From Proteopedia

Revision as of 20:46, 27 March 2023

Surface representation of SHOC2-PP1C-MRAS designed in PyMol from PDB.Blue is SHOC2, Orange is PP1C and green is MRAS.

Introduction

Structural Introduction

The enzyme requires 3 domains (SHOC-2(blue), PP1C(coral), and MRAS (green)) to form the active enzyme (SMP Complex), also known as a ^[1]. SHOC-2 is a scaffolding protein that holds the other subunits in the correct orientation, allowing for the holoenzyme to be functional. PP1C is a catalytic domain of a phosphatase enzyme PP1[1], which cleaves ____. MRAS is a GTPase protein and is located near (typically just below) the cell membrane. When MRAS binds GTP, it becomes active and triggers the assembly of the active holoenzyme^[1]. The SMP complex was determined via cryo-electron microscopy as well as x-ray diffraction. These studies found that PP1C and MRAS occupy the concave surface of SHOC2, leaving the catalytic site of PP1C and the substrate binding cleft in MRAS exposed.

Biological Introduction

SHOC2-PP1C-MRAS is a human enzyme that is involved in regulating cell proliferation and division^[2]. The enzyme is involved in the vast RAS-MAPK pathway, which is initially activated by an extracellular growth factor binding to a membrane bound RAS GTPase[2] such as HRAS, NRAS, or KRAS. RAS-GTPases are a family of proteins that work by functioning as molecular switches[3]. This occurs from the protein alternating between binding GTP to be active and GDP to be inactive ^[2]. After activation via an extracellular growth factor, the RAS-GTPase enzyme binds GTP, which activates RAF^[3].

This is a default text for your page '. Click above on edit this page' to modify. Be careful with the < and > signs. You may include any references to papers as in: the use of JSmol in Proteopedia ^[4] or to the article describing Jmol ^[5] to the rescue.

Structure

Special Interactions

SHOC2

leucine rich repeat domain

PP1C

protein phosphatase 1 catalytic subunit

MRAS

does not bind PP1C in absence of SHOC2

Switch I and II

Switch I and II are located on MRAS. The switches determine whether MRAS can bind to SHOC2-PP1C. The switches have to go through a conformational change to allow binding of SHOC2-PP1C to MRAS. This conformational change is caused by GTP replacing GDP. Once GTP is added MRAS shifts and binds with SHOC2. When GDP is bound to MRAS switch II is moved outward which causes a steric clash with SHOC2 . When GTP is bound, switch II can form various hydrophobic interactions with SHOC2^[6]. . Interactions are strengthened with hydrogen bonding and pi stacking. When MRAS is bound to SHOC2-PP1C, switch I has an important role in making interactions with PP1C.

Binding Pocket

Once all the domains are bound NTpS binds to PP1C in the active site. Once the NTpS is bound it becomes dephosphorylated and the complex falls apart. NTpS is dephosphorylated to prevent the active dimeric RAF from inactivating and changing into its monomeric structure. The NTpS active site is surrounded by hydrophobic and acidic regions along with C-terminal. (). These regions are located on the surface of PP1C whereas the active site is placed further into the structure. It is thought that these regions help the ligand bind to the active site by making interactions that will lead NTpS into the protein. There is still some uncertainty as to how the substrate selectivity works but these regions could play an essential role in it. Specifically, the C-terminal of the pS from NTpS would bind to the hydrophobic region on PP1C^[7].

NTpS can bind to the PP1C active site without PP1C also being bound to SHOC2 and MRAS, however the catalytic activity is much slower and the reaction is less efficient. Also for this event to occur NTpS would need to be exposed from its binding site in the inactive RAF complex. A RAS has to bind to RAF to expose the NTpS allowing PP1C and NTpS to bind.

Biological Function

Relevance

Inhibitors

Medical Conditions

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References

1. ↑ ^{1.0 1.1} Hauseman, Z.J., Fodor, M., Dhembi, A. et al. Structure of the MRAS–SHOC2–PP1C phosphatase complex. Nature 609, 416–423 (2022). doi: 10.1038/s41586-022-05086-1. DOI:10.1038/s41586-022-05086-1.
2. ↑ ^{2.0 2.1} Bernal Astrain G, Nikolova M, Smith MJ. Functional diversity in the RAS subfamily of small GTPases. Biochem Soc Trans. 2022 Apr 29;50(2):921-933. doi: 10.1042/BST20211166. DOI:10.1042/BST20211166.
3. ↑ Molina JR, Adjei AA. The Ras/Raf/MAPK pathway. J Thorac Oncol. 2006 Jan;1(1):7-9. DOI:10.1016/S1556-0864(15)31506-9.
4. ↑ Hanson, R. M., Prilusky, J., Renjian, Z., Nakane, T. and Sussman, J. L. (2013), JSmol and the Next-Generation Web-Based Representation of 3D Molecular Structure as Applied to Proteopedia. Isr. J. Chem., 53:207-216. doi:http://dx.doi.org/10.1002/ijch.201300024
5. ↑ Herraez A. Biomolecules in the computer: Jmol to the rescue. Biochem Mol Biol Educ. 2006 Jul;34(4):255-61. doi: 10.1002/bmb.2006.494034042644. PMID:21638687 doi:10.1002/bmb.2006.494034042644
6. ↑ Daniel A. Bonsor, Patrick Alexander, Kelly Snead, Nicole Hartig, Matthew Drew, Simon Messing, Lorenzo I. Finci, Dwight V. Nissley, Frank McCormick, Dominic Esposito, Pablo Rodrigiguez-Viciana, Andrew G. Stephen, Dhirendra K. Simanshu. Structure of the SHOC2–MRAS–PP1C complex provides insights into RAF activation and Noonan syndrome. bioRxiv. 2022.05.10.491335. doi: 10.1101/2022.05.10.491335. DOI:10.1101/2022.05.10.491335.
7. ↑ Liau NPD, Johnson MC, Izadi S, Gerosa L, Hammel M, Bruning JM, Wendorff TJ, Phung W, Hymowitz SG, Sudhamsu J. Structural basis for SHOC2 modulation of RAS signalling. Nature. 2022 Jun 29. pii: 10.1038/s41586-022-04838-3. doi:, 10.1038/s41586-022-04838-3. PMID:35768504 doi:http://dx.doi.org/10.1038/s41586-022-04838-3