Conserved amino acid sequences among plant proteins sorted to protein bodies and plant vacuoles. Can they play a role in protein sorting?

Amino acid sequence comparisons were made between the soybean alpha subunit of beta-conglycinin and 34 members of different plant protein families targeted to seed protein bodies or vacuoles. A number of short conserved amino acid sequences were identified in seed storage proteins, plant protease inhibitors and lectins, and the probable functions of these sequences are discussed. For proteins of known tertiary structure, these sequences map to the surface of the respective molecules. It is postulated that these regions produce a common secondary structure which could interact with other molecules involved in the sorting process. One of these regions, region A, is similar to the yeast carboxypeptidase Y (CPY) vacuolar targeting signal, and is present in both storage proteins and lectins. Computer modeling based upon the tertiary structure of concanavalin A (ConA) was used to generate models representing the structure of two highly related lectins from Dolichos biflorus, one of which is targeted to protein bodies and the other secreted. A different glycosylation pattern together with amino acid sequences upstream of the identified conserved amino acid sequences are predicted to modulate the presentation of the sorting domains in the lectins and be the determinant in the sorting of these lectins.