Structure, biological and technological functions of lipid transfer proteins and indolines, the major lipid binding proteins from cereal kernels

Using specific extraction procedures, two major lipid binding protein families, lipid transfer proteins (nsLTP) and indolines have been isolated from cereal kernels. NsLTPs are basic proteins, stabilised by four intramolecular disulphide bonds and with molecular masses of 9 kDa (nsLTP1) and 7 kDa (nsLTP2). The 3D structures of nsLTP1 from barley maize, rice and wheat seeds have been determined. Within the protein a large hydrophobic tunnel forms the lipid binding site. NsLTPs could be involved in the formation of hydrophobic cutin and suberin lavers which prevent water diffusion into the grain and fungal attacks. Furthermore some nsLTPs display anti-microbial activity in vitro. In brewing, barley nsLTP1, and especially its unfolded and glycosylated forms, control the formation of beer foam. Indolines are basic lipid binding proteins with a molecular mass around 13 kDa and five disulphide bonds. Their lipid binding site is composed by an unique tryptophan-rich domain. Although their 3D structure has not been determined, secondary structure and cysteine pairings suggest that indolines and nsLTP1s share similar folding characteristics. The biological role of these seed specific proteins is not known. Indolines are capable of synergistically enhancing the antifungal properties of thionins. in vitro. In their native stale, indolines display good foaming properties and prevent protein foams from destabilisation by lipids. In breadmaking these proteins interfere both in dough rheology and in bread crumb texture. Puroindolines are also the main components of friabilins, proteins found at the surface of starch granules of soft wheats. Although their role in grain hardness is still obscure. their encoding genes are obviously useful for exploring the Hardness locus and manipulating grain hardness. (C) 2000 Academic Press.