Sandbox Reserved 1661: Difference between revisions
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Somatotropin does not exist as a linear chain of amino acids, it twists and folds on itself, forming the '''secondary structure'''. The protein, made up of a single chain, consists of four antiparallel aligned <scene name='86/868194/Halpha/1'>α-helices</scene> in an up-up-down-down manner <ref name="Endokrynologika Polska">DOI:10.5603/EP.2013.0009</ref>. The first helix starts at the 6th amino acid, which is a leucine and ends with the 37th amino acid proline. It is separated from the other three helices after the 37th position. The 38th and 39th amino acids, which are lysine and glutamic acid are spliced out of the protein and therefore disconnects the first helix from the second one. The second helix starts at position 72 till 92, the third from 106 till 128 and the fourth helix from 155 until 184. All helices are ampipathic with strong hydrophobic regions, especially helix 2 is very hydrophobic. The hydrophobic protein core is usually tigthly packed and any mutations in the hidden positions lead to destablilization <ref name="pubMed">PMID:17584122</ref>. | Somatotropin does not exist as a linear chain of amino acids, it twists and folds on itself, forming the '''secondary structure'''. The protein, made up of a single chain, consists of four antiparallel aligned <scene name='86/868194/Halpha/1'>α-helices</scene> in an up-up-down-down manner <ref name="Endokrynologika Polska">DOI:10.5603/EP.2013.0009</ref>. The first helix starts at the 6th amino acid, which is a leucine and ends with the 37th amino acid proline. It is separated from the other three helices after the 37th position. The 38th and 39th amino acids, which are lysine and glutamic acid are spliced out of the protein and therefore disconnects the first helix from the second one. The second helix starts at position 72 till 92, the third from 106 till 128 and the fourth helix from 155 until 184. All helices are ampipathic with strong hydrophobic regions, especially helix 2 is very hydrophobic. The hydrophobic protein core is usually tigthly packed and any mutations in the hidden positions lead to destablilization <ref name="pubMed">PMID:17584122</ref>. | ||
From the secondary structure, we obtain the '''tertiary structure''', which corresponds to the 3D structure adopted by all the alpha helixes. The structural maintenance is stabilised by electrostatic, hydrophobic and polar interactions, <scene name='86/868194/Lh/1'>hydrogen bonds</scene> and/or covalent interactions with cysteine 53 and cysteine 165 that form a <scene name='86/868194/Pds/2'>disulphide bridge</scene> as well as cysteine 182 with cysteine 189. Cys53 and C165 also link the crossover connection between helices 1 and 2 to helix 4. The other cysteine-pair form a small loop in C-terminus, involved in the receptor binding site 1. <ref name="Endokrynologika Polska">DOI:10.5603/EP.2013.0009</ref> | From the secondary structure, we obtain the '''tertiary structure''', which corresponds to the 3D structure adopted by all the alpha helixes. The structural maintenance is stabilised by electrostatic, hydrophobic and polar interactions, <scene name='86/868194/Lh/1'>hydrogen bonds</scene> and/or covalent interactions with cysteine 53 and cysteine 165 that form a <scene name='86/868194/Pds/2'>disulphide bridge</scene> as well as cysteine 182 with cysteine 189. Cys53 and C165 also link the crossover connection between helices 1 and 2 to helix 4. The other cysteine-pair form a small loop in C-terminus, involved in the receptor binding site 1. It is also requiried for stability, but unlike the first cysteine-pair not essential for biological activity <ref name="Endokrynologika Polska">DOI:10.5603/EP.2013.0009</ref>. | ||
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 GH consists of two hydrophobic cores, one is composed of Trp104 (hGH-receptor1), Trp169(hGH-receptor1), Pro61 (hGH), Phe176(hGH) and Ile176(hGH). Especially Pro61 is important, it is involved in the formation of the ative conformation of hydrophobic core amino acids and interacting with other hydrophobic core amino acids within 5Å. A mutation in this point leads to a decrease of biological and receptor binding activity. The other one is composed of two pairs of interaction between Trp76 (hGH-receptor1) and Pro48 (hGH) and between Pro106 (hGH-receptor1) and Leu45 (hGH). <ref name="pubMed">PMID:17584122</ref> | The GH consists of two hydrophobic cores, one is composed of Trp104 (hGH-receptor1), Trp169(hGH-receptor1), Pro61 (hGH), Phe176(hGH) and Ile176(hGH). Especially Pro61 is important, it is involved in the formation of the ative conformation of hydrophobic core amino acids and interacting with other hydrophobic core amino acids within 5Å. A mutation in this point leads to a decrease of biological and receptor binding activity. The other one is composed of two pairs of interaction between Trp76 (hGH-receptor1) and Pro48 (hGH) and between Pro106 (hGH-receptor1) and Leu45 (hGH). <ref name="pubMed">PMID:17584122</ref> | ||
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 lacks amino acids 32 to 71 and causes isolated GH deficiency type II. The entire connecting loop between helices 1 and 2 and the Cys53 which is required for the first disulphide bridge is missing which leads to unpaired cysteine. 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> <ref name="Endokrynologika Polska">DOI:10.5603/EP.2013.0009</ref> | |||
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 | |||
</StructureSection> | </StructureSection> | ||
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The HGH receptor is a transmembrane protein consisting of 620 amino acids. It has two extracellular domains, highly conserved, each containing 7 β-sheets. The protein should theoretically have a molecular mass of 70 kDa considering the amino acid sequence. In fact the actual molecular weight is 100 - 130 kDa. This can be explained due to post-translational modifications such as glycosylation and ubiquitination. Ligand binding increases ubiquitination and possibly has effect on GH receptor internalisation. | The HGH receptor is a transmembrane protein consisting of 620 amino acids. It has two extracellular domains, highly conserved, each containing 7 β-sheets. The protein should theoretically have a molecular mass of 70 kDa considering the amino acid sequence. In fact the actual molecular weight is 100 - 130 kDa. This can be explained due to post-translational modifications such as glycosylation and ubiquitination. Ligand binding increases ubiquitination and possibly has effect on GH receptor internalisation. | ||
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 two binding sites are allosterically coupled, this effect focused among some residues centered around the interaction between Asp116 (hGH) and Trp169 (hGH-receptor2). <ref name="pubMed">PMID:17584122</ref> | 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> <ref name="Endokrynologika Polska">DOI:10.5603/EP.2013.0009</ref>. This leads to receptor homodimerization and transmits the signal into the target cell. The two binding sites are allosterically coupled, this effect focused among some residues centered around the interaction between Asp116 (hGH) and Trp169 (hGH-receptor2). <ref name="pubMed">PMID:17584122</ref> | ||
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> | 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> | ||
