A low temperature induced apoplastic protein isolated from Arachis hypogaea

We describe the isolation, characterization and identification of an Arachis hypogaea cold shock protein (AHCSP33). AHCSP33 is secreted into the leaf apoplast during low temperature exposure. N-terminal sequence of AHCSP33 shows homology to Thaumatin-Like (TL) protein family (also called Group5 Pathogenesis-related (PR) proteins). AHCSP33 shows strongest homology (55%) at the N-terminus with the Rye TL protein (M(r) 25 k) which is an apoplastic protein and has antifreeze activity. Like several TL proteins, AHCSP33 is also targeted to the apoplast and persists for several days after low temperature treatment, although at reduced levels. AHCSP33 possesses intrachain disulfide bonds which is a well conserved feature of TL proteins. AHCSP33 might be involved in cryoprotecting proteins as it was shown to prevent freeze-induced denaturation of L-lactate dehydrogenase (LDH). Several features of AHCSP33 are consistent with its role in cryoprotection. It is a hydrophilic protein and is boiling stable. Hydrophilic amino acids constitute 80.4 mol%. Asp/Asn and Glu/Gln together constitute 20.8 mol%. AHCSP33 is glycosylated and exists as an oligomer in its native state.