Structure
FSH is a glycoprotein. Each monomeric unit is a protein molecule with a sugar attached to it; two of these make the full, functional protein. Its structure is similar to those of LH, TSH, and hCG. The protein dimer contains 2 polypeptide units, labeled alpha and beta subunits. The alpha subunits of LH, FSH, TSH, and hCG are identical, and contain 92 amino acids. The beta subunits vary. FSH has a beta subunit of 111amino acids (FSH β), which confers its specific biologic action and is responsible for interaction with the FSH-receptor. The sugar part of the hormone is composed of fucose, galactose, mannose, galactosamine, glucosamine, and sialic acid, the latter being critical for its biologic half-life. The half-life of FSH is 3–4 hours.
The 92-amino-acid-long FSH alpha subunit in humans has the following sequence:
NH2 – Ala – Pro – Asp – Val – Gln – Asp – Cys – Pro – Glu – Cys – Thr – Leu – Gln – Glu – Asn – Pro – Phe – Phe – Ser – Gln – Pro – Gly – Ala – Pro – Ile – Leu – Gln – Cys – Met – Gly – Cys – Cys – Phe – Ser – Arg – Ala – Tyr – Pro – Thr – Pro – Leu – Arg – Ser† – Lys – Lys – Thr – Met – Leu – Val – Gln – Lys – Asn – Val – Thr – Ser – Glu – Ser – Thr – Cys – Cys – Val – Ala – Lys – Ser – Tyr – Asn – Arg – Val – Thr – Val – Met – Gly – Gly – Phe – Lys – Val – Glu – Asn – His – Thr – Ala – Cys – His – Cys – Ser – Thr – Cys – Tyr – Tyr – His – Lys – Ser – OH
- Note: The carbohydrate moiety is linked to the asparagine at positions 52 and 78.
The 111-amino-acid-long FSH beta subunit in humans has the following sequence:
NH2 – Asn – Ser – Cys – Glu – Leu – Thr – Asn – Ile – Thr – Ile – Ala – Ile – Glu – Lys – Glu – Glu – Cys – Arg – Phe – Cys – Ile – Ser – Ile – Asn – Thr – Thr – Trp – Cys – Ala – Gly – Tyr – Cys – Tyr – Thr – Arg – Asp – Leu – Val – Tyr – Lys – Asp – Pro – Ala – Arg – Pro – Lys – Ile – Gln – Lys – Thr – Cys – Thr – Phe – Lys – Glu – Leu – Val – Tyr – Glu – Thr – Val – Arg – Val – Pro – Gly – Cys – Ala – His – His – Ala – Asp – Ser – Leu – Tyr – Thr – Tyr – Pro – Val – Ala – Thr – Gln – Cys – His – Cys – Gly – Lys – Cys – Asp – Ser – Asp – Ser – Thr – Asp – Cys – Thr – Val – Arg – Gly – Leu – Gly – Pro – Ser – Tyr – Cys – Ser – Phe – Gly – Glu – Met – Lys – Glu – OH
- Note: The carbohydrate moiety is linked to the asparagine at positions 7 and 24.
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