Hidehisa Kawahara

The Structures and Functions of Ice Crystal-Controlling Proteins from Bacteria.

Many organisms have evolved into unique mechanisms which minimize freezing injury due to extracellular ice formation. Specifically, certain bacteria have produced a few proteins each with different functions. For example, the ice nucleation protein acts as a template for ice formation, which is responsible for imparting ice nucleating activity. The anti-nucleating protein inhibits the fluctuation of ice nucleus formation by a foreign particle in the water drop. Also, the antifreeze proteins depress the freezing temperature, modify or suppress ice crystal growth, inhibit ice recrystallization, and protect the cell membrane from cold-induced damage. In this article, a review on the current knowledge of the structure and the function of these three types of proteins, which are capable of interacting with ice itself or its nuclei from bacteria.

Cloning and Expression of afpA, a Gene Encoding an Antifreeze Protein from the Arctic Plant Growth-Promoting Rhizobacterium Pseudomonas putida GR12-2

The Arctic plant growth-promoting rhizobacterium Pseudomonas putida GR12-2 secretes an antifreeze protein (AFP) that promotes survival at subzero temperatures. The AFP is unusual in that it also exhibits a low level of ice nucleation activity. A DNA fragment with an open reading frame encoding 473 amino acids was cloned by PCR and inverse PCR using primers designed from partial amino acid sequences of the isolated AFP. The predicted gene product, AfpA, had a molecular mass of 47.3 kDa, a pI of 3.51, and no previously known function. Although AfpA is a secreted protein, it lacked an N-terminal signal peptide and was shown by sequence analysis to have two possible secretion systems: a hemolysin-like, calcium-binding secretion domain and a type V autotransporter domain found in gram-negative bacteria. Expression of afpA in Escherichia coli yielded an intracellular 72-kDa protein modified with both sugars and lipids that exhibited lower levels of antifreeze and ice nucleation activities than the native protein. The 164-kDa AFP previously purified from P. putida GR12-2 was a lipoglycoprotein, and the carbohydrate was required for ice nucleation activity. Therefore, the recombinant protein may not have been properly posttranslationally modified. The AfpA sequence was most similar to cell wall-associated proteins and less similar to ice nucleation proteins (INPs). Hydropathy plots revealed that the amino acid sequence of AfpA was more hydrophobic than those of the INPs in the domain that forms the ice template, thus suggesting that AFPs and INPs interact differently with ice. To our knowledge, this is the first gene encoding a protein with both antifreeze and ice nucleation activities to be isolated and characterized.

Identification of an antifreeze lipoprotein from Moraxella sp. of Antarctic origin.

We found six bacteria capable of producing antifreeze protein (AFP) from Ross Island, Antarctica. Among these AFP-producing bacteria, strain No. 82 had the highest antifreeze activity and was identified as Moraxella sp. The optimum temperature and pH for the production of AFP were 5°C and 7.0, respectively. After partially purifying the AFP from the culture supernatant using 60% saturation of ammonium sulfate, only the 52-kDa protein band (100 μg/ml) which eluted from SDS-PAGE indicated antifreeze activity by the formation of hexagonal crystals. Furthermore, we confirmed that this AFP was a lipoprotein by the lipid stain test and treatment with some enzymes and that it had no ice-nucleating activity. Also, the N-terminal amino acid sequence of this AFP had high similarity with that of outer membrane proteins from Moraxella (Branhamella) catarrhalis. This is the first report of AFP-producing bacteria in Antarctica and an antifreeze lipoprotein (AFLP) from Moraxella sp.

Involvement of SIK3 in Glucose and Lipid Homeostasis in Mice

Salt-inducible kinase 3 (SIK3), an AMP-activated protein kinase-related kinase, is induced in the murine liver after the consumption of a diet rich in fat, sucrose, and cholesterol. To examine whether SIK3 can modulate glucose and lipid metabolism in the liver, we analyzed phenotypes of SIK3-deficent mice. Sik3 −/− mice have a malnourished the phenotype (i.e., lipodystrophy, hypolipidemia, hypoglycemia, and hyper-insulin sensitivity) accompanied by cholestasis and cholelithiasis. The hypoglycemic and hyper-insulin-sensitive phenotypes may be due to reduced energy storage, which is represented by the low expression levels of mRNA for components of the fatty acid synthesis pathways in the liver. The biliary disorders in Sik3 −/− mice are associated with the dysregulation of gene expression programs that respond to nutritional stresses and are probably regulated by nuclear receptors. Retinoic acid plays a role in cholesterol and bile acid homeostasis, wheras ALDH1a which produces retinoic acid, is expressed at low levels in Sik3 −/− mice. Lipid metabolism disorders in Sik3 −/− mice are ameliorated by the treatment with 9-cis-retinoic acid. In conclusion, SIK3 is a novel energy regulator that modulates cholesterol and bile acid metabolism by coupling with retinoid metabolism, and may alter the size of energy storage in mice.

A Potent Inhibitor of SIK2, 3, 3′, 7-Trihydroxy-4′-Methoxyflavon (4′-O-Methylfisetin), Promotes Melanogenesis in B16F10 Melanoma Cells

Flavonoids, which are plant polyphenols, are now widely used in supplements and cosmetics. Here, we report that 4′-methylflavonoids are potent inducers of melanogenesis in B16F10 melanoma cells and in mice. We recently identified salt inducible kinase 2 (SIK2) as an inhibitor of melanogenesis via the suppression of the cAMP-response element binding protein (CREB)-specific coactivator 1 (TORC1). Using an in vitro kinase assay targeting SIK2, we identified fisetin as a candidate inhibitor, possibly being capable of promoting melanogenesis. However, fisetin neither inhibited the CREB-inhibitory activity of SIK2 nor promoted melanogenesis in B16F10 melanoma cells. Conversely, mono-methyl-flavonoids, such as diosmetin (4′-O-metlylluteolin), efficiently inhibited SIK2 and promoted melanogenesis in this cell line. The cAMP-CREB system is impaired in Ay/a mice and these mice have yellow hair as a result of pheomelanogenesis, while Sik2+/−; Ay/a mice also have yellow hair, but activate eumelanogenesis when they are exposed to CREB stimulators. Feeding Sik2+/−; Ay/a mice with diets supplemented with fisetin resulted in their hair color changing to brown, and metabolite analysis suggested the presence of mono-methylfisetin in their feces. Thus, we decided to synthesize 4′-O-methylfisetin (4′MF) and found that 4′MF strongly induced melanogenesis in B16F10 melanoma cells, which was accompanied by the nuclear translocation of TORC1, and the 4′-O-methylfisetin-induced melanogenic programs were inhibited by the overexpression of dominant negative TORC1. In conclusion, compounds that modulate SIK2 cascades are helpful to regulate melanogenesis via TORC1 without affecting cAMP levels, and the combined analysis of Sik2+/− mice and metabolites from these mice is an effective strategy to identify beneficial compounds to regulate CREB activity in vivo.

Production of two types of ice crystal-controlling proteins in Antarctic bacterium.

Pseudomonas fluorescens KUAF-68, which was isolated from Antarctica, had both ice-nucleating protein and antifreeze protein activities in the culture broth. We found that both proteins were separately produced based on the results of column chromatography, SDS-PAGE analysis and Southern hybridization. The activity of the ice-nucleating protein was stimulated by the addition of glycine (0.020 N%), whereas the activity of the antifreeze protein was stimulated by the addition of L-asparagine (0.025 N%). This is the first report on the production of two types of ice crystal-controlling proteins in one bacterial strain.

Type II antifreeze protein from a mid-latitude freshwater fish, Japanese smelt (Hypomesus nipponensis).

A lot of reports of antifreeze protein (AFP) from fish have been published, but no report has mentioned of commercialized mid-latitude fresh water fish which producing AFP in its body fluid. We found that the AFP in the body fluid of Japanese smelt (Hypomesus nipponensis) from mid-latitude fresh water was purified and characterized. The N-terminal amino acid sequence of the Japanese smelt AFP was 75.0% identical to Type II AFP from herring. Results of EDTA treatment and ruthenium red staining suggested that the Japanese smelt AFP had at least one Ca2+-binding domain. Interestingly, the antifreeze activity of the Japanese smelt AFP did not completely disappear when Ca2+ ions were removed. The molecular mass of the Japanese smelt AFP was calculated to be 16,756.8 by the TOF-mass analysis. The Open reading flame of the gene coding for the Japanese smelt AFP was 444 bp long and was 85.0% identical with the entire herring AFP gene. The cDNA and amino acid sequence of the Japanese smelt AFP were the same length as those of herring AFP.

Identification of a novel anti-ice-nucleating polysaccharide from Bacillus thuringiensis YY529.

Strain YY529, capable of producing some anti-ice-nucleating materials (ANM), was isolated from the surface of a camphor leaf. Strain YY529 was identified as Bacillus thuringiensis from its characteristics and taxonomy; the optimum temperature and pH for producing these ANMs were 30°C and 7.0, respectively. One of the ANM with the highest activities among them was purified from the culture. The molecular weight of the ANM was approximately 130 kDa based on a gel filtration analysis. We confirmed that this ANM was a polysaccharide based on the results of the treatment with a mannosidase and the molish reaction. In addition, the LCMS analysis showed that this anti-ice-nucleating polysaccharide (ANPS) had the polyacetyl-D-glucosamine moiety in its structure. Furthermore, this ANPS showed its ability as a non-freeze agent in a preservative solution for the cryopreservation of cock liver. This is the first report of ANPS as a novel ANM from Bacillus thuringiensis YY529.

Relationship Between Antifreeze Protein and Freezing Resistance in Pseudomonas putida GR12-2

Following transposon Tn5 mutagenesis of the plant growth-promoting rhizobacterium Pseudomonas putida GR12-2, mutants that have different freeze-resistant properties were selected. Five of the freeze-sensitive mutants, i.e. FSM-5, -6, -14, -29, and -41, secreted a lower amount of antifreeze protein-(AFP) into the culture broth compared with the wild-type. Among of these five mutants, the three mutants (FSM-6, FSM-14, and FSM-41) that have the lowest level of freezing resistance (4.0–6.0% survival) also produce AFP at low levels (0.5–0.9 μg/mL) compared with the wild-type (4.8 μg/ml). The antifreeze and ice-nucleating activities of the AFP from these three mutant strains were similar to those of wild-type. Furthermore, the decreased freezing resistance from three mutants could be partially restored by adding purified AFP to mutant cell suspensions. Freezing resistance of three mutants was found to increase in proportion to the addition of AFP up to a concentration of 50 μg/mL. We conclude that accumulation of AFP is one component of the mechanism for freezing resistance in bacteria.

Properties of cell-free ice nuclei from ice nucleation-active Pseudomonas fluorescens KUIN-1

Abstract The properties of cell-free ice nuclei (CFIN) from ice nucleation-active Pseudomonas fluorescens KUIN-1 were investigated. CFIN were found to be present in the culture supernatant liquid and were separated from P. fluorescens KUIN-1 by centrifugation, filtration (0.22 μm, pore size) and ultrafiltration. Sucrose was a good carbon source for the ice-nucleating activity of CFIN and l -sodium glutamate was a good nitrogen source. In an ice-nucleating medium in 1 l of water, maximum growth was obtained with production of 118 mg of CFIN at 18°C after 48 h with shaking. The ice-nucleating activity was greatly decreased by treating CFIN at 40°C for 30 min and was completely lost by heating at 90°C. The ice-nucleating activity of CFIN was inhibited by the addition of protease K, thermolysin or lipase. However, phospholipase A2 had no effect. The freezing difference spectra in D2O-H2O for CFIN were similar to the freezing difference spectra in D2O-H2O for the cells. Consequently, it could be inferred that there were three types of nucleating activity on CFIN. CFIN active at −3.2∼−4.3°C, −4.5 to −6.1°C or >−8.1°C were arbitrarily assigned into three groups—class A, class B or class C.