Comparison of functional properties of two fungal antifreeze proteins from Antarctomyces psychrotrophicus and Typhula ishikariensis

Abstract

Antifreeze proteins are structurally diverse polypeptides that have thermal hysteresis activity and have been discovered in many cold-adapted organisms. Of these, fungal antifreeze protein has been purified and partially characterized only in a species of psychrophilic basidiomycete, Typhula ishikariensis. Here we report a new fungal antifreeze protein from another psychrophile, Antarctomyces psychrotrophicus. We examined its biochemical properties and thermal hysteresis activity, and compared them with those of the T. ishikariensis antifreeze protein. The antifreeze protein from A. psychrotrophicus was purified and identified as an extracellular protein of approximately 28 kDa, which halved in size following digestion with glycosidase. The A. psychrotrophicus antifreeze protein generated bipyramidal ice crystals and exhibited thermal hysteresis activity (for example thermal hysteresis = 0.42 degrees C for a 0.48 mM solution) similar to that of fish antifreeze proteins, while a unique rugged pattern was created on the facets of the ice bipyramid. The thermal hysteresis activity of the A. psychrotrophicus antifreeze protein was maximized under alkaline conditions, while that of the T. ishikariensis antifreeze protein was greatest under acidic conditions. The T. ishikariensis antifreeze protein exhibited a bursting ice growth normal to the c-axis of the ice crystal and high thermal hysteresis activity (approximately 2 degrees C), as in the case of insect hyperactive antifreeze proteins. From these results, we speculate that the A. psychrotrophicus antifreeze protein is very different from the T. ishikariensis antifreeze protein, and that these two psychrophiles have evolved from different genes.

Ice-binding site of snow mold fungus antifreeze protein deviates from structural regularity and high conservation

“…X-ray diffraction data were collected to 0.95-Å resolution at −173°C on BL44B2 at the SPring-8. The electron density map showed one-to-one correspondence with the amino acid sequence of TisAFP6, thereby showing that only TisAFP6 had only been crystallized out of the the mixture of isoforms (25). The crystallographic R factor and free R factor of the final structure were 0.112 and 0.129, respectively.…”

“…The snow mold fungus, Typhula ishikariensis, attaches onto dormant plants and secretes its AFP (TisAFP) toward the extracellular space under snow cover (25). Purified TisAFP is a mixture of 223-residue polypeptide isoforms.…”

A novel dehydrin-like protein from Aspergillus fumigatus regulates freezing tolerance

“…AFPs are extracellular polypeptides that depress the freezing point of water and modify the structure of ice crystals. They have been described in cold-adapted organisms, among which the basidiomycetes Coprinus psychromorbidus (Hoshino et al, 2003a) and Typhula ishikariensis (Hoshino et al, 2003b) and the ascomycete Antarctomyces psychrotrophicus (Xiao et al, 2010). Blast against Aspergillus genomes did not give any hit.…”

Marine Antifreeze Proteins: Structure, Function, and Application to Cryopreservation as a Potential Cryoprotectant

“…Only two mushrooms (enoki and shiitake), one snow mold fungus ( Typhula ishikariensis ), and two yeast organisms ( Glaciozyma antarctica and Glaciozyma sp. AY30) have been characterized both genomically and for their antifreeze properties [9,10,140,141]. …”