ISOLATION AND IDENTIFICATION OF PORCINE EMBRYONIC BASIC-PROTEIN AS A FRAGMENT OF PREGNANCY-ASSOCIATED GLYCOPROTEIN-2

Between days 11 and 12 of gestation, the porcine conceptus undergoes a metamorphosis from a spherical blastocyst to an elongate thread-like form, During this process, the conceptus secretes a variety elf produc ts. One of these products is a protein previously referred to as porci ne embryonic basic protein (BP). This protein has been shown to be a m ajor secreted product between days 13 and 18, In this study, we report a simple two-step procedure to isolate BP from day 15 porcine concept us conditioned medium, utilizing ion-exchange chromatography and rever se-phase HPLC, Purified BP was subjected to Edman degradation amino-te rminal sequencing and a 25 amino acid residue sequence was obtained. C omparing the N-terminal sequence of BP to sequences ill the GenBank da tabase determined that BP shared amino acid homology with porcine preg nancy-associated glycoprotein-2 (PAG-2). The region of identity corres ponded to an internal site of PAG-2, suggesting BP was a proteolytic f ragment of PAG-2. The purified protein was confirmed to be BP by Weste rn blot using a previously characterized anti-BP antiserum, Also, the BP was immunolocalized within the trophectoderm of day 11 blastocysts, Staining intensity was diminished in spherical blastocysts compared t o elongated blastocysts. Although the function of PAG-2 rind its cleav age product BP are unknown, the large quantity produced by the porcine conceptus and its sequence conservation across species may indicate a necessary role in early pregnancy. Copyright (C) 1996 Published by El sevier Science Ltd