Mechanisms of Ras Membrane Organization and Signaling: Ras Rocks Again

Abstract

Ras is the most frequently mutated oncogene and recent drug development efforts have spurred significant new research interest. Here we will review progress toward understanding how Ras functions in nanoscale, proteo-lipid signaling complexes on the plasma membrane, called nanocluster. We will discuss how G-domain reorientation is plausibly linked to Ras-nanoclustering and -dimerization. We will then look at how these mechanistic features could cooperate in the engagement and activation of RAF by Ras. Moreover, we will show how this structural information can be integrated with microscopy data that provide nanoscale resolution in cell biological experiments. Synthesizing the available data, we propose to distinguish between two types of Ras nanoclusters, an active, immobile RAF-dependent type and an inactive/ neutral membrane anchor-dependent. We conclude that it is possible that Ras reorientation enables dynamic Ras dimerization, while the whole Ras/ RAF complex transits into an active state. These transient di/oligomer interfaces of Ras may be amenable to pharmacological intervention. We close by highlighting a number of open questions including, whether all effectors form active nanoclusters and whether there is an isoform specific composition of Ras nanocluster.

Machine learning–driven multiscale modeling reveals lipid-dependent dynamics of RAS signaling proteins

“…There is substantial interest in assessing the ability of RAS molecules to dimerize ( 11 – 13 ) or colocalize ( 14 – 17 ) at the membrane, because RAS-dependent RAF activation requires dimerization of RAF ( 18 – 20 ). Although wild-type KRAS4b, a common splice variant of KRAS (hereafter referred to as RAS), does not dimerize on two-component supported lipid bilayers ( 21 ), it preferentially colocalizes with anionic lipids in the liquid-disordered domains of giant unilamellar vesicles ( 22 ) and clusters on the scale of tens of nanometers in extracted PM sheets ( 14 , 23 , 24 ).…”

Evaluation of K-Ras4B dimer interfaces and the role of Raf effectors

“…20,24,[48][49][50][51][52][53] Dimerization is critical for the activity of WT K-Ras as well as for the oncogenic ability of mutant G12D K-Ras. 60 Ras dimers have been observed in the biological assembly of an X-ray crystal structure 64 and NMR-inspired structures, 61 and different dimer interfaces have been suggested using both computational and experimental methods for members of the Ras family, 52,53 but still the exact structure of the KRAS dimer has not been experimentally resolved in the presence of its effector proteins.…”

“…3 Recently, another approach for targeting K-Ras4B arose from cumulative evidence that membrane-bound K-Ras proteins, including K-Ras4B, form dimers or even nanoclusters in order to activate signaling pathways, with the dimer proposed to be the basic clustering unit. 20,24,[48][49][50][51][52][53] K-Ras dimerization aids the regulation of signaling pathways by providing signaling specificity, allosteric effects, and effector activation and inhibition. Indeed, it has been shown that WT K-Ras acts as a tumor suppressor in KRAS mutant cancer cells 54 by antagonizing the function of oncogenic K-Ras when forming WT-mutant dimers, which however no longer occurs when the WT KRAS allele is lost during tumor progression.…”

“…At the same time, Ras dimers have been observed in the biological assembly of an X-ray crystal structure 64 and NMR-inspired structures. 61 Different dimer interfaces have been suggested using both computational and experimental methods for members of the Ras family, 52,53 proposing several interfaces for membrane-bound Ras dimers such as the region between the α4-α5 helices and the loop between β2-β3 sheets for N-Ras, 48,65 the α4-β6-α5 helical interface for H-Ras, 51 the α4-α5 interface for K-Ras, 60,61,64 the β2 strands or the α3-α4 helical interface for K-Ras, 20,[66][67][68] and dimer assemblies with GTP in the interface for K-Ras. 69,70 For the K-Ras4B G12D mutant similar interfaces have also been observed; the β2 interface in crystal structures of the K-Ras4B G12D mutant (PDB ID: 7ACF 71 , 6GJ7 72 ) as well as the α4-α5 interface (PDB ID 5US4 73 , 5XCO 74 ).…”

Внутрішньоклітинні Механізми Дії Гормонів. Сучасний Погляд На Проблему І Перспективи

“…Білок SOS здійснює переведення Ras в активну GTP-форму. Протилежний процес -гідроліз GTP і переведення Ras у неактивну форму -GDP-Ras, знаходиться під контролем білка-активатора GTP-азної активності GAP (GTPase-Activating Protein) [32,33]. Сенс такої складної системи регуляції зрозумілий -адже активація/інактивація Ras лежить в основі процесів, здатних ініціювати, залежно від обставин, процес поділу клітин або механізму загибелі клітини шляхом апоптозу.…”