Sandbox Reserved 1661: Difference between revisions
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The protein has two different binding sites: both located at the ends of the protein, the N-terminus as well as the C-terminus. | The protein has two different binding sites: both located at the ends of the protein, the N-terminus as well as the C-terminus. | ||
The second isoform was found in blood circulation and lost the amino acids 32 till 46 due to alternative splicing of the pre-mRNA and therefore has a molecular weight of 20 kDa. It has a reduced insulin linked activity but is still very similiar to the predominant form, although a quarter of the amino acids in the long loop between helices 1 and 2 was deleted. The loss of these amino acids could be compensated due to the flexibility of the loop region. Through the lack of Lys41, the isoform can not form a saltbridge between hGH and the first receptor. It is possible for the hGH to compensate partially a deficit of 200Å contact surface area through Pro33 and Leu37 in hydrophobic interaction and Arg152 in salt bridge. The third isoform has a molecular weight of 17,5kDa and is formed by alternative splicing of the pre-mRNA. A mutation in the first and sixth basepair leads to a missplicing of the mRNA and loss of exon 3. The GH produced thus lacks amino acids 32 to 71. The entire connecting loop between helices 1 and 2 and the Cys53 which is required for the first disulphide bridge is missing. Some deleted amino acids are part of a hydrophobic core which is essential to fold the molecule normally. The molecule gets instabil, it can not refold properly. | The second isoform was found in blood circulation and lost the amino acids 32 till 46 due to alternative splicing of the pre-mRNA and therefore has a molecular weight of 20 kDa. It has a reduced insulin linked activity but is still very similiar to the predominant form, although a quarter of the amino acids in the long loop between helices 1 and 2 was deleted. The loss of these amino acids could be compensated due to the flexibility of the loop region. Through the lack of Lys41, the isoform can not form a saltbridge between hGH and the first receptor. It is possible for the hGH to compensate partially a deficit of 200Å contact surface area through Pro33 and Leu37 in hydrophobic interaction and Arg152 in salt bridge. The third isoform has a molecular weight of 17,5kDa and is formed by alternative splicing of the pre-mRNA. A mutation in the first and sixth basepair leads to a missplicing of the mRNA and loss of exon 3. The GH produced thus lacks amino acids 32 to 71. The entire connecting loop between helices 1 and 2 and the Cys53 which is required for the first disulphide bridge is missing. Some deleted amino acids are part of a hydrophobic core which is essential to fold the molecule normally. The molecule gets instabil, it can not refold properly. Additionally, the receptor can not bind to binding site 1 which leads to a huge loss in activity. <ref name="pubMed">PMID:17584122</ref> | ||
A large number of reports are published on structre-function relationship of GH using chemical modifications, proteolytic digestion or molecular biological methods to alter or delete amino acids or regions. Mutations in the structure lead often to alterations of the binding characteristics due to the effects on protein confirmation. | A large number of reports are published on structre-function relationship of GH using chemical modifications, proteolytic digestion or molecular biological methods to alter or delete amino acids or regions. Mutations in the structure lead often to alterations of the binding characteristics due to the effects on protein confirmation. | ||
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Binding to the receptor is the first step in the biological action of the hormone.<ref name="m/s"/> For the binding of a single HGH, two HGH receptors are needed. The HGH binds with its high affinity binding site 1 onto the extracellular domain of the first receptor and with the low affinity binding site 2 onto the extracellular domain of the second receptor <ref name="pubMed">PMID:17584122</ref>. This leads to receptor homodimerization and transmits the signal into the target cell. | Binding to the receptor is the first step in the biological action of the hormone.<ref name="m/s"/> For the binding of a single HGH, two HGH receptors are needed. The HGH binds with its high affinity binding site 1 onto the extracellular domain of the first receptor and with the low affinity binding site 2 onto the extracellular domain of the second receptor <ref name="pubMed">PMID:17584122</ref>. This leads to receptor homodimerization and transmits the signal into the target cell. | ||
The first binding site of the HGH protein contains parts of helices 1 and 4, as well as parts of the binding loop between helices 1 and 2. The second binding site contains the N-terminus and part of the third helix. Major roles hereby play Phenylalanine 1 and Isoleucine 4 (N-terminus) and Aspartic acid 116. The C-terminal part of the receptor, consisting of the last 165 amino acids, has no effect on GH binding.<ref name="m/s"/> | The first binding site of the HGH protein contains parts of helices 1 and 4 (amino acids 103-119), as well as parts of the binding loop between helices 1 and 2 (amino acids 41-68). The second binding site contains the N-terminus and part of the third helix (amino acids 54-74). Major roles hereby play Phenylalanine 1 and Isoleucine 4 (N-terminus) and Aspartic acid 116. The C-terminal part of the receptor, consisting of the last 165 amino acids, has no effect on GH binding.<ref name="m/s"/> <ref name="pubMed">PMID:17584122</ref> | ||
Several GH variants with modified N-terminus were explored to learn more about the behaviour of the binding of the receptor molecule. A GH with an extension of Methionin on the N-terminus behave identical to an authentic GH in assays. The small, neutral amino acid without any side chains has no apparent effect on the binding of the receptor. In contrast, a removal of 13 amino acids at the N-terminus results in reduced binding activity to somatogenic receptors and decreased biological activity, because the amino acids 1 to 16 are involved in the binding site 2. But the other part of the binding site (with Trp103, Asp116 and Glu119 from helix 3) of the hGH molecule are intact and available for binding of the receptor. The N-terminus is required for full biological activity, however, additions still deletions can not completly abolish the functions of the molecule. <ref name="pubMed">PMID:17584122</ref> | Several GH variants with modified N-terminus were explored to learn more about the behaviour of the binding of the receptor molecule. A GH with an extension of Methionin on the N-terminus behave identical to an authentic GH in assays. The small, neutral amino acid without any side chains has no apparent effect on the binding of the receptor. In contrast, a removal of 13 amino acids at the N-terminus results in reduced binding activity to somatogenic receptors and decreased biological activity, because the amino acids 1 to 16 are involved in the binding site 2. But the other part of the binding site (with Trp103, Asp116 and Glu119 from helix 3) of the hGH molecule are intact and available for binding of the receptor. The N-terminus is required for full biological activity, however, additions still deletions can not completly abolish the functions of the molecule. <ref name="pubMed">PMID:17584122</ref> | ||
