Lipid-binding proteins difference

In summary, the overall structures of the LBPs have a motif common to a variety of other proteins. Different forms of the /8 barrel have been observed in other lipid-binding proteins as well as in other globular proteins. The unique feature of the LBPs should be visible in Fig. 2. The distinctive feature of the LBPs is their /8-barrel architecture that gives rise to a cavity accommodating a hydrophobic ligand. 

Although the insect lipid-binding protein has the same structural motif as other iLBPs, the side chains used to define the specificity site are somewhat different and appear to include an additional anion (Benning et al., 1992). In addition, the ligand has a different conformation and the overall structure suggests that a different portal might be favored in this protein. 

In addition, the carboxylate group of bound fatty acid was in a solvent-accessible environment, suggesting a lipid-binding mode different from that of wild-type protein. Furthermore, this mutant had an affinity for retinol when the wild-type IFABP had none (Jakoby el al, 1993). These experiments show that it is possible to switch the binding specificity of iLBP proteins by mutating individual amino acids associated with the specificity motif. These results do not, however, indicate that the mutated positions are singularly responsible for ligand selectivity. Substitution of other cavity residues may have similar or contributory effects. 

Lerche, M.H. and Poulsen, F.M. (1998) Solution structure of barley lipid transfer protein complexed with palmitate. Two different binding modes of palmitate in the homologous maize and barley nonspecific lipid transfer proteins. Protein Science 7, 2490-2498. 

To demonstrate an application of TIRF-FLIM, a FRET study of annexin A4 translocation and self-aggregation near the plasma membrane is shown in Fig. 9.4. This is a particularly useful application of TIRF-FLIM, since TIRF provides the spatial contrast of detecting only molecules immediately adjacent to the plasma membrane and the lifetime contrast reports on the aggregation state of annexin A4. Annexins are calcium-dependent lipid-binding domains with a different type of lipid binding domain compared to the common C2 domains (e.g., found in protein kinase C). Annex-ins consist of an N-terminal domain and a core domain binding calcium and phospholipids. The core domain is conserved in the... 

Lins et al. 127 have studied five peptide sequences derived from the ApoB-100 protein, which is the protein moiety in low-density lipoproteins (LDC) that transport cholesterol. ApoB-100 is insoluble and binds to the surface of the LDC particle, and these selected sequences for this study have been implicated as being important in the lipid binding. ATR-FTIR studies showed the one core and three C-terminal originating sequences were mostly sheet-like in the presence of unilamellar vesicles but the N-terminal one was different, probably representing a complex mixture of conformers with some helical component. Furthermore, these workers were able to carry out ATR-LD measurements and determine the orientation of the peptide as being oblique to the membrane. These studies are in contrast to ultraviolet ECD results which were adversely affected by scattering artifacts. 

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