| Literature References | 1. LINDER, M.E. AND GILMAN, A.G.
G proteins.
SCI.AM. 70-77 (1993).
2. KAZIRO, Y., ITOH, H., KOZASA, T., NAKAFUKU, M. AND SATOH, T.
Structure and function of signal-transducing GTP-binding proteins.
ANNU.REV.BIOCHEMISTRY 60 349-400 (1991).
3. SIMON, M.I., STRATHMANN, M.P. AND GAUTAM, N.
Diversity of G proteins in signal transduction.
SCIENCE 252 802-808 (1993).
4. CLAPHAM, D.E. AND NEER, E.J.
New roles for G protein beta-gamma dimers in transmembrane signalling.
NATURE 365 403-406 (1993)
5. LUPAS, A.N., LUPAS, J.M. AND STOCK, J.B.
Do G protein subunits associate via a 3-stranded coiled coil?
FEBS LETT. 314 105-108 (1992).
6. SOHMA, H., HASHIMOTO, H., HIRAIKE, N., OHGURO, H. AND AKINO, T.
Different functional forms of G protein beta-gamma subunits, beta-gamma-I
and beta-gamma-II, in bovine brain.
BIOCHIM.BIOPHYS.ACTA 1178(1) 111-116 (1993).
7. SOHMA, H., HASHIMOTO, H., HIRAIKE, N., OHGURO, H. AND AKINO, T.
Identification of a novel gamma-subunit from bovine brain GTP-binding
regulatory proteins (GI/O).
BIOCHEM.BIOPHYS.RES.COMMUN. 190(3) 849-856 (1993).
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| Documentation | Guanine nucleotide binding proteins (G proteins) are a family of membrane-
associated proteins that couple extracellularly-activated integral-membrane
receptors to intracellular effectors, such as ion channels and enzymes that
vary the concentration of second messenger molecules [1-3]. G proteins are
composed of 3 subunits (alpha, beta and gamma) which, in the resting state,
associate as a trimer at the inner face of the plasma membrane. The alpha
subunit has a molecule of guanosine diphosphate (GDP) bound to it:
stimulation of the G protein by an activated receptor leads to its exchange
for GTP (guanosine triphosphate). This results in the separation of the
alpha from the beta and gamma subunits, which always remain tightly
associated as a dimer. Both the alpha and beta-gamma subunits are then able
to interact with effectors, either individually or in a cooperative manner.
The intrinsic GTPase activity of the alpha subunit hydrolyses the bound GTP
to GDP. This returns the alpha subunit to its inactive conformation and
allows it to reassociate with the beta-gamma subunit, thus restoring the
system to its resting state.
Although originally thought to be a passive attenuator and membrane anchor
for the activated alpha subunit, the beta-gamma subunit is now recognised
as playing an active role in a number of different G protein-coupled
signalling events [4]. It has been shown to modulate the activity of some
isoforms of adenylyl cyclase, phospholipase C, and some ion channels. It is
involved in receptor phosphorylation via specific kinases, and has been
implicated in the p21ras-dependent activation of the MAP kinase cascade.
It is also highly likely that it contributes to the recognition of specific
receptors by the G protein. No atomic structure is yet available for beta-
gamma subunits, but it has been proposed that they interact both with each
other and with other proteins via a coiled coil motif in their N-terminal
regions [5].
Five distinct mammalian G protein gamma subunits have been cloned, and
others have been identified but not fully characterised [6,7]: they have
also been identified in Drosophila and Loligo forbesi. The proteins contain
70-90 amino acids, with apparent molecular weights of 6-12 kDa. Their
primary structures are notably more variable than those of the beta sub-
units. Gamma subunits are post-translationally modified by isoprenylation
and carboxyl-methylation of a cysteine residue 4 amino acids from the C-
terminus - this appears to be essential for the interaction of the beta-
gamma subunit with the membrane and with other proteins.
GPROTEING is a 3-element fingerprint that provides a signature for the
gamma-transducins. The fingerprint was derived from an initial alignment of
5 sequences: the motifs were drawn from conserved regions spanning the full
alignment length. A single iteration on OWL21.1 was required to reach
convergence, no further sequences being identified beyond the starting set.
An update on SPTR37_9f identified a true set of 17 sequences.
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| Sequence Titles | GBG1_BOVIN GUANINE NUCLEOTIDE-BINDING PROTEIN G(T) GAMMA-1 SUBUNIT (TRANSDUCIN GAMMA CHAIN) - BOS TAURUS (BOVINE).
GBG1_HUMAN GUANINE NUCLEOTIDE-BINDING PROTEIN G(T) GAMMA-1 SUBUNIT (TRANSDUCIN GAMMA CHAIN) - HOMO SAPIENS (HUMAN), AND CANIS FAMILIARIS (DOG).
GBG2_BOVIN GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-2 SUBUNIT (G GAMMA-I) - BOS TAURUS (BOVINE).
GBG3_BOVIN GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-3 SUBUNIT - BOS TAURUS (BOVINE), AND MUS MUSCULUS (MOUSE).
GBG4_HUMAN GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-4 SUBUNIT - HOMO SAPIENS (HUMAN).
GBG4_MOUSE GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-4 SUBUNIT - MUS MUSCULUS (MOUSE).
GBG5_HUMAN GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-5 SUBUNIT - HOMO SAPIENS (HUMAN), MUS MUSCULUS (MOUSE), RATTUS NORVEGICUS (RAT), AND BOS TAURUS (BOVINE).
GBG7_BOVIN GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-7 SUBUNIT (GAMMA-II) - BOS TAURUS (BOVINE).
GBG7_HUMAN GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-7 SUBUNIT - HOMO SAPIENS (HUMAN).
GBG7_RAT GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-7 SUBUNIT - RATTUS NORVEGICUS (RAT).
GBG8_BOVIN GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-8 SUBUNIT (G GAMMA-C) - BOS TAURUS (BOVINE).
GBG8_HUMAN GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-8 SUBUNIT (G GAMMA-C) - HOMO SAPIENS (HUMAN).
GBG9_RAT GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-9 SUBUNIT (GAMMA-8) - RATTUS NORVEGICUS (RAT).
GBGA_HUMAN GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-10 SUBUNIT - HOMO SAPIENS (HUMAN).
GBGB_HUMAN GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-11 SUBUNIT - HOMO SAPIENS (HUMAN).
GBGC_BOVIN GUANINE NUCLEOTIDE-BINDING PROTEIN G(I)/G(S)/G(O) GAMMA-12 SUBUNIT (GAMMA-S1) - BOS TAURUS (BOVINE).
GBG_CAEEL PROBABLE GUANINE NUCLEOTIDE-BINDING PROTEIN GAMMA SUBUNIT - CAENORHABDITIS ELEGANS.
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