. As an important first step, the three heavy chains of the ciliary outer arm dynein of paramecium were characterized. Sucrose density gradient centrifugation in a high salt buffer separated the dynein into a 22S species, which contained the alpha and beta heavy chains, and a 12S species, which contained the gamma chain as well as the inner arm dynein heavy chains. Both the 22S and 12S species retained enzymatic latency as indicated by stimulation of MgATPase activity by 0.1% Triton X-100. An unusual ATP-independent V1-like photolysis of only the beta chain provided the basis for estimating that the beta chain contributes almost half of the 22S MgATPase activity that is susceptible to V1 photolysis. The combination of the density gradient separation of the partially dissociated dynein and the ATP-independent V1-like photolysis of only the beta chain led to the unambiguous assignment of the V1 photolytic products to the appropriate parent heavy chains. An estimate of the molecular sizes of the three heavy chains was obtained. The photolytic peptide maps, which define the ATP-binding domains, were determined for the three heavy chains.

Two distinct isoforms of sea urchin egg dynein

Extracts of unfertilized sea urchin eggs contain at least two isoforms of cytoplasmic dynein. One exhibits a weak affinity for microtubules and is primarily soluble. The other isoform, HMr-3, binds to microtubules in an ATP-sensitive manner, but is immunologically distinct from the soluble egg dynein (Porter et al.: Journal of Biological Chemistry 263:6759-6771, 1988). We have now further distinguished these egg dynein isoforms based on differences in NTPase activity. HMr-3 copurifies with NTPase activity, but it hydrolyzes CTP at 10 times the rate of ATP. The soluble egg dynein is similar to flagellar dynein in its nucleotide specificity; its MgCTPase activity is ca. 60% of its MgATPase activity. Non-ionic detergents and salt activate the MgATPase activities of both enzymes relative to their MgCTPase activities, but this effect is more pronounced for the soluble egg dynein than for HMr-3. Sucrose gradient-purified HMr-3 promotes an ATP-sensitive microtubule bundling, as seen with darkfield optics. We have also isolated a 20 S microtubule translocating activity by sucrose gradient fractionation of egg extracts, followed by microtubule affinity and ATP release. This 20 S fraction, which contains the HMr-3 isoform, induces a microtubule gliding activity that is distinct from kinesin. Our observations suggest that soluble dynein resembles axonemal dynein, but that HMr-2 is related to the dynein-like enzymes isolated from a variety of cell types and may represent the cytoplasmic dynein of sea urchin eggs.

Molecular cloning and expression of sea urchin embryonic ciliary dynein beta heavy chain

The determination of the structure and the expression of dynein during embryonic development are central to the understanding of dynein function. As an important first step toward these objectives, cDNAs encoding portions of sea urchin ciliary dynein were identified by antibody screening of a sea urchin cDNA expression library. Because of the complete lack of protein sequence data, it was first necessary to prove the identity of the dynein cDNAs. Of the five cDNA inserts initially cloned, one, designated P72A1, was characterized extensively. Four independent criteria demonstrated that P72A1 encoded a portion of a dynein heavy chain. (1) The beta-galactosidase-P72A1 fusion protein affinity-purified dynein-specific antibodies from crude antiserum. (2) Two other antisera to dynein, raised independently of the antiserum used to screen the cDNA library, reacted with the fusion protein. (3) A new antiserum raised against the fusion protein reacted with authentic dynein heavy chain on Western blots and stained embryonic cilia by indirect immunofluorescence microscopy. (4) Two new antisera, elicited against opposite ends of the P72A1 open reading frame, each reacted with authentic dynein heavy chain protein. Western blot analyses of dissociated dynein heavy chains revealed that P72A1 encoded a portion of the beta heavy chain. Epitope mapping experiments confirmed the identity of P72A1 as part of the beta heavy chain and also demonstrated that P72A1 encoded epitopes of the carboxyl-terminal fragment B domain of the dynein beta heavy chain. Northern blot analyses of poly(A)+ RNA revealed that P72A1 hybridized with a large RNA species ca. 12.5 kb in length. The dynein mRNA concentration increased during embryonic development. Dot blot analyses of RNA isolated at various times after embryo deciliation demonstrated that the dynein beta heavy chain mRNA accumulated rapidly in response to deciliation. The accumulation was similar to but not identical with the induction of tubulin mRNA in response to the same stimulus.

Preparation of microtubules from rat liver and testis: cytoplasmic dynein is a major microtubule associated protein

A microtubule associated protein from brain tissue (MAP 1C), has been found to possess many properties in common with ciliary and flagellar dyneins (Paschal et al.:J. Cell Biol. 105:1273-1282, 1987). However, this protein, now designated as cytoplasmic dynein, exhibited several properties which distinguish it from axonemal forms of the enzyme. We have investigated these characteristics further in a study of cytoplasmic dyneins from non-neuronal tissues. Rat liver and testis in particular were found to contain high levels of cytoplasmic dynein. The yield of dynein from testis was over 70 micrograms/g of tissue, making this the best source of cytoplasmic dynein of all tissues so far examined. The characterization of dynein from these sources has confirmed and extended our previous observations concerning the unique properties of cytoplasmic dynein. Activation of liver and testis dynein occurred at low (less than 1 mg/ml) tubulin concentration. Polypeptides identified as subunits of brain cytoplasmic dynein (74, 59, 57, 55, and 53 kDa) were present in liver and testis preparations. In addition, polypeptides at 150 and 45 kDa were found to copurify with the non-neuronal dyneins. The liver and testis enzyme hydrolyzed pyrimidine nucleotides at rates up to 12.5 times faster than ATP, though the relative affinity of cytoplasmic dynein for CTP was much lower (Km = 1.0 mM) than that for ATP. The properties of the testis enzyme were consistent with its identification as a cytoplasmic dynein rather than a sperm axonemal precursor. These data indicate that cytoplasmic dyneins may be widespread in distribution and that they share certain biochemical properties unique from those of axonemal dyneins. These characteristics are consistent with the proposal that cytoplasmic dynein plays a universal role in retrograde organelle motility.