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G-proteins

2010-11-24T09:54:19Z

090105353:

[[Guanine nucleotide|Guanine nucleotide]] binding [[Protein|protein]] that binds [[GTP|GTP]] when activated, which it hydrolyses to [[GDP|GDP]].  The active form of the [[Protein|protein]] can interact with a number of down stream effectors such as [[Adenylyl cyclase|adenylyl cyclase]] (producing [[CAMP|cAMP]] from [[ATP|ATP]]), and [[Phospholipase C|phospholipase C]] ([[PLC|PLC]]).

The [[G-proteins|G-proteins]] can be divided in to two families - the [[Heterotrimeric G-proteins|heterotrimeric G-proteins]] and the small or [[Mono-meric G-proteins|mono-meric G-proteins]]. 

G-protein coupled receptors ([[GPCR|GPCR]]) upon binding of [[Stimulus|stimulus]] activates G-protein.

The structure of a [[GPCR|GPCR]] shows 7 transmembrane spans, with 3 exoloops and 4 cytoloops. The N-terminal is found on the outside of the membrane and the C-terminal found on the cytosolic side of the membrane.

=== G protein families ===

There are 4 major families of [[Heterotrimeric G-proteins|heterotrimeric G-protein]]. The G-proteins are divided based on the homology of alpha subunit. Each receptor only affects one type of G-protein. <ref name="Alberts et al.,2008: 919">Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Robers and Peter Walter(2008) Molecular Biology of The Cell, 5th edition, USA: Garland Science. pg 919</ref>

There are 20 alpha subunits, 6 beta subunits and 12 gamma subunits in human that make up the diversity of G-proteins.

Heterotrimeric G-proteins contain three subunits: [[alpha|alpha]], [[beta|beta]] and [[gamma|gamma]]. In the inactive form, all three subunits are associated together and [[GDP|GDP]] binds to the alpha subunit. On activation, there is a conformational change in the alpha subunit, which now binds to [[GTP|GTP]] and disocciates from the [[beta-gamma complex|beta-gamma complex]]. The alpha subunit and beta-gamma complex can now interact with different effectors to bring about a response. The [[GTPase|GTPase]] activity of the alpha subunit causes the loss of [[GTP|GTP]] from the binding site in the alpha subunit, and another [[GDP|GDP]] binds, resetting the system <ref>Alberts et al., Molecular Biology Of The Cell, Fifth Edition</ref>.

==== Family I ====

Consists of [[Gs|G]][[Gs|s]] and [[Golf|G]][[Golf|olf]]. The alpha subunit mediates the function in both G-proteins. Gs activates [[Adenylyl cyclase|adenylyl cyclase]] and [[Calcium ion channels|Calcium ion channels]] while Golf activates [[Adenylyl cyclase|adenylyl cyclase]] in olfactory sensory neurons.

==== Family II ====

Consists of [[Gi|G]][[Gi|i]], [[Go|G]][[Go|o]] and [[Gt|G]][[Gt|t]]. The alpha subunit of Gi inhibits [[Adenylyl cyclase|adenylyl cyclase]] while the beta-gamma complex of Gi activates potassium ion channels. For Go, the beta-gamma complex activates [[Potassium ion channels|Potassium ion channels]] and at the same time inactivates [[Calcium ion channel|Calcium ion channel]]. Both alpha subunit and beta-gamma complex of Go activate [[Phospholipase C|phospholipase C]]-beta. The alpha subunit of Gt activates [[Cyclic GMP|cyclic GMP]] [[Phosphodiesterase|phosphodiesterase]] in vertebrate [[Rod photoreceptors|rod photoreceptors]].

==== Family III ====

Consists of [[Gq|G]][[Gq|q]]. The alpha subunit of Gq functions to activate [[Phospholipase C|phospholipase C]]-beta.

==== Family IV ====

Consists of [[G12/13|G]][[G12/13|1]][[G12/13|2/13]]. The action of alpha subunit of G12/13 is to activate [[Rho|Rho]] family monomeric [[GTPase|GTPase]]. 

=== References''':''' ===

<references />

G-proteins

2010-11-23T22:13:07Z

090105353:

[[Guanine nucleotide|Guanine nucleotide]] binding [[Protein|protein]] that binds [[GTP|GTP]] when activated, which it hydrolyses to [[GDP|GDP]].  The active form of the [[Protein|protein]] can interact with a number of down stream effectors such as [[Adenylyl cyclase|adenylyl cyclase]] (producing [[CAMP|cAMP]] from [[ATP|ATP]]), and [[Phospholipase C|phospholipase C]] ([[PLC|PLC]]).

The [[G-proteins|G-proteins]] can be divided in to two families - the [[Heterotrimeric G-proteins|heterotrimeric G-proteins]] and the small or [[Mono-meric G-proteins|mono-meric G-proteins]]. 

G-protein coupled receptors ([[GPCR|GPCR]]) upon binding of [[Stimulus|stimulus]] activates G-protein.

The structure of a [[GPCR|GPCR]] shows 7 transmembrane spans, with 3 exoloops and 4 cytoloops. The N-terminal is found on the outside of the membrane and the C-terminal found on the cytosolic side of the membrane.

=== G protein families ===

There are 4 major families of [[Heterotrimeric G-proteins|heterotrimeric G-protein]]. The G-proteins are divided based on the homology of alpha subunit. Each receptor only affects one type of G-protein. <ref name="Alberts et al.,2008: 919">Bruce Alberts, Alexander Johnson, Julian Lewis, Martin Raff, Keith Robers and Peter Walter(2008) Molecular Biology of The Cell, 5th edition, USA: Garland Science. pg 919</ref>

There are 20 alpha subunits, 6 beta subunits and 12 gamma subunits in human that make up the diversity of G-proteins.

Heterotrimeric G-proteins contain three subunits: alpha, beta and gamma. In the inactive form, all three subunits are associated together and GDP binds to the alpha subunit. On activation, there is a conformational change in the alpha subunit, which now binds to GTP and disocciates from the beta-gamma complex. The alpha subunit and beta-gamma complex can now interact with different effectors to bring about a response. The GTPase activity of the alpha subunit causes the loss of GTP from the binding site in the alpha subunit, and another GDP binds, resetting the system.<references />Alberts et al., Molecular Biology Of The Cell, Fifth Edition

==== Family I ====

Consists of Gs and Golf. The alpha subunit mediates the function in both G-proteins. Gs activates [[Adenylyl cyclase|adenylyl cyclase]] and [[Calcium ion channels|Calcium ion channels]] while Golf activates [[Adenylyl cyclase|adenylyl cyclase]] in olfactory sensory neurons.

==== Family II ====

Consists of Gi, Go and Gt. The alpha subunit of Gi inhibits [[Adenylyl cyclase|adenylyl cyclase]] while the beta-gamma complex of Gi activates potassium ion channels. For Go, the beta-gamma complex activates [[Potassium ion channels|Potassium ion channels]] and at the same time inactivates [[Calcium ion channel|Calcium ion channel]]. Both alpha subunit and beta-gamma complex of Go activate [[Phospholipase C|phospholipase C]]-beta. The alpha subunit of Gt activates [[Cyclic GMP|cyclic GMP]] [[Phosphodiesterase|phosphodiesterase]] in vertebrate [[Rod photoreceptors|rod photoreceptors]].

==== Family III ====

Consists of Gq. The alpha subunit of Gq functions to activate [[Phospholipase C|phospholipase C]]-beta.

==== Family IV ====

Consists of G12/13. The action of alpha subunit of G12/13 is to activate Rho family monomeric [[GTPase|GTPase]]. 

=== References''':''' ===

<references />

G-protein Coupled Receptor

2010-11-11T10:56:58Z

090105353:

 A [[Seven|seven]] [[Transmembrane|transmembrane]] spanning [[Receptor|receptor]] that interacts with [[G-proteins|G-proteins]]. G-proteins are composed of three subunits: alpha, beta and gamma. In the inactive state, the alpha subunit binds to [[GDP|GDP]], and in the active state, GDP is released and [[GTP|GTP]] binds. The alpha subunit disocciates from the beta-gamma complex, and then both can activate separate effectors.

G-protein Coupled Receptor

2010-11-11T10:56:30Z

090105353:

 A [[Seven|seven]] [[Transmembrane|transmembrane]] spanning [[Receptor|receptor]] that interacts with [[G-proteins|G-proteins]]. G-proteins are composed of three subunits: alpha, beta and gamma. In the inactive state, the alpha subunit binds to GDP, and in the active state, GDP is released and GTP binds. The alpha subunit disocciates from the beta-gamma complex, and then both can activate separate effectors.