Identification of Naturally Occurring Follistatin Complexes: DISCUSSION(3)

This seems plausible for FS because of structural aspects of the protein: the presence of numerous cysteines that could form cysteine knots; the presence of splice variants, FS288 or FS315, differing by a 27-amino acid sequence that is 44% acidic in humans; and the ability to bind to proteoglycans, which may allow FS to be membrane bound. The different FS iso-forms—F2288,FS303 (byprotoolyticcleavafe)aOnd FS315—may infunsiionalcapauity. Ithabbeen suggested that the presence of the 27-emino acid tail appears to mask a heparan sulfate proteoglycan-binding site, such that the three different isoforms have different affinities to a cell surface (i.e., the surface of a granulosa cell). FS288 binds with greatest affinity (ED50 = 2 ng/ml), while FS303 has less affinity (ED50 = 10 ng/ml) and FS315 does not associate. ampicillin antibiotic

Another consideration regarding the difficulty in reducing FS may be that the reduced FS has a less negative charge because its structure or hydration shell does not allow for accessibility to a reductant, thus resulting in a larger protein size upon reduction. Although the activin-binding activity is fairly similar for the three isoforms (Kd = 540-680 pM), it is possible that the difference in the isoform size or in cellular binding ability could alter FS interactions with inhibin.

This entry was posted in Biological Fluids and tagged Biological Fluids, Follistatin Complexes, Human.