PARNES, S*; RAVIV, S; ELDOR, R; SINGER, A; KEASAR, C; SAGI, A; Ben-Gurion University of the Negev, Israel: The vitellogenin of the penaeid shrimp Litopenaeus vannamei and a bioinformatic analysis of decapod vitellogenin deduced amino acid sequences

Vitellogenin (Vg) is the precursor for egg yolk protein, which stores most of the energy and building blocks for the future embryos in most oviparous organisms. In crustaceans it is synthesized mainly in the hepatopancreas and the ovary and transported to the oocyte through the hemolymph. In addition to L. vannamei Vg cDNA that was sequenced in our laboratory, there are now at least eight complete deduced amino acid (aa) sequences of decapod Vg available from the GenBank which are compared in this study. The ORF of decapod Vg is among the largest known (~8 kb), encoding an average of 2576�20 aa which is 4-6 times larger then the average eukaryote protein. The level of aa identities between L. vannamei Vg and other decapods is between 40 to nearly 90 %. Theoretical fragmentation of these Vg sequences yielded a long middle segment (approx. 1250 aa) that seems to have an evolution rate which is about 35% faster then its two flanking segments. The first of the latter segments contains a relatively well conserved Lipoprotein N-terminal Domain and an apolipoprotein region. The third segment contains a less conserved von Willebrand factor type D domain that still has to be assigned with a function. There is at least one conserved PC putative cleavage site consensus motif, which was indeed shown to be cleaved in several species. L. vannamei and other penaeid shrimps are outstanding in that they lack almost entirely N-linked glycosylation sites while crayfish, crab and caridean prawns have more then 10 such putative sites. An interesting outcome is that decapod Vg phylogenetic trees closely match other morphological and molecular trees, indicating the suitability of this protein for evolutionary studies.