#gpcr

That is a great question! The advancements of Maoism can be split into two main categories. The first category is the qualitative advancements with build on the core of Marxism, and mark the transformation of Marxism-Leninism into Marxism-Leninism-Maoism. The second is the advances which advance Maoism itself, but do not propel revolutionary science into a qualitatively higher stage.

In terms of the first category, three main advancements were made which qualitatively advanced the knowledge of revolutionary science along the lines of the three essential aspects of Marxism. These were made during the 3rd world historic revolution, that being the Chinese Revolution, up till the end of the Great Proletarian Cultural Revolution. These are;

Advancements in the field of Political Economy: Chairman Mao Zedung was the first to seriously advance the study of imperialism beyond the great discoveries of Lenin and analyze Imperialism in it's modern Semi-Colonial form. This investigation led to the discovery of Bureaucrat-Comprador Capitalism and Semi-Feudalism, the ruling classes within Semi-Colonies.

Advancements in the field of Class Struggle 1: Following the analysis of Bureaucrat-Comprador Capitalism and Semi-Feudalism, along with analysis of both the RUssian and Chinese Revolution's, Mao discovered a crucial revolutionary stage for all countries under the boot of feudalism and imperialism, that of the New Democratic Revolution. The NDR is a national revolution against Feudalism and Imperialism headed principally by the Proletariat, in alliance with all progressive classes of society, including the national bourgeoises (For example the CPC-Kuomintang united fount against the Japanese, or the united front against the Tzar in Russia) The NDR must be completed before socialist revolution can occur.

Advancements in the field of Class Struggle 2: Another Key advancement of Mao was the discovery that, contrary to popular opinion at the time, class struggle continues under socialism. Under socialism new bureaucratic bourgeoisie emerge from within the party and state structure (following the principle of one dividing into two) and from remaining inequalities in society (following the principle of unequal development). Following the defeat of soviet socialism buy such forces and the rise of Khrushchevite Revisionism, and even the rise of such Revisionism in the CPC, Mao and the socialist line in the party waged a struggle against Khrushchtevite Revisionism and later internal revolution, culminating with the Great Proletarian Cultural Revolution. The GPCR targeted both old feudal and capitalist structures as well as the new bourgeoisie who promoted the capitalist line in the party, and pushed the development of socialism to its farthest point so far (which is why it the 3rd world historic revolution).

Advancements in the field of Dialectical Materialism: Mao's book On Contradictions is edental reading for any serious communist, it contains Mao's contribution to the philosophical foundations of Marxism. It puts forward key concepts such as the relationship between antagonistic and non antagonistic contradiction, differentiates between principle and secondary contractions, and the universality and particularity of contractions. Mao also puts forward in other works how contractions should be handled. Contradictions amongst the people vs contradictions with ractionares, and importantly contractions between the masses and the party, which is solved with the mass line.

Video: Workers of the Shanghai Generator Factory Discuss Marxist Philosophy (1976)

But after the Shanghai Commune, factional struggles and allegations against and death of Lin Piao surfaced, policy shifts were initiated by a Centrist-Rightist combination veering away from the proletarian class struggle and leading to the Nixon diplomatic visit, the rehabilitation and promotion of Deng Xiaoping, reinterpretations of the GPCR and the three-worlds theory by Deng and the increasing calls for modernization through capitalist reforms and opening up for integration with the US and world capitalist system.

After the death of Chou Enlai in February 1976, Deng was removed from office for promoting big comprador ideology. But after the death of Mao in September 1976, the October coup resulted in the arrest and imprisonment of the so-called Gang of Four by the combination of Hua Guofeng and Deng.

After the latter gained the upper hand over the former who resigned, the GPCR was declared a complete catastrophe, Mao no less was castigated for it and millions of CPC cadres and members were expelled. Liu Xiaoqi the No. 1 capitalist-roader was rehabilitated. The communes were dismantled and public assets were privatized in earnest. The sweat shop operations for the US market began.

China’s Great Proletarian Cultural Revolution was launched 55 years ago, on May 16, 1966.

Marxist leader Sam Marcy wrote groundbreaking analysis of the GPCR as it was unfolding, drawing on the experience of the French and Soviet revolutions. Here is one of his most important pieces:

“… it is the first time, since the early days of the Great October Socialist Revolution, that the leadership of a socialist country picked up the threads of the Paris Commune and made an earnest effort not only to crush the old state machine, but to do away altogether with those elements of the bureaucratic apparatus of the old order. These are the elements which every socialist state to one extent or another has inherited from the past and in the course of trying to reconstruct society on a new basis, found necessary to utilize for immediate practical purposes. But as time passed, such societies were either unwilling or unable to cast them off. China’s effort is all the more remarkable because of the tremendous struggle launched to carry this out by projecting the masses on to the political arena and attempting to awaken their creative initiative in completing the revolution.”

G-protein-coupled receptors (GPCRs) are the largest and most diverse group of membrane receptors in eukaryotes. 

Structure

single polypeptide chain comprising of seven transmembrane α-helices

extracellular N-terminal domain of varying length, 

intracellular C-terminal domain.

length of the extracellular N terminus and the location of the agonist binding domain determines family.

The long, third cytoplasmic loop couples to the G-protein 

Usually particular receptor subtypes couple selectively with particular G-proteins

For small molecules, such as noradrenaline, the ligand-binding domain of class A receptors is buried in the cleft between the α-helical segments within the membrane. Peptide ligands bind more superficially to the extracellular loops

G protein system

GPCRs interact with G proteins in the plasma membrane when an external signaling molecule binds to a GPCR, causes a conformational change in the GPCR.  G-proteins comprise a family of membrane-resident proteins whose function is to recognise activated GPCRs and pass on the message to the effector systems that generate a cellular response. 

G proteins are specialized proteins with the ability to bind the nucleotides guanosine triphosphate (GTP) and guanosine diphosphate (GDP). 

The G proteins that associate with GPCRs are heterotrimeric, (alpha beta and gamma subunits)

 alpha and gamma are attached to the plasma membrane by lipid anchors 

Trimer in resting state 

activated alpha monomer and beta/gamma dimer

Guanine nucleotides bind to the α subunit, which has enzymic activity, catalysing the conversion of GTP to GDP. The β and γ subunits remain together as a βγ complex. All three subunits are anchored to the membrane through a fatty acid chain, coupled to the G-protein through a reaction known as prenylation.

G-proteins are freely diffusible so a single pool of G-protein in a cell can interact with several different receptors and effectors 

When GPCR is activated by an agonist, a conformational change causes it to acquire high affinity for αβγ (G protein)

bound GDP dissociates and is replaced with GTP, which in turn causes dissociation of the G-protein trimer, releasing α-GTP and βγ subunits - the ‘active’ forms of the G-protein

which diffuse in the membrane and can associate with various enzymes and ion channels

Signalling is terminated on hydrolysis of GTP to GDP through the GTPase activity of the α subunit.

resulting α–GDP dissociates from the effector, and reunites with βγ

Attachment of the α subunit to an effector molecule increases its GTPase activity

GTP hydrolysis is termination --> activation of the effector tends to be self-limiting

Second messenger targets for G proteins

Main targets:

Adenylyl cyclase (responsible for cAMP formation)

Phospholipase C (inositol phosphate and diacylglycerol (DAG) formation)

Ion channels, particularly calcium and potassium channels

Rho A/Rho kinase (system controlling the activity of many signalling pathways for cell growth and proliferation, smooth muscle contraction, etc.)

Mitogen-activated protein kinase (MAP kinase) system controlling cell functions eg division.