Hideto Fukushima

Titin-isoform dependence of titin-actin interaction and its regulation by S100A1/Ca2+ in skinned myocardium.

Titin, also known as connectin, is a large filamentous protein that greatly contributes to passive myocardial stiffness. In vitro evidence suggests that one of titins spring elements, the PEVK, interacts with actin and that this adds a viscous component to passive stiffness. Differential splicing of titin gives rise to the stiff N2B and more compliant N2BA isoforms. Here we studied the titin-isoform dependence of titin-actin interaction and studied the bovine left atrium (BLA) that expresses mainly N2BA titin, and the bovine left ventricle (BLV) that expresses a mixture of both N2B and N2BA isforms. For comparison we also studied mouse left ventricular (MLV) myocardium which expresses predominately N2B titin. Using the actin-severing protein gelsolin, we obtained evidence that titin-actin interaction contributes significantly to passive myocardial stiffness in all tissue types, but most in MLV, least in BLA, and an intermediate level in BLV. We also studied whether titin-actin interaction is regulated by S100A1/calcium and found that calcium alone or S100A1 alone did not alter passive stiffness, but that combined they significantly lowered stiffness. We propose that titin-actin interaction is a “viscous break” that is on during diastole and off during systole.

Myosin heavy chain genes expressed in juvenile and adult silver carp Hypopthalmichthys molitrix: novel fast-type myosin heavy chain genes of silver carp.

Silver carp Hypopthalmichthys molitrix is eurythermal temperate fish, whose muscle is considered to express several types of myosin heavy chain (MYH) genes at different stages of its growth and to adjust to the environmental temperature. In this study, MYH genes expressed in the muscles of juvenile and adult silver carp were investigated. Five types of MYH cDNA clone were isolated from silver carp (H. molitrix) by RACE strategy using a set of fast-type MYH specific primers, and termed scMYH(F1), scMYH(F2), scMYH(F3), scMYH(F4) and scMYH(F5) in the order of their abundance in cDNA libraries constructed from fast skeletal muscles of adult silver carp. scMYH(F1), scMYH(F3) and scMYH(F5) showed high nucleotide sequence identities of 96, 98 and 96% to gcMYH(F30), gcMYH(F10) and gcMYH(FI), respectively, that encode MYHs predominantly expressed in fast skeletal muscle of grass carp (Ctenopharyngodon idella) acclimated to 30, 10 and 20 degrees C, respectively. scMYH(F2) and scMYH(F4) showed a high identity to A4-type MYH from rock cod (Notothenia coriiceps) slow skeletal muscle. Phylogenetic analysis demonstrated that scMYH(F1) and scMYH(F5) were monophyletic with fish adult fast-type MYHs, whereas scMYH(F2) and scMYH(F4) formed a cluster with fish slow-like fast-type MYH, and scMYH(F3) did with fish embryonic fast-type MYHs. Interestingly, juvenile silver carp predominantly expressed scMYH(F3) irrespective of acclimation temperatures at 10, 18 or 26 degrees C. The comparison among scMYH(F1), scMYH(F2) and scMYH(F3) in the deduced amino acid sequence revealed that the putative binding sites for ATP, actin, and essential and regulatory light chains in myosin subfragment-1 (S1) have high identities with each other (81-100%). However, their loop-1 and loop-2 regions in S1 were highly variable, suggesting their different functions. The deduced amino acid sequences of myosin subfragment-2 and L-meromyosin showed high identities of 90-91% and 86-90%, respectively, among the above three scMYHs.

Changes in enzymatic and structural properties of grass carp fast skeletal myosin induced by the laboratory-conditioned thermal acclimation and seasonal acclimatization

Myosins were prepared from fast skeletal muscles of grass carp thermally acclimated to 10, 20 and 30°C in the laboratory as well as from those seasonally acclimatized and collected in January (winter) 2003 and May (spring), August (summer) and November (autumn) 2002. The maximal initial velocities (Vmax) of actin-activated Mg2+-ATPase activity for myosins from the 10°C-acclimated and winter grass carp were 1.7–1.8-fold as high as those from the 30°C-acclimated and summer fish. The inactivation rate constant (KD) of Ca2+-ATPase for myosin from the 10°C-acclimated grass carp was three to fourfold higher than those for myosins from the fish acclimated to 20°C and 30°C, whereas myosin from winter grass carp was about sevenfold as high as that for myosin from summer fish. Myosins from spring and autumn fish showed KD values comparable to those of the fish acclimated to 30°C and 10°C, respectively. In differential scanning calorimetry analysis, the transition temperature (Tm) was observed near 38°C and 45–46°C with most myosins. However, the lowest Tm at 32–33°C was given as one of the major endotherms in myosins from the 10°C-acclimated, autumn and winter fish. These responses of grass carp to changed environmental temperatures were almost similar to those for common carp reported previously.

Correlation with larval body size of mRNA levels of growth hormone, growth hormone receptor I and insulin-like growth factor I in larval torafugu Takifugu rubripes.

The full-length of insulin-like growth factor (IGF) complementary (c)DNAs encoded by igf-I and igf-II from torafugu pufferfish Takifugu rubripes were cloned in the present study. The deduced amino acid sequences of the two genes showed c. 80% identity each with those of Igf-I and Igf-II from other teleosts, respectively. Two growth hormone (GH) receptors, ghr1 and ghr2, were also cloned in silico using the T. rubripes Fugu genome database. The transcripts of T. rubripes igf-I were detected in slow muscle, heart, skin, gill, liver and intestine but not in fast muscle, spleen and testis of adult fish, whereas those of igf-II were found in all tissues examined. Subsequently, the accumulated messenger (m)RNA levels of igf-I and igf-II were investigated in an F(2) population derived from a male of an apparent fast-growing T. rubripes strain and a wild female T. rubripes together with those of other growth-related genes encoding Gh, Ghr1 and Ghr2, and with those of prolactin (Prl) and leptin (Lep) previously reported. The accumulated mRNA levels of igf-I, gh and ghr1 were significantly correlated to growth rate at larval stages in the population, but not for those of igf-II, prl, ghr2 and lep. Although it is unclear whether or not this phenotype is directly related to the heredity of the fast-growing strain, the findings suggest that the expression of igf-I, gh and ghr1 is involved in the regulation of growth rate at larval stages in T. rubripes.

Stomach Chitinase from Japanese Sardine Sardinops melanostictus: Purification, Characterization, and Molecular Cloning of Chitinase Isozymes with a Long Linker

Fish express two different chitinases, acidic fish chitinase-1 (AFCase-1) and acidic fish chitinase-2 (AFCase-2), in the stomach. AFCase-1 and AFCase-2 have different degradation patterns, as fish efficiently degrade chitin ingested as food. For a comparison with the enzymatic properties and the primary structures of chitinase isozymes obtained previously from the stomach of demersal fish, in this study, we purified chitinase isozymes from the stomach of Japanese sardine Sardinops melanostictus, a surface fish that feeds on plankton, characterized the properties of these isozymes, and cloned the cDNAs encoding chitinases. We also predicted 3D structure models using the primary structures of S. melanostictus stomach chitinases. Two chitinase isozymes, SmeChiA (45 kDa) and SmeChiB (56 kDa), were purified from the stomach of S. melanostictus. Moreover, two cDNAs, SmeChi-1 encoding SmeChiA, and SmeChi-2 encoding SmeChiB were cloned. The linker regions of the deduced amino acid sequences of SmeChi-1 and SmeChi-2 (SmeChi-1 and SmeChi-2) are the longest among the fish stomach chitinases. In the cleavage pattern groups toward short substrates and the phylogenetic tree analysis, SmeChi-1 and SmeChi-2 were classified into AFCase-1 and AFCase-2, respectively. SmeChi-1 and SmeChi-2 had catalytic domains that consisted of a TIM-barrel (β/α)8–fold structure and a deep substrate-binding cleft. This is the first study showing the 3D structure models of fish stomach chitinases.

Changes in rheological properties of grass carp fast skeletal myosin induced by seasonal acclimatization

To elucidate the effects of seasonal temperature acclimatization on thermal gelation of grass carp myosin, myosins from fish in different seasons were prepared and investigated for the changes in dynamic viscoelastic parameters including storage modulus (G′), loss modulus (G″) and damping factor (tan δ) upon heating. Myosins from fish in spring and summer had a temperature region of 38–44°C for the first marked increase of G′ higher than that of myosins from fish in autumn and winter (28–33°C). The measurement temperature-dependent changes in dynamic viscoelastic parameters such as G″ and tan δ were also different among the four myosins. While gel formation was observed with the spring and summer myosins, apparently in two steps, three steps were found in the autumn myosin. Furthermore, the winter myosin exhibited more than three steps for gel formation. These differences in rheological properties among the four myosins were considered to be attributed to the differences in thermodynamic and structural properties of these myosins previously reported.

Effects of Chilled Storage, Freezing Rates, and Frozen Storage Temperature on Lipid Oxidation in Meat Blocks from Cultured Bluefin Tuna Thunnus thynnus

ABSTRACT The effects of a short chilled storage period before freezing, frozen storage temperature, and freezing rate on lipid oxidation of bluefin tuna (Thunnus thynnus) meat during frozen storage were investigated. After 12-months storage, all samples had increased in peroxide value though they were less at the lower temperatures (−45 and −60°C). Peroxide values in all samples stored at −20°C increased after 3 months storage, particularly those processed and stored 51 h after harvest. The lowest increase in peroxide value occurred in the samples frozen rapidly 3 h after harvest. Vitamin E levels decreased faster during frozen storage at −20°C. There were no apparent differences in levels of triacylglycerides nor in n-3 fatty acid levels between treatments, storage periods, and storage temperatures. After 12-months storage, headspace oxidative volatiles were highest in samples stored at −20°C and lowest in those stored at −60°C. Lipid oxidation in tuna meat stored at −45°C is similar to that at −60°C, and rapid freezing rather than slow freezing should be used.

cDNA cloning and complete primary structures of myosin heavy chains from brushtooth lizardfish Saurida undosquamis and wanieso lizardfish S. wanieso fast skeletal muscles

The complete cDNA sequences encoding predominant types of myosin heavy chain (MYH) in the fast skeletal muscle were, determined for brushtooth lizardfish Saurida undosquamis and wanieso lizardfish S. wanieso, which are used as materials for preparing high-quality surimi-based products. The cDNA consisted of 5973 and 5987 bp, respectively, and both encompassed an open reading frame encoding a polypeptide of 1936 amino acid residues. Brushtooth and wanieso lizardfish MYH showed the amino acid, sequence identity of 92–93% to white croaker MYH, which was higher than that of 90% to walleye pollack MYH. The putative binding sites for ATP, actin, and regulatory and essential light chains in the subfragment-1 region of brushtooth lizardfish MYH exhibited a high identity with white croaker counterparts as well as the sequences of subfragment-2 and light meromyosin. In contrast, phylogenetic tree, constructed by the neighbor-joining method based on mitochondrial 16S rRNA gene, revealed that the two lizardfish species formed a cluster with walleye pollack, which was paraphyletic with white croaker. Therefore, a good reputation for lizardfish and white croaker to have a high thermal-gel forming ability seemed to be reflected by MYH rather than biolgoical similarity as revealed by the mitochondrial 16S rRNA gene.