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 famil ies, lipid transfer proteins (nsLTP) and indolines have been isolated from cereal kernels. NsLTPs are basic proteins, stabilised by four intramolecula r disulphide bonds and with molecular masses of 9 kDa (nsLTP1) and 7 kDa (n sLTP2). 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 hydrop hobic cutin and suberin lavers which prevent water diffusion into the grain and fungal attacks. Furthermore some nsLTPs display anti-microbial activit y in vitro. In brewing, barley nsLTP1, and especially its unfolded and glyc osylated forms, control the formation of beer foam. Indolines are basic lip id binding proteins with a molecular mass around 13 kDa and five disulphide bonds. Their lipid binding site is composed by an unique tryptophan-rich d omain. Although their 3D structure has not been determined, secondary struc ture and cysteine pairings suggest that indolines and nsLTP1s share similar folding characteristics. The biological role of these seed specific protei ns is not known. Indolines are capable of synergistically enhancing the ant ifungal properties of thionins. in vitro. In their native stale, indolines display good foaming properties and prevent protein foams from destabilisat ion by lipids. In breadmaking these proteins interfere both in dough rheolo gy and in bread crumb texture. Puroindolines are also the main components o f friabilins, proteins found at the surface of starch granules of soft whea ts. Although their role in grain hardness is still obscure. their encoding genes are obviously useful for exploring the Hardness locus and manipulatin g grain hardness. (C) 2000 Academic Press.