Zeolin. A new recombinant storage protein constructed using maize gamma-zein and bean phaseolin

The major seed storage proteins of maize (Zea mays) and bean (Phaseolus vulgaris), zein and phaseolin, accumulate in theendoplasmic reticulum (ER) and in storage vacuoles, respectively.We show here that a chimeric protein composed of phaseolinand 89 amino acids of g-zein, including the repeated and the Pro-rich domains, maintains the main characteristics of wild-typeg-zein: It is insoluble unless its disulfide bonds are reduced and forms ER-located protein bodies. Unlike wild-type phaseolin,the protein, which we called zeolin, accumulates to very high amounts in leaves of transgenic tobacco (Nicotiana tabacum). Arelevant proportion of the ER chaperone BiP is associated with zeolin protein bodies in an ATP-sensitive fashion. Pulse-chaselabeling confirms the high affinity of BiP to insoluble zeolin but indicates that, unlike structurally defective proteins that alsoextensively interact with BiP, zeolin is highly stable. We conclude that the g-zein portion is sufficient to induce the formation ofprotein bodies also when fused to another protein. Because the storage proteins of cereals and legumes nutritionallycomplement each other, zeolin can be used as a starting point to produce nutritionally balanced and highly stable chimericstorage proteins.