Study summary · research use only
Crystal structure of a ternary complex between human chorionic gonadotropin (hCG) and two Fv fragments specific for the alpha and beta-subunits
Plain-language summary
Paraphrased from the published abstract below — not a verdict on whether anything works.
This structural study reports the crystal structure of a ternary complex of human chorionic gonadotropin (hCG), a human placental hormone, bound by two antibody Fv fragments, one specific for the alpha subunit and one for the beta subunit. The abstract states that hCG stimulates progesterone production and that its detection with monoclonal antibodies is used for pregnancy diagnosis. Crystals of the Fv anti-alpha/hCG/Fv anti-beta complex diffracted to 3.5 A resolution, and the structure was solved by molecular replacement. The authors describe the two Fv fragments holding hCG as in a molecular cage with space for the saccharides, contacting only the protein rather than the saccharides, and report that the hormone's structure was very close to that of a partially deglycosylated form.
Abstract
Human chorionic gonadotropin (hCG), is a placental hormone which exerts its major effect by stimulating progesterone production, crucially sustaining the early weeks of pregnancy. Detection of hCG with specific monoclonal antibodies (mAbs) has become the chosen means for pregnancy diagnosis. We have used antibody Fv fragments derived from two high-affinity mAbs, one against the alpha and the other against the beta-hCG subunit to enable the crystallisation of intact or desialylated hCG. Crystals of a ternary complex composed of Fv anti-alpha/hCG/Fv anti-beta were found to diffract to 3.5 A resolution, and the structure was solved by molecular replacement. In the crystal, the two Fvs keep hCG as in a molecular cage, providing good protein-protein contacts and leaving enough space for the saccharides to be accommodated in the cell solvent. The two Fvs were found not to interact directly through their complementary-determining regions with the hCG saccharides, but only with the protein. The hCG structure in the ternary complex was very close to that of the HF partially deglycosylated hormone, thus indicating that neither the saccharides nor the Fvs had any substantial influence on hormone structure.
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