Structure of a liganded type 2 non-specific lipid-transfer protein from wheat and the molecular basis of lipid binding

Abstract

In plants, a family of ubiquitous proteins named non-specific lipid-transfer proteins (ns-LTPs) facilitates the transfer of fatty acids, phospholipids and steroids between membranes. Recent data suggest that these secreted proteins play a key role in the formation of cuticular wax layers and in defence mechanisms against pathogens. In this study, X-ray crystallography has been used to examine the structural details of the interaction between a wheat type 2 ns-LTP and a lipid, L-alpha-palmitoyl-phosphatidyl glycerol. This crystal structure was solved ab initio at 1.12 A resolution by direct methods. The typical alpha-helical bundle fold of this protein is maintained by four disulfide bridges and delineates two hydrophobic cavities. The inner surface of the main cavity is lined by non-polar residues that provide a hydrophobic environment for the palmitoyl moiety of the lipid. The head-group region of this lipid protrudes from the surface and makes several polar interactions with a conserved patch of basic residues at the entrance of the pocket. The alkyl chain of a second lipid is bound within an adjacent smaller cavity. The structure shows that binding of the lipid tails to the protein involves extensive hydrophobic interactions.

The biochemistry and biology of extracellular plant lipid‐transfer proteins (LTPs)

“…Structures have only been solved for an LTP2 from rice (Samuel et al 2002) and the LTP2 from wheat in complex with L-a-palmitoyl-phosphatidyl glycerol (Pons et al 2003;Hoh et al 2005). Family 2 LTPs also have four helices bound by four disulfide bonds enclosing a hydrophobic lipid binding cavity (Fig.…”

“…However, the pairing partners of cysteines 5 and 6 (CXC) are switched: In family 1 LTPs, C5 forms a disulfide with C8 and C6 with C1, while in family 2 LTPs, C5 forms a disulfide with C1 and C6 bonds with C8 (Cheng et al 2004a). Although smaller than the hydrophobic cavity of LTP1s, the cavity of family 2 LTPs is more flexible, allowing for the accommodation of a wider variety of lipids, including sterols (Samuel et al 2002;Pons et al 2003;Cheng et al 2004a;Hoh et al 2005).…”

Barley Grain Non-specific Lipid-Transfer Proteins (ns-LTPs) in Beer Production and Quality

“…Compared with ns-LTP1, ns-LTP2 cysteine pairing has a one miss match motif 40 . The three-dimensional structures of unliganded rice grain ns-LTP2 128 and wheat grain ns-LTP2 liganded with L-␣-palmitolylphosphatidylglycerol 70,120 have been resolved. Wheat ns-LTP2, whose sequence shows ∼77% identity with barley grain ns-LTP2, is composed of five helices, structured as a right superhelix 120 .…”

“…8) flexible enough to bind linear molecules 70 as well as large ones with a rigid structure, such as sterols 26 . According to Hoh et al 70 , besides a main hydrophobic cavity capable of accommodating a broad range of fatty acids (10-18 C atoms), ns-LTP2 possesses within its structure a secondary, smaller cavity able to accommodate shorter fatty acids (8-14 C atoms).…”

“…A most remarkable feature of their structure is the existence of an inner hydrophobic cavity capable of accommodating various lipids and hydrophobic molecules 65,120 . The difference in the hydrophobic cavity dimension and profile between ns-LTP1 26,70 . The biological role of ns-LTPs has for a long time been puzzling 81 and the last few decades witnessed excessive scientific efforts to reveal relationships between ns-LTPs structure, lipid-binding ability and biological role 19 .…”