Lipid-binding proteins types

Of all the novel protein types found in nematodes, only two have had biochemical activites ascribed, and these both happen to be lipid-binding proteins (LBPs). This chapter will focus on these, plus those that are structurally similar to those of vertebrates but appear to have nematode-specific modifications to their structures and functions. 

The various types of novel lipid-binding protein from nematodes can... 

There are many more ways to build a lipid transport protein for small lipids than previously known. The NPAs, for instance, have similar ligand-binding propensities to similarly sized LBPs of vertebrates, but are helix-rich rather than being P-rich. The LBP-20-type proteins represent yet another novel type of LBP. 

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... 

The association of lipids with proteins in dilute aqueous solutions was studied by Tanford (15). He identified different types of interaction that depend on the number of associated lipid molecules. He also analyzed the relation between lipid association into micelles and the competing binding of lipids to proteins. 

The FABPs are a family of carrier proteins for fatty acids and other lipophilic substances, such as eicosanoids and retinoids. These proteins are thought to facilitate the transfer of fatty acids between extra- and intracellular membranes. Adipocyte fatty acid-binding protein (aP2 FABP4) is expressed in adipocytes and macrophages, and integrates inflammatory and metabolic responses. Studies in aP2-deflcient mice have shown that this lipid chaperone has a significant role in several aspects of the metabolic syndrome, including type 2 diabetes and atherosclerosis. FABP has also been introduced as a plasma marker of acute myocardial infarction. 

In schematic diagrams, P strands are usually depicted by broad arrows pointing in the direction of the carboxyl-terminal end to indicate the type of P sheet formed—parallel or antiparallel. More structurally diverse than a helices, P sheets can be relatively flat but most adopt a somewhat twisted shape (Figure 3.40). The P sheet is an important structural element in many proteins. For example, fatty acid-binding proteins, important for lipid metabolism, are built almost entirely from P sheets (Figure 3.41). 

The lipids of the diet include TGs, phospholipids, cholesteryl esters, cholesterol, and the fat-scivble vitamins. These nutrients require special types of biochemical machinery to facilitate their assimilation and distributicrt within the body. The biochemical apparatus used includes bile salts, apolipoprotcins, serum albumin, and vitamin-binding proteins. Apolipopnoteins are the primary subject of this section. The term apolipoprotain is used when referrmg only to the protein, whereas the term lipoprotein refers to the complex of apolipoprotein and lipid. 

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