Sandbox Reserved 1767: Difference between revisions
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== Introduction == | == Introduction == | ||
<scene name='95/952694/Overall_image/2'>The SHOC2-MRAS-PP1C</scene> (SMP) holophosphatase complex functions as a key regulator of the receptor tyrosine kinase (RTK) signaling pathway by removing an inhibitory phosphate on the RAF family of proteins to allow for MAPK signaling.<ref name="Kwon">PMID: 35831509</ref> This interaction of the RTK-Ras pathway and the SMP complex drives cell proliferation.<ref name="Hauseman">PMID:35830882</ref> The SMP complex is made of three subunits, SHOC2, PP1C, and MRAS. Each of these subunits has a different shape that corresponds to its different function. <scene name='95/952695/Shoc2intro/1'>The SHOC2 subunit</scene> uses a crescent shape to enhance substrate interactions and complex stability.<ref name="Liau">PMID: 35768504</ref> <scene name='95/952695/Pp1cintro/3'>The PP1C subunit</scene> contains the the catalytic site of the complex which dephosphorylates the N-terminal phosphoserine (NTpS) of RAF green link here.<ref name="Liau">PMID: 35768504</ref> <scene name='95/952694/Pp1ccorrectintro/1'>The MRAS subunit</scene> binds to GTP which triggers assembly of the SMP complex. The C-terminus of the MRAS subunit localizes the complex to the cell membrane.<ref name="Liau">PMID: 35768504</ref> | <scene name='95/952694/Overall_image/2'>The SHOC2-MRAS-PP1C</scene> (SMP) holophosphatase complex functions as a key regulator of the receptor tyrosine kinase (RTK) signaling pathway by removing an inhibitory phosphate on the RAF family of proteins to allow for MAPK signaling.<ref name="Kwon">PMID: 35831509</ref> This interaction of the RTK-Ras pathway and the SMP complex drives cell proliferation.<ref name="Hauseman">PMID:35830882</ref> The SMP complex is made of three subunits, SHOC2, PP1C, and MRAS. Each of these subunits has a different shape that corresponds to its different function. <scene name='95/952695/Shoc2intro/1'>The SHOC2 subunit</scene> uses a crescent shape to enhance substrate interactions and complex stability.<ref name="Liau">PMID: 35768504</ref> <scene name='95/952695/Pp1cintro/3'>The PP1C subunit</scene> contains the the catalytic site of the complex which dephosphorylates the N-terminal phosphoserine (NTpS) of RAF green link here.<ref name="Liau">PMID: 35768504</ref> <scene name='95/952694/Pp1ccorrectintro/1'>The MRAS subunit</scene> binds to GTP which triggers assembly of the SMP complex. The C-terminus of the MRAS subunit localizes the complex to the cell membrane.<ref name="Liau">PMID: 35768504</ref> Once the SMP compelx is assembled, MRAS can bind to <scene name='95/952695/Raf/2'>RAF</scene>, allowing the signaling cascade to continue. Mutations in one or multiple of these subunits leads to over-activation of the signaling pathway, which may result in cancer and developmental disorders called RASopathies.<ref name="Kwon">PMID: 35831509</ref> | ||
There are many regulatory mechanisms that serve as a lock on this RAS-MAPK pathway, decreasing the likelihood of unintentional pathway activation. One is a protein dimer called 14-3-3 that keeps inactive RAF localized to the cytoplasm. An N-terminal phosphorylated serine (NTpS) keeps RAF bound to this protein dimer, and when the SMP complex is assembled, the catalytic subunit, PP1C, removes the phosphate group from the serine residue, releasing RAF from the 14-3-3 dimer, and activating the RAS-MAPK cell proliferation pathway. | There are many regulatory mechanisms that serve as a lock on this RAS-MAPK pathway, decreasing the likelihood of unintentional pathway activation. One is a protein dimer called 14-3-3 that keeps inactive RAF localized to the cytoplasm. An N-terminal phosphorylated serine (NTpS) keeps RAF bound to this protein dimer, and when the SMP complex is assembled, the catalytic subunit, PP1C, removes the phosphate group from the serine residue, releasing RAF from the 14-3-3 dimer, and activating the RAS-MAPK cell proliferation pathway. | ||
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The presence of <scene name='95/952695/Shoc2intro/1'>SHOC2</scene> is essential for complex formation. It a crescent shaped complex that serves as a bridge for PP1C and MRAS, maximizing interaction between the three subunits of the SMP complex. SHOC2 contains a large leucine rich region (LRR) that provides stability and localizes subunit PP1C to the membrane<ref name="Liau">PMID: 35768504</ref>. SHOC2 only undergoes a <scene name='95/952693/Shoc2_gtp_bound_vs_gdp_bound/7'>6° conformational change</scene> when PP1C and MRAS bind, showing SHOC2 is a scaffolding protein that provides a favorable interface for complex formation<ref name="Liau">PMID: 35768504</ref>. SHOC2 depletion is being studied as a therapeutic approach for RAS-driven cancers due to large scale interactions of the subunits being made possible by SHOC2. <ref name="Kwon">PMID: 35831509</ref>. SHOC2 and PP1C first engage in binding with each other via an N-terminal RVXF motif on SHOC2 that is complimentary to a sequence on PP1C. SHOC2 residues V64 and F66 '''GREEN LINK?''' embed in the complimentary region of PP1C, enhancing SHOC2 affinity for PP1C. SHOC2 bind MRAS-GTP through β strands of a LRR that interacts with a hydrophobic region of MRAS-GTP further stabilizing the complex. KWON | The presence of <scene name='95/952695/Shoc2intro/1'>SHOC2</scene> is essential for complex formation. It a crescent shaped complex that serves as a bridge for PP1C and MRAS, maximizing interaction between the three subunits of the SMP complex. SHOC2 contains a large leucine rich region (LRR) that provides stability and localizes subunit PP1C to the membrane<ref name="Liau">PMID: 35768504</ref>. SHOC2 only undergoes a <scene name='95/952693/Shoc2_gtp_bound_vs_gdp_bound/7'>6° conformational change</scene> when PP1C and MRAS bind, showing SHOC2 is a scaffolding protein that provides a favorable interface for complex formation<ref name="Liau">PMID: 35768504</ref>. SHOC2 depletion is being studied as a therapeutic approach for RAS-driven cancers due to large scale interactions of the subunits being made possible by SHOC2. <ref name="Kwon">PMID: 35831509</ref>. SHOC2 and PP1C first engage in binding with each other via an N-terminal RVXF motif on SHOC2 that is complimentary to a sequence on PP1C. SHOC2 residues V64 and F66 '''GREEN LINK?''' embed in the complimentary region of PP1C, enhancing SHOC2 affinity for PP1C. SHOC2 bind MRAS-GTP through β strands of a LRR that interacts with a hydrophobic region of MRAS-GTP further stabilizing the complex. KWON | ||
=== PP1C === | === PP1C === | ||
The Protein | <scene name='95/952695/Pp1cintro/3'>The Protein Phosphatase Complex 1 (PP1C)</scene> subunit contains the catalytic site of the SMP complex. The PP1C subunit is a phosphatase enzyme responsible for the removal of a phosphate group on the N-terminal phosphoserine (NTpS) of RAF (Ser259).<ref name="Liau">PMID: 35768504</ref>. The exact mechanism of dephosphorylation is currently unknown, but there are three catalytic metal ions: 2 Mn2+ and 1 Cl- present that coordinate nucleophilic water molecules in the active site. This dephosphorylation event allows for pathway activation. Although PP1C can dephosphorylate other proteins independently from the SMP complex, it cannot act on Raf unless bound to the complex because it lacks intrinsic substrate selectivity.<ref name="Liau">PMID: 35768504</ref> SHOC2 and MRAS aid in the specificity of the enzymatic activity. Hence, PP1C requires the presence of SHOC2 and MRAS to be function. <ref name="Hauseman">PMID:35830882</ref> PP1C binds to SHOC2 and MRAS-GTP in a specific orientation that doesn’t change the conformation of the catalytic site and leaves it accessible for substrate binding. | ||
PP1C binds to SHOC2 through a hydrophobic n-terminal disordered region that is complimentary to the RVXF motif on SHOC2. GREEN LINK or picture? Similarly to SHOC2, PP1C does not undergo a significant conformational change when SHOC2 and MRAS-GTP bind. The lack of conformational change shows that the structure of PP1C is not dependent on the SMP complex, but in order to act as a phosphatase it must be bound to the complex.<ref name="Liau">PMID: 35768504</ref>. | PP1C binds to SHOC2 through a hydrophobic n-terminal disordered region that is complimentary to the RVXF motif on SHOC2. GREEN LINK or picture? Similarly to SHOC2, PP1C does not undergo a significant conformational change when SHOC2 and MRAS-GTP bind. The lack of conformational change shows that the structure of PP1C is not dependent on the SMP complex, but in order to act as a phosphatase it must be bound to the complex.<ref name="Liau">PMID: 35768504</ref>. | ||
PP1C binds to SHOC2 and MRAS-GTP in a specific orientation that does not cause a change in the conformation of the catalytic site and leaves it accessible for substrate binding. '''GREEN LINK or picture?''' | PP1C binds to SHOC2 and MRAS-GTP in a specific orientation that does not cause a change in the conformation of the catalytic site and leaves it accessible for substrate binding. '''GREEN LINK or picture?''' | ||
