Purification and N-terminal sequence analysis of 60 and 31kDa fruit-specific proteins from Apple(Malus domestica cv. Fuji)

Abstract

To investigate the protein profile of apple(Malus domestica cv. Fuji) fruit and isolate apple fruit-specific proteins, total proteins of apple leaf and fruit of the breaker stage were compared by SDS-PAGE(Sodium dodacyl sulfate polyacrylamide gel electrophoresis) Four major protein spots were found to be expressed in a fruit-specific manner and two of them, protein A and C, 60kDa and 31kDa respectively, were purified and their N-terminal sequences determined. Protein C was identified as the same protein with a 31 kDa major allergen/disease resistance protein homolog. It also had homology with variety of thaumatin-like proteins, a group of pathogenesis-related proteins from various plant species. The existence of thaumatin-like proteins in many other ripening fruits was reported, suggesting that this group of proteins play a role in fruit ripening, not only the defence role to pathogen infections. The partial peptide sequence of protein A, the most abandunt protein from ripening apple fruit had no homology with known protein. A DNA probe was synthesized by PCR for the cloning of the gene encoding protein A.