Structural study of novel lipid-dependent dimerization of human GLTP induced by point mutation
- Dr. Valeriya SAMYGINA
- Dr. Valeriya SAMYGINA (FSRC "Crystallography and Photonics" RAS, NRC "Kurchatov Institute", Structural Biology Unit CIC bioGUNE Spain)
- Dr. Julian MOLOTKOVSKY (Shemyakin–Ovchinnikov Institute of Bioorganic Chemistry, RAS)
- Prof. Dinshaw PATEL (Structural Biology Program, Memorial Sloan–Kettering Cancer Center, USA)
- Prof. Rick E. BROWN (Hormel Institute, University of Minnesota, USA)
- Dr. Lucy MALININA (Structural Biology Unit CIC bioGUNE, Spain; Hormel Institute, University of Minnesota, USA)
- Dr. Borja OCHOA-LIZARRALDE (Structural Biology Unit CIC bioGUNE, Spain)
- Dr. Xouhong ZHAI (Hormel Institute, University of Minnesota, USA)
Protein-protein interactions are common in cell and molecular biology events, and essential for cellular function. Both homodimers and heterodimers are commonly involved in catalysis, regulation and structural assembly. However, the role of dimerization in controling the action of amphitropic peripheral proteins that can exist in water-soluble and lipid-bilayer-bound states is not well studied. Human Glycolipid Transfer Protein (GLTP) carries out the important function of non-vesicular transport of glycosphingolipids (GSLs) between membranes  but details of the all alpha-helical GLTP-fold mechanism of action remain unclear. Previously, reversible lipid-dependent dimerization was discovered for holo-GLTP . Structural studies using synchrotron radiation indicated a homodimer, reproducibly revealed in different crystal forms of GLTP bound with various GSLs. The homodimer is characterized by a 70-80 degree angle between wild-type monomers complexed with sulfatide, but the inter-monomer angle narrows to 63-66 degrees upon D48V mutation . The inter-monomer contacts were found to mainly involve helix6-helix6 (H6-H6), as well as helix2-helix2 (H2-H2) at their C-termini. The X-ray structure of another mutant, K87Q, complexed with 18:1-glucosyl¬ceramide, reveals a novel homodimer with a different dimerization contact region that includes the mutation site, which was not involved in the original dimerization contact region. Fluorescence spectroscopy assays involving intrinsic Trp emission changes show that K87Q-GLTP retains the original binding capacities for such GSLs, as sulfatide, glucosylceramide and galactosylceramide. Thus, GLTP dimer design could provide a way to dissect certain steps of the glycolipid transfer process. The influence of dimer type on steps of lipid transport by GLTP needs further investigation. This work was supported in part by Russian Foundation for Basic Research project 14-04-01671 and 15-04-07415, NIH NIGMS GM45928 and NCI121493, and CICbioGUNE research funds.
References: 1. Malinina L, Malakhova ML, Kanak AT, Lu M, Abagyan R, Brown RE, Patel DJ. The liganding mode of glycolipid transfer protein is controlled by glycosphingolipid structure. PLoS Biol. (2006). 4:e362. 2. Samygina VR, Ochoa-Lzarralde B, Popov AN, Cabo-Bilbao A, Goni-de-Cerio F, Molotkovsky JG, Patel DJ, Brown RE, Malinina L. Structural insights into lipid-dependent reversible dimerization of human GLTP. Acta Cryst. (2013). D69:603–616.