Journal
BIOSCIENCE BIOTECHNOLOGY AND BIOCHEMISTRY
Volume 64, Issue 8, Pages 1656-1663Publisher
OXFORD UNIV PRESS
DOI: 10.1271/bbb.64.1656
Keywords
Chlorella vulgaris C-27; cryoprotection; freezing tolerance; LEA protein
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The nucleotide sequence of hiC12, isolated as a cDNA clone of hardening-induced Chlorella (hiC) genes, was identified. The clone encodes a late embryogenesis abundant (LEA) protein having six repeats of a Il-mer amino acid motif, although in a slightly imperfect form. To overexpress the hiC6(1)) and hiC12 genes, their coding regions were PCR amplified and subcloned into a pGEX-1 lambda T vector. The HIC6 and HIC12 proteins were expressed as GST fusion proteins in E. coli, then purified. The two HIC proteins were found to be effective in protecting a freeze-labile enzyme, LDH, against freeze-inactivation, On a molar concentration basis, they were about 3.1 x 10(6) times more effective in protecting LDH than sucrose and as effective as BSA. Cryoprotection tests with five kinds of chain-shortened polypeptides, synthesized based on the Il-mer amino acid motif of the HIC6 protein showed that the cryoprotective activity decreased with a decrease in the repeating units of the Il-mer motif. In fact, cryoprotective activities of three kinds of single Il-mer amino acids were very low even at high concentrations. All the results suggested that the sufficiently repeated Il-mer motif is required for the cryoprotective activities of Chlorella LEA proteins.
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