Biochemical and molecular characterization and expression of the 11S-type storage protein from Coffea arabica endosperm

In order to define better the endosperm protein content of commercial coffe e species Coffea arabica (Arabica) and C. canephora (Robusta), the principa l storage protein of coffee grains has been analysed by 2-dimensional elect rophoresis (2DE) and amino acid microsequencing. The most abundant polypept ide spots observed on mature coffee grain 2DE profiles were found to be sub units of the same protein, which exists as multiple isoforms with varying p Is. Strong sequence similarity was found to the 11S family of plant storage proteins. The structure is typical of the 11S type, which occurs as a prec ursor of 55 kDa, and is observed under denaturing and reducing conditions o n 2DE profiles in the form of cleavage products at approximately 20 kDa (be ta arms) and 32 kDa (alpha arms). Differences between Arabica and Robusta 2 DE profiles indicate a secondary 11S protein family in some varieties of th e latter. The existence of multiple pi forms may indicate that a multigene family encodes for these proteins. We estimate that the protein accounts fo r approximately 45% of total grain protein. A cloned full-length cDNA of 1 706 bp coding for one of the isoforms is described and discussed in relatio n to other coffee storage protein sequences. (C) Elsevier, Paris.