The latest amazingly framework including indicated that the new FSH/FSHR advanced forms good dimer making use of the outer surface away from LRRs 2-cuatro regarding hFSHR. cuatro ) failed to affect the dimerization of the hFSHR expressed inside the heterologous mobile sizes, yet not. 217 The fresh amazingly design of your own TSHR within the complex which have a TSHR antibody don’t show any dimers. 216
Because depend region was lost about a couple of ECD amazingly structures, there’s nothing understood about the contribution with the total conformation away from this new ECD and/or receptors. This new discovering that residues step 1-268 of one’s hFSHR (the new fragment useful for the fresh new crystal structure) binds hFSH with a high affinity means that the fresh new depend region of the fresh hFSHR isn’t involved in binding. On top of that, a great amount of lab-tailored and of course-taking place mutations of LHR reveal that the latest count area for new hLHR isn’t important for new higher-attraction joining out-of hLH otherwise hCG. 211 Nonetheless, the new highest level of conservation of some count part deposits for the the glycoprotein hormone receptor relatives ( Fig. dos.4 ) suggests that this region takes on a crucial role in other points out-of receptor means particularly activation (handled later about text message). An extremely spared Tyr present in this place ( Fig. dos.4 ) are shown to be sulfated on the phone surface TSHR and you can mutation of this Tyr impairs TSH binding and you may activation. 218 Sulfation of your similar Tyr throughout the LHR or FSHR has not been shown, but mutations regarding the deposit from the gonadotropin receptors together with impact hormones binding and you can activation. ? 218
The serpentine domain of the gonadotropin receptors is characterized by the canonical GPCR structure containing seven transmembrane (TM) segments joined by three alternating intracellular and extracellular loops ( Fig. 2.4 ). The amino acid sequences of this region of the hLHR and hFSHR are 72% identical ( Fig. 2.4 ). A three dimensional structure of the transmembrane domain of the gonadotropin receptors is lacking but the three dimensional structure of several other GPCRs with short extracellular domains have now been solved 213 (also see ) and the transmembrane domain of the gonadotropin receptors is likely to be very similar. Transmembrane domain residues that are highly conserved among the rodhopsin/?2-adrenergic receptor-like subfamily of GPCRs are also highlighted in Figure 2.4 .
27% identity, Fig. 2.4 ). An intracellular cysteine residue present in the juxtamembrane region of the C-terminal tail of the rodhopsin/?2-adrenergic receptor-like subfamily of GPCRs is, however, among the most highly conserved residues of this subfamily of GPCRs and all members of this subfamily examined to date have been shown to be palmitoylated at this site. This cysteine is towards the C-terminal end of a cytoplasmic helical segment of other GPCRs that is referred to as helix 8 ( ) and the palmitate present at this highly conserved position is thought to be embedded in the membrane. The LHR is unusual in having two adjacent cysteines in this position ( Fig. 2.4 ). Although the palmitoylation of the hLHR has not been studied, the mature form of the rLHR expressed in 293 cells, has been shown to be palmitoylated at both of these residues. 211 The equivalent cysteine in the hFSHR is also palmitoylated. 219
New hinge part
A separately encoded ‘hinge’ region is inserted between the CH1 and CH 2 domains. Portions of the hinge regions of two human IgG1 antibodies can be seen in Figure 3 and 4 . In the human and murine IgG1 subclasses, the initial part of the hinge region supplies the half-cysteine residue which forms the interchain disulfide bond with the L chain (see Figure 4 ). Its half-cystine counterpart in the L chain occupies the C-terminal location in a ? chain and the penultimate position in a ? chain. Disulfide bonds linking the two heavy chains are found in a relatively rigid ‘core’ segment (Cys-Pro-Pro-Cys-Pro) of the hinge region. Segments flanking this core section are responsible for the flexibility suggested by the name ‘hinge’. Papain hydrolyzes peptide bonds among residues 6–10 of the upper flexible segment (‘proximal hinge’) between the H–H and the H–L interchain disulfide bonds to produce Fabs. Pepsin cleaves the lower flexible segment (‘distal hinge’) after the disulfide bonds to release a (Fab?)2 fragment.