A multigene family of trypsin/a-amylase inhibitors from cereals

Abstract

Plant proteinaceous inhibitors of hydrolases from heterologous systems (fungi, insects, vertebrates, etc.) have been extensively studied. Recent advances in the molecular biology of these inhibitors have greatly increased our knowledge of their structure and in vitro properties, and have allowed previously unsuspected relationships between functionally different proteins to be established. In wheat and barley, a substantial fraction of the total endosperm protein content is represented by toxins and inhibitors that are active towards heterologous systems. In these cereals, a single protein family of trypsin/aamylase inhibitors is prominently represented among albumins and globulins from endosperm. More than 20 different members from this family have been characterized (reviewed by Carbonero et ai, 1993; García-Olmedo et -ai.9 1987; 1992). Their apparent molecular weights are in the 12-16,000 range, and some of them can be selectively extracted with chloroform/methanol mixtures and have therefore been designated CM-proteins. The a-amylase inhibitors can be classified according to their degree of aggregation into monomeric, dimeric, and tetrameric forms. The trypsin inhibitors are monomeric. No members of this family have been found in tissues other than endosperm, although this aspect deserve further investigation. During kernel development, their synthesis precedes that of the main storage proteins and they are rapidly degraded upon germination. These inhibitors have been found not only in wheat and barley but also in other species of the Poaceae (Gramineae) such as rye, rice, maize and finger-millet (Carbonero et al., 1993; García-Olmedos a/., 1987; 1992).