The vitellogenin (VTG) protein, a major lipoprotein in many oviparous animals, is a precursor of a lipid-binding product named as lipovitellin. Lipovitellin is the major lipid-protein complex found in the yolk of egg-laying animals, and is involved in lipid and metal storage. At the N-terminal, it contains a sequence of about 670 amino acids (LV1n chain), which is also conserved in other large lipoproteins, such as microsomal triglyceride transfer protein (MTP) and apolipoprotein B-100 (apoB) [1,2,3].

The crystal structure of lipovitellin has been solved (see <PDB:1LSH>) [4]. It shows that the N-terminal domain (LV1n chain) contains two subdomains the N sheet, and the helical subdomain. It also includes portions of two more subdomains, which are part of the LV1c chain, one β-strand of the A-sheet, and five β-strands of the C-sheet. The N-sheet subdomain forms a barrel-like conformation. It contains two disulfide bridges (cys1-cys2, cys3-cys4). The first disulfide bridge appears to be conserved in both MTP and apoB [1,4]. The helical subdomain has a crescent shape. This subdomain also contains one disulfide bridge (cys1-cys2) [1,3]. The lipid-binding cavity is formed primarily by the A and C sheets and a small section of the helical domain. It is roughly funnel- or cup-shaped. The phosphatidylcholine, L1, binds in a large loop at the narrow end of the lipid 'funnel'. This loop region is stabilized on both ends by the N-sheet disulfide bridges. L2 is located in a nonpolar region of the protein and has hydrophobic interactions with residues from the N sheet. The other part of the binding site derives from the A sheet and includes side chains from the LV1c.

Some proteins known to contain a vitellogenin domain are listed below:

• Insect apolipophorin II/I precursor (apoLp-II/I), which mediates transport for various types of lipids in hemolymph. It acts by forming lipoprotein particles that bind lipoproteins and lipids.
• Human apolipoprotein B (apoB), which is a major protein constituent of chylomicrons (apo B-48), LDL (apo B-100) and VLDL (apo B-100). Apo B-100 functions as a recognition signal for the cellular binding and internalization of LDL particles by the apoB/E receptor
• Invertebrate and vertebrate vitellogenins (VTG), which is precursor of the egg-yolk proteins that are sources of nutrients during during early development of oviparous organisms.
• The large subunit of mammalian microsomal triglyceride transfer protein (MTP), which catalyzes the transport of triglyceride, cholesteryl ester, and phospholipid between phospholipid surfaces. It is required for the secretion of plasma lipoproteins that contain apolipoprotein B.

We developed a profile for this domain, that spans the whole LV1n domain.