Crystal structure of nonspecific lipid transfer protein from Solanum melongena

Lipids are considered to protect protein allergens from proteolysis and are generally seen to exist in a bound form. One of the well-known plant protein families with bound lipids is non-specific lipid transfer proteins (nsLTPs). Structure-function relationships in the case of the members of non-specific lipid transfer protein family are not clearly understood. As part of exploring the seed proteome, we have analyzed the proteome of a member of Solanaceae family, Solanum melongena (eggplant) and a non-specific lipid transfer protein from S. melongena, SM80.2 was purified, crystallized and the structure was determined at 1.87 Å resolution. Overall, the tertiary structure is a cluster of α-helices forming an internal hydrophobic cavity. Absence of conserved Tyr79, known to govern the plasticity of hydrophobic cavity, and formation of hydrogen bond between Asn79 and Asn36 further reduced the pocket size. Structural analysis of SM80.2 thus gives insight about a new hydrogen bond mediated mechanism followed in closure of the binding pocket. Extra electron densities observed at two different places on the protein surface and not in the cavity could provide interesting physiological relevance. In light of allergenic properties, probably overlapping of epitopic region and ligand binding on surface could be a main reason. This work shows first crystal structure of A-like nsLTP with a close binding pocket and extra density on the surface suggesting a plausible intermediate state during transfer.