Structural Relationships of 7S and 11S Globulins

Abstract

It is now well recognized that an understanding of protein structure is fundamental to a proper understanding of protein function, and from this perspective the above quotation from Osborne’s text “The Vegetable Proteins” remains a succinct description of our structural understanding of storage proteins even today. Indeed, it should be recalled that legume storage proteins were first isolated in the latter half of the last century, and that some of these proteins could be obtained in crystalline form. Of course that was prior to the discovery of X-rays and high-resolution structural determination of these proteins could not be contemplated. Now, a full century later, detailed structural information is available for only two globulins, namely the closely-related 7S proteins from P. vulgaris (phaseolin, Lawrence et al., 1990, 1994) and C. ensiformis (canavalin. Ko et al. 1993a, b). There remains no high-resolution detail for any member of the 11S family, despite preliminary crystallographic analysis of the respective 11S proteins of sesame (Hasegawa et al., 1978), pumpkin (Hara et al., 1976; Colman et al., 1980), tobacco (Drenth and Wiebenga, 1955), Brazil nut (Drenth and Wiebenga, 1955; Kamiya et al., 1983), hemp (Drenth and Wiebenga. 1955; Patel et al., 1994) and coconut (Carr et al., 1990). The crystals employed in these studies vary considerably in quality and none has yet led to any information at the atomic level. As a consequence, buoyed by the ever-increasing amount of primary sequence data, renewed effort has been made to investigate structural relationships between the 7S and US proteins (Argos et al., 1985; Wright, 1988; Gibbs et al. 1989; Lawrence et al., 1994; Bäumlein et al., 1995; Shutov et al., 1995).

Although the proteins of plants early claimed the attention of many chemists, our present knowledge of them has not yet advanced beyond what is, in fact, a mere beginning of a serious study. Osborne (1909).