Sandbox Reserved 1767: Difference between revisions
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<scene name='95/952695/Shoc2intro/1'>SHOC2</scene> is essential for complex formation. It is a crescent shaped complex that serves as a bridge for PP1C and MRAS, maximizing interaction between the three subunits of the SMP complex <ref name="Hauseman">PMID:35830882</ref>. 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 it 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>. As shown in '''Figure 1 '''SHOC2 and PP1C first engage in binding with each other via an N-terminal <scene name='95/952695/Rvxf_motif/2'>RVXF Motif</scene> on SHOC2 that is complimentary to a binding sequence on PP1C. SHOC2 residues <scene name='95/952695/Shoc2_highlighted_residues/1'>V64 and F66</scene> embed in the complimentary region of PP1C, enhancing SHOC2 affinity for PP1C. SHOC2 binds MRAS-GTP through β strands of a LRR that interacts with a [https://pubmed.ncbi.nlm.nih.gov/21954777/. hydrophobic] region of MRAS-GTP further stabilizing the complex<ref name="Kwon">PMID: 35831509</ref>. | <scene name='95/952695/Shoc2intro/1'>SHOC2</scene> is essential for complex formation. It is a crescent shaped complex that serves as a bridge for PP1C and MRAS, maximizing interaction between the three subunits of the SMP complex <ref name="Hauseman">PMID:35830882</ref>. 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 it 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>. As shown in '''Figure 1 '''SHOC2 and PP1C first engage in binding with each other via an N-terminal <scene name='95/952695/Rvxf_motif/2'>RVXF Motif</scene> on SHOC2 that is complimentary to a binding sequence on PP1C. SHOC2 residues <scene name='95/952695/Shoc2_highlighted_residues/1'>V64 and F66</scene> embed in the complimentary region of PP1C, enhancing SHOC2 affinity for PP1C. SHOC2 binds MRAS-GTP through β strands of a LRR that interacts with a [https://pubmed.ncbi.nlm.nih.gov/21954777/. hydrophobic] region of MRAS-GTP further stabilizing the complex<ref name="Kwon">PMID: 35831509</ref>. | ||
=== PP1C === | === PP1C === | ||
[[Image:CS.png|300 px|right|thumb|'''Figure 2:''' Catalytic Site of PP1C (PDB 7DSO) <ref name="Liau">PMID: 35768504</ref>.]] | [[Image:CS.png|300 px|right|thumb|'''Figure 2:''' Catalytic Site of PP1C (PDB 7DSO). The catalytic site is shown in red. PP1C undergoes minimal conformational change when binding to SHOC2 and MRAS to ensure the active site is available for binding of RAF. <ref name="Liau">PMID: 35768504</ref>.]] | ||
<scene name='95/952695/Pp1cintro/3'>The Protein Phosphatase Complex 1 (PP1C)</scene> subunit contains the catalytic site of the SMP complex. PP1C is a [https://pubmed.ncbi.nlm.nih.gov/30036567/. 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 Mn⁺² and 1 Cl⁻¹ present that coordinate [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3458771/. nucleophilic] water molecules in the active site <ref name="Hauseman">PMID:35830882</ref>. This dephosphorylation event allows for pathway activation <ref name="Liau">PMID: 35768504</ref>. 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. PP1C binds to SHOC2 and MRAS-GTP in a specific orientation that doesn’t change the conformation of the {{Font color|red|catalytic site}} and leaves it accessible for substrate binding as shown in '''Figure 2''' in red. | <scene name='95/952695/Pp1cintro/3'>The Protein Phosphatase Complex 1 (PP1C)</scene> subunit contains the catalytic site of the SMP complex. PP1C is a [https://pubmed.ncbi.nlm.nih.gov/30036567/. 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 Mn⁺² and 1 Cl⁻¹ present that coordinate [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3458771/. nucleophilic] water molecules in the active site <ref name="Hauseman">PMID:35830882</ref>. This dephosphorylation event allows for pathway activation <ref name="Liau">PMID: 35768504</ref>. 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. PP1C binds to SHOC2 and MRAS-GTP in a specific orientation that doesn’t change the conformation of the {{Font color|red|catalytic site}} and leaves it accessible for substrate binding as shown in '''Figure 2''' in red. | ||
PP1C binds to SHOC2 through a hydrophobic N-terminal disordered region that is complimentary to the <scene name='95/952695/Rvxf_motif/2'>RVXF Motif on SHOC2</scene> and adjacent to a catalytic metal ions <ref name="Liau">PMID: 35768504</ref>. In the RAS/RAF signaling cascade, the region of RAF that is C-terminal to the phosphate group binds to this hydrophobic groove, and the remaining residues bind to the hydrophobic region of SHOC2 <ref name="Hauseman">PMID:35830882</ref>. RAF binding to this region of SHOC2 is what allows PP1C to be specific when in the SMP complex in comparison to PP1C on its own <ref name="Hauseman">PMID:35830882</ref>. Similarly to SHOC2, PP1C does not undergo a <scene name='95/952694/Pp1coverlay/4'>significant conformational change</scene> 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 <scene name='95/952695/Rvxf_motif/2'>RVXF Motif on SHOC2</scene> and adjacent to a catalytic metal ions <ref name="Liau">PMID: 35768504</ref>. In the RAS/RAF signaling cascade, the region of RAF that is C-terminal to the phosphate group binds to this hydrophobic groove, and the remaining residues bind to the hydrophobic region of SHOC2 <ref name="Hauseman">PMID:35830882</ref>. RAF binding to this region of SHOC2 is what allows PP1C to be specific when in the SMP complex in comparison to PP1C on its own <ref name="Hauseman">PMID:35830882</ref>. Similarly to SHOC2, PP1C does not undergo a <scene name='95/952694/Pp1coverlay/4'>significant conformational change</scene> 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>. | ||