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PR01131

Identifier
CONNEXIN36  [View Relations]  [View Alignment]  
Accession
PR01131
No. of Motifs
3
Creation Date
24-MAY-1999
Title
Connexin36 (Cx36) signature
Database References
PRINTS; PR00206 CONNEXIN
PRODOM; PD020274; PD020276
INTERPRO; IPR002260
Literature References
1. PHELAN, P., BACON, J.P., DAVIES, J.A., STEBBINGS, L.A., TODMAN, M.G.,
AVERY, L., BAINES, R.A., BARNES, T.M., FORD, C., HEKIMI, S., LEE, R.,
SHAW, J.E., STARICH, T.A., CURTIN, K.D., SUN, Y. AND WYMAN, R.J.
Innexins: a family of invertebrate gap-junction proteins.
TRENDS GENET. 14 348-349 (1998).
 
2. DERMIETZEL, R. AND SPRAY, D.C.
Gap junctions in the brain: where, what type, how many and why?
TRENDS NEUROSCIENCE 16 186-192 (1993).
 
3. GOODENOUGH, D.A., GOLIGER, J.A. AND PAUL, D.L.
Connexins, connexons, and intercellular communication.
ANNU.REV.BIOCHEMISTRY 65 475-502 (1996).
 
4. KUMAR, N.M. AND GILULA, N.B.
The gap junction communication channel.
CELL 84 381-388 (1996).
 
5. KUMAR, N.M. AND GILULA, N.B.
Molecular biology and genetics of gap junction channels.
SEMIN.CELL BIOL. 3 3-16 (1992).
 
6. NICHOLSON, S.M. AND BRUZZONE, R.
Gap junctions: getting the message through.
CURR.BIOL. 7 340-344 (1997).
 
7. SIMON, A.M. AND GOODENOUGH, D.A.
Diverse functions of vertebrate gap junctions.
TRENDS CELL BIOL. 8 477-483 (1998).
 
8. SPRAY, D.C. AND DERMIETZEL, R.
X-linked dominant Charcot-Marie-Tooth disease and other potential gap-
junctions diseases of the nervous system.
TRENDS NEUROSCIENCE 18 256-262 (1995).
 
9. CONDORELLI, D.F., PARENTI, R., SPINELLA, F., TROVATO SALINARO, A.,
BELLUARDO, N., CARDILE, V. AND CICIRATA, F.
Cloning of a new gap junction gene (Cx36) highly expressed in mammalian
brain neurons.
EUR.J.NEUROSCIENCE 10 1202-1208 (1999).

Documentation
The connexins are a family of integral membrane proteins that oligomerise
to form intercellular channels that are clustered at gap junctions. These
channels are specialised sites of cell-cell contact that allow the passage
of ions, intracellular metabolites and messenger molecules (with molecular
weight <1-2 kDa) from the cytoplasm of one cell to its apposing neighbours.
They are found in almost all vertebrate cell types, and somewhat similar
proteins have been cloned from plant species. Invertebrates utilise a 
different family of molecules, innexins, that share a similar predicted 
secondary structure to the vertebrate connexins, but have no sequence 
identity to them [1].
 
Vertebrate gap junction channels are thought to participate in diverse
biological functions. For instance, in the heart they permit the rapid 
cell-cell transfer of action potentials, ensuring coordinated contraction 
of the cardiomyocytes. They are also responsible for neurotransmission at
specialised `electrical' synapses. In non-excitable tissues, such as the 
liver, they may allow metabolic cooperation between cells. In the brain,
glial cells are extensively-coupled by gap junctions; this allows waves of
intracellular Ca2+ to propagate through nervous tissue, and may contribute
to their ability to spatially-buffer local changes in extracellular K+ 
concentration [2].
 
The connexin protein family is encoded by at least 13 genes in rodents, with
many homologues cloned from other species. They show overlapping tissue 
expression patterns, most tissues expressing more than one connexin type.
Their conductances, permeability to different molecules, phosphorylation and
voltage-dependence of their gating, have been found to vary. Possible
communication diversity is increased further by the fact that gap junctions
may be formed by the association of different connexin isoforms from 
apposing cells. However, in vitro studies have shown that not all possible
combinations of connexins produce active channels [3,4].
 
Hydropathy analysis predicts that all cloned connexins share a common
transmembrane (TM) topology. Each connexin is thought to contain 4 TM
domains, with two extracellular and three cytoplasmic regions. This model
has been validated for several of the family members by in vitro biochemical
analysis. Both N- and C-termini are thought to face the cytoplasm, and the
third TM domain has an amphipathic character, suggesting that it contributes
to the lining of the formed-channel. Amino acid sequence identity between
the isoforms is ~50-80%, with the TM domains being well conserved. Both
extracellular loops contain characteristically conserved cysteine residues,
which likely form intramolecular disulphide bonds. By contrast, the single 
putative intracellular loop (between TM domains 2 and 3) and the cytoplasmic
C-terminus are highly variable among the family members. Six connexins are
thought to associate to form a hemi-channel, or connexon. Two connexons then
interact (likely via the extracellular loops of their connexins) to form the
complete gap junction channel.
 
Two sets of nomenclature have been used to identify the connexins.  The
first, and most commonly used, classifies the connexin molecules according
to molecular weight, such as connexin43 (abbreviated to Cx43), indicating
a connexin of molecular weight close to 43 kDa. However, studies have
revealed cases where clear functional homologues exist across species
that have quite different molecular masses; therefore, an alternative
nomenclature was proposed based on evolutionary considerations, which
divides the family into two major subclasses, alpha and beta, each with a
number of members [5]. Due to their ubiquity and overlapping tissue
distributions, it has proved difficult to elucidate the functions of
individual connexin isoforms. To circumvent this problem, particular
connexin-encoding genes have been subjected to targeted-disruption in mice,
and the phenotype of the resulting animals investigated. Around half the
connexin isoforms have been investigated in this manner [6,7]. Further
insight into the functional roles of connexins has come from the discovery
that a number of human diseases are caused by mutations in connexin genes.
For instance, mutations in Cx32 give rise to a form of inherited
peripheral neuropathy called X-linked dominant Charcot-Marie-Tooth disease
[8]. Similarly, mutations in Cx26 are responsible for both autosomal
recessive and dominant forms of nonsyndromic deafness, a disorder
characterised by hearing loss, with no apparent effects on other organ
systems.
 
Connexin36 (Cx36), which was recently cloned from mammalian brain, encodes
a protein containing 321 amino acid residues and predicted molecular mass
of ~36kDa [9]. The rat and mouse forms of Cx36 are near-identical,
differing by only a single residue. Studies of its distribution (by mRNA
analysis), have found that is is highly expressed in the adult retina of 
these species, and also (less-abundantly) in the brain. Within the latter,
the highest expression levels are found in several discrete regions,
including: the inferior olive, olfactory bulb, the CA3/CA4 sub-fields of 
the hippocampus, and several of the brainstem nuclei.  
 
CONNEXIN36 is a 3-element fingerprint that provides a signature for the
gap junction protein connexin36 (Cx36). The fingerprint was derived from
an initial alignment of 2 sequences: the motifs were drawn from conserved
regions within the central portion of the alignment, focusing on those
sections that characterise the connexin36 isoform but distinguish it from
others - motifs 1-3 reside within the putative cytoplasmic loop located
between TM domains 2 and 3. A single iteration on SPTR37_9f was required to
reach convergence, no further sequences being identified beyond the 
starting set.
Summary Information
2 codes involving  3 elements
0 codes involving 2 elements
Composite Feature Index
3222
2000
123
True Positives
O54851        O70610        
Sequence Titles
O54851      CONNEXIN-36 - MUS MUSCULUS (MOUSE).           
O70610 CONNEXIN36 - RATTUS NORVEGICUS (RAT).
Scan History
SPTR37_9f  1  300  NSINGLE    
Initial Motifs
Motif 1  width=12
Element Seqn Id St Int Rpt
LALDRDPAESIG O54851 114 114 -
LALDRDPAESIG O70610 114 114 -

Motif 2 width=13
Element Seqn Id St Int Rpt
GPGGTGGGGSGGS O54851 126 0 -
GPGGTGGGGSGGS O70610 126 0 -

Motif 3 width=8
Element Seqn Id St Int Rpt
KLQNAMVN O54851 144 5 -
KLQNAIVN O70610 144 5 -
Final Motifs
Motif 1  width=12
Element Seqn Id St Int Rpt
LALDRDPAESIG O54851 114 114 -
LALDRDPAESIG O70610 114 114 -

Motif 2 width=13
Element Seqn Id St Int Rpt
GPGGTGGGGSGGS O54851 126 0 -
GPGGTGGGGSGGS O70610 126 0 -

Motif 3 width=8
Element Seqn Id St Int Rpt
KLQNAMVN O54851 144 5 -
KLQNAIVN O70610 144 5 -